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    25 avril 2011, par

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    13 avril 2011, par

    MediaSPIP uses HTML5 video and audio tags to play multimedia files, taking advantage of the latest W3C innovations supported by modern browsers.
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  • How to get .mp4 videos from motion on a Raspberry Pi ?

    9 octobre 2016, par Maarti

    I use motion on my laptop and it works perfectly in any format. But when I use it on my Raspberry Pi 3 (Raspbian Jessie) with the Raspberry Camera V2, the only formats that work are : .avi and .swf.

    When I choose any other format, the output video is a "0 sec video" that is played and closed instantly.

    I would like to have .mp4 or .ogg output so I can read it easily with HTML5.

    Here is the motion codec documentation.

    Here is my config file :

    ############################################################
    # Daemon
    ############################################################

    # Start in daemon (background) mode and release terminal (default: off)
    daemon on

    # File to store the process ID, also called pid file. (default: not defined)
    process_id_file /var/run/motion/motion.pid

    ############################################################
    # Basic Setup Mode
    ############################################################

    # Start in Setup-Mode, daemon disabled. (default: off)
    setup_mode off


    # Use a file to save logs messages, if not defined stderr and syslog is used. (default: not defined)
    #logfile /mnt/camshare/Cam1/motion.log
    logfile /tmp/motion.log

    # Level of log messages [1..9] (EMR, ALR, CRT, ERR, WRN, NTC, INF, DBG, ALL). (default: 6 / NTC)
    log_level 2

    # Filter to log messages by type (COR, STR, ENC, NET, DBL, EVT, TRK, VID, ALL). (default: ALL)
    log_type all

    ###########################################################
    # Capture device options
    ############################################################

    # Videodevice to be used for capturing  (default /dev/video0)
    # for FreeBSD default is /dev/bktr0
    #videodevice /dev/video0

    # v4l2_palette allows to choose preferable palette to be use by motion
    # to capture from those supported by your videodevice. (default: 17)
    # E.g. if your videodevice supports both V4L2_PIX_FMT_SBGGR8 and
    # V4L2_PIX_FMT_MJPEG then motion will by default use V4L2_PIX_FMT_MJPEG.
    # Setting v4l2_palette to 2 forces motion to use V4L2_PIX_FMT_SBGGR8
    # instead.
    #
    # Values :
    # V4L2_PIX_FMT_SN9C10X : 0  'S910'
    # V4L2_PIX_FMT_SBGGR16 : 1  'BYR2'
    # V4L2_PIX_FMT_SBGGR8  : 2  'BA81'
    # V4L2_PIX_FMT_SPCA561 : 3  'S561'
    # V4L2_PIX_FMT_SGBRG8  : 4  'GBRG'
    # V4L2_PIX_FMT_SGRBG8  : 5  'GRBG'
    # V4L2_PIX_FMT_PAC207  : 6  'P207'
    # V4L2_PIX_FMT_PJPG    : 7  'PJPG'
    # V4L2_PIX_FMT_MJPEG   : 8  'MJPEG'
    # V4L2_PIX_FMT_JPEG    : 9  'JPEG'
    # V4L2_PIX_FMT_RGB24   : 10 'RGB3'
    # V4L2_PIX_FMT_SPCA501 : 11 'S501'
    # V4L2_PIX_FMT_SPCA505 : 12 'S505'
    # V4L2_PIX_FMT_SPCA508 : 13 'S508'
    # V4L2_PIX_FMT_UYVY    : 14 'UYVY'
    # V4L2_PIX_FMT_YUYV    : 15 'YUYV'
    # V4L2_PIX_FMT_YUV422P : 16 '422P'
    # V4L2_PIX_FMT_YUV420  : 17 'YU12'
    #
    v4l2_palette 7

    # Tuner device to be used for capturing using tuner as source (default /dev/tuner0)
    # This is ONLY used for FreeBSD. Leave it commented out for Linux
    ; tunerdevice /dev/tuner0

    # The video input to be used (default: -1)
    # Should normally be set to 0 or 1 for video/TV cards, and -1 for USB cameras
    input -1

    # The video norm to use (only for video capture and TV tuner cards)
    # Values: 0 (PAL), 1 (NTSC), 2 (SECAM), 3 (PAL NC no colour). Default: 0 (PAL)
    norm 0

    # The frequency to set the tuner to (kHz) (only for TV tuner cards) (default: 0)
    frequency 0

    # Rotate image this number of degrees. The rotation affects all saved images as
    # well as movies. Valid values: 0 (default = no rotation), 90, 180 and 270.
    rotate 0

    # Image width (pixels). Valid range: Camera dependent, default: 352
    #width 1024
    width 640

    # Image height (pixels). Valid range: Camera dependent, default: 288
    #height 576
    height 480

    # Maximum number of frames to be captured per second.
    # Valid range: 2-100. Default: 100 (almost no limit).
    framerate 15

    # Minimum time in seconds between capturing picture frames from the camera.
    # Default: 0 = disabled - the capture rate is given by the camera framerate.
    # This option is used when you want to capture images at a rate lower than 2 per second.
    minimum_frame_time 0

    # URL to use if you are using a network camera, size will be autodetected (incl http:// ftp:// mjpg:// or file:///)
    # Must be a URL that returns single jpeg pictures or a raw mjpeg stream. Default: Not defined
    ;netcam_url http://127.0.0.1/cgi-bin/raspicam.sh

    # Username and password for network camera (only if required). Default: not defined
    # Syntax is user:password
    ; netcam_userpass value

    # The setting for keep-alive of network socket, should improve performance on compatible net cameras.
    # off:   The historical implementation using HTTP/1.0, closing the socket after each http request.
    # force: Use HTTP/1.0 requests with keep alive header to reuse the same connection.
    # on:    Use HTTP/1.1 requests that support keep alive as default.
    # Default: off
    netcam_keepalive off

    # URL to use for a netcam proxy server, if required, e.g. "http://myproxy".
    # If a port number other than 80 is needed, use "http://myproxy:1234".
    # Default: not defined
    ; netcam_proxy value

    # Set less strict jpeg checks for network cameras with a poor/buggy firmware.
    # Default: off
    netcam_tolerant_check off

    # Let motion regulate the brightness of a video device (default: off).
    # The auto_brightness feature uses the brightness option as its target value.
    # If brightness is zero auto_brightness will adjust to average brightness value 128.
    # Only recommended for cameras without auto brightness
    auto_brightness off

    # Set the initial brightness of a video device.
    # If auto_brightness is enabled, this value defines the average brightness level
    # which Motion will try and adjust to.
    # Valid range 0-255, default 0 = disabled
    brightness 0

    # Set the contrast of a video device.
    # Valid range 0-255, default 0 = disabled
    contrast 0

    # Set the saturation of a video device.
    # Valid range 0-255, default 0 = disabled
    saturation 0

    # Set the hue of a video device (NTSC feature).
    # Valid range 0-255, default 0 = disabled
    hue 0

    ############################################################
    # File "camera" support - read raw YUV data from a file
    ############################################################
    #filecam_path /home/pi/test-cap/motion-mmal.capture

    ############################################################
    # OpenMax/MMAL camera support for Raspberry Pi
    ############################################################
    mmalcam_name vc.ril.camera
    #mmalcam_control_params
    #mmalcam_raw_capture_file /home/pi/motion-mmal.capture

    # Switch this setting to "on" to use the still image mode of the Pi's camera
    # instead of video. This gives a wider field of view, but requires
    # a much slower frame-rate to achieve exposure stability
    # (e.g. 0.25 fps or slower). You can use the minimum_frame_time
    # parameter above to achieve this

    mmalcam_use_still off


    ############################################################
    # Round Robin (multiple inputs on same video device name)
    ############################################################

    # Number of frames to capture in each roundrobin step (default: 1)
    roundrobin_frames 1

    # Number of frames to skip before each roundrobin step (default: 1)
    roundrobin_skip 1

    # Try to filter out noise generated by roundrobin (default: off)
    switchfilter off


    ############################################################
    # Motion Detection Settings:
    ############################################################

    # Threshold for number of changed pixels in an image that
    # triggers motion detection (default: 1500)
    threshold 1500

    # Automatically tune the threshold down if possible (default: off)
    threshold_tune off

    # Noise threshold for the motion detection (default: 32)
    noise_level 32

    # Automatically tune the noise threshold (default: on)
    noise_tune on

    # Despeckle motion image using (e)rode or (d)ilate or (l)abel (Default: not defined)
    # Recommended value is EedDl. Any combination (and number of) of E, e, d, and D is valid.
    # (l)abeling must only be used once and the 'l' must be the last letter.
    # Comment out to disable
    despeckle_filter EedDl

    # Detect motion in predefined areas (1 - 9). Areas are numbered like that:  1 2 3
    # A script (on_area_detected) is started immediately when motion is         4 5 6
    # detected in one of the given areas, but only once during an event.        7 8 9
    # One or more areas can be specified with this option. Take care: This option
    # does NOT restrict detection to these areas! (Default: not defined)
    ; area_detect value

    # PGM file to use as a sensitivity mask.
    # Full path name to. (Default: not defined)
    ; mask_file value

    # Dynamically create a mask file during operation (default: 0)
    # Adjust speed of mask changes from 0 (off) to 10 (fast)
    smart_mask_speed 0

    # Ignore sudden massive light intensity changes given as a percentage of the picture
    # area that changed intensity. Valid range: 0 - 100 , default: 0 = disabled
    lightswitch 0

    # Picture frames must contain motion at least the specified number of frames
    # in a row before they are detected as true motion. At the default of 1, all
    # motion is detected. Valid range: 1 to thousands, recommended 1-5
    minimum_motion_frames 1

    # Specifies the number of pre-captured (buffered) pictures from before motion
    # was detected that will be output at motion detection.
    # Recommended range: 0 to 5 (default: 0)
    # Do not use large values! Large values will cause Motion to skip video frames and
    # cause unsmooth movies. To smooth movies use larger values of post_capture instead.
    pre_capture 2

    # Number of frames to capture after motion is no longer detected (default: 0)
    post_capture 2

    # Event Gap is the seconds of no motion detection that triggers the end of an event.
    # An event is defined as a series of motion images taken within a short timeframe.
    # Recommended value is 60 seconds (Default). The value -1 is allowed and disables
    # events causing all Motion to be written to one single movie file and no pre_capture.
    # If set to 0, motion is running in gapless mode. Movies don't have gaps anymore. An
    # event ends right after no more motion is detected and post_capture is over.
    event_gap 60

    # Maximum length in seconds of an mpeg movie
    # When value is exceeded a new movie file is created. (Default: 0 = infinite)
    # ATTENTION: when you're not using the motion build from the tutorial, it might fail with error 'Unknown config option "max_mpeg_time"'
    # the use this line instead:
    # max_movie_time 60
    max_movie_time 60

    # Always save images even if there was no motion (default: off)
    emulate_motion off


    ############################################################
    # Image File Output
    ############################################################

    # Output 'normal' pictures when motion is detected (default: on)
    # Valid values: on, off, first, best, center
    # When set to 'first', only the first picture of an event is saved.
    # Picture with most motion of an event is saved when set to 'best'.
    # Picture with motion nearest center of picture is saved when set to 'center'.
    # Can be used as preview shot for the corresponding movie.
    output_pictures best

    # Output pictures with only the pixels moving object (ghost images) (default: off)
    output_debug_pictures off

    # The quality (in percent) to be used by the jpeg compression (default: 75)
    quality 75

    # Type of output images
    # Valid values: jpeg, ppm (default: jpeg)
    picture_type jpeg

    ############################################################
    # FFMPEG related options
    # Film (movies) file output, and deinterlacing of the video input
    # The options movie_filename and timelapse_filename are also used
    # by the ffmpeg feature
    ############################################################

    # Use ffmpeg to encode movies in realtime (default: off)
    ffmpeg_output_movies on

    # Use ffmpeg to make movies with only the pixels moving
    # object (ghost images) (default: off)
    ffmpeg_output_debug_movies off

    # Use ffmpeg to encode a timelapse movie
    # Default value 0 = off - else save frame every Nth second
    ffmpeg_timelapse 0

    # The file rollover mode of the timelapse video
    # Valid values: hourly, daily (default), weekly-sunday, weekly-monday, monthly, manual
    ffmpeg_timelapse_mode daily

    # Bitrate to be used by the ffmpeg encoder (default: 400000)
    # This option is ignored if ffmpeg_variable_bitrate is not 0 (disabled)
    ffmpeg_bps 500000

    # Enables and defines variable bitrate for the ffmpeg encoder.
    # ffmpeg_bps is ignored if variable bitrate is enabled.
    # Valid values: 0 (default) = fixed bitrate defined by ffmpeg_bps,
    # or the range 2 - 31 where 2 means best quality and 31 is worst.
    ffmpeg_variable_bitrate 5

    # Codec to used by ffmpeg for the video compression.
    # Timelapse mpegs are always made in mpeg1 format independent from this option.
    # Supported formats are: mpeg1 (ffmpeg-0.4.8 only), mpeg4 (default), and msmpeg4.
    # mpeg1 - gives you files with extension .mpg
    # mpeg4 or msmpeg4 - gives you files with extension .avi
    # msmpeg4 is recommended for use with Windows Media Player because
    # it requires no installation of codec on the Windows client.
    # swf - gives you a flash film with extension .swf
    # flv - gives you a flash video with extension .flv
    # ffv1 - FF video codec 1 for Lossless Encoding ( experimental )
    # mov - QuickTime ( testing )
    # ogg - Ogg/Theora ( testing )
    #ffmpeg_video_codec msmpeg4
    ffmpeg_video_codec mp4

    # Use ffmpeg to deinterlace video. Necessary if you use an analog camera
    # and see horizontal combing on moving objects in video or pictures.
    # (default: off)
    ffmpeg_deinterlace off

    ############################################################
    # SDL Window
    ############################################################

    # Number of motion thread to show in SDL Window (default: 0 = disabled)
    #sdl_threadnr 0

    ############################################################
    # External pipe to video encoder
    # Replacement for FFMPEG builtin encoder for ffmpeg_output_movies only.
    # The options movie_filename and timelapse_filename are also used
    # by the ffmpeg feature
    #############################################################

    # Bool to enable or disable extpipe (default: off)
    use_extpipe off

    # External program (full path and opts) to pipe raw video to
    # Generally, use '-' for STDIN...
    ;extpipe mencoder -demuxer rawvideo -rawvideo w=320:h=240:i420 -ovc x264 -x264encopts bframes=4:frameref=1:subq=1:scenecut=-1:nob_adapt:threads=1:keyint=1000:8x8dct:vbv_bufsize=4000:crf=24:partitions=i8x8,i4x4:vbv_maxrate=800:no-chroma-me -vf denoise3d=16:12:48:4,pp=lb -of   avi -o %f.avi - -fps %fps



    ############################################################
    # Snapshots (Traditional Periodic Webcam File Output)
    ############################################################

    # Make automated snapshot every N seconds (default: 0 = disabled)
    snapshot_interval 0


    ############################################################
    # Text Display
    # %Y = year, %m = month, %d = date,
    # %H = hour, %M = minute, %S = second, %T = HH:MM:SS,
    # %v = event, %q = frame number, %t = thread (camera) number,
    # %D = changed pixels, %N = noise level, \n = new line,
    # %i and %J = width and height of motion area,
    # %K and %L = X and Y coordinates of motion center
    # %C = value defined by text_event - do not use with text_event!
    # You can put quotation marks around the text to allow
    # leading spaces
    ############################################################

    # Locate and draw a box around the moving object.
    # Valid values: on, off, preview (default: off)
    # Set to 'preview' will only draw a box in preview_shot pictures.
    locate_motion_mode off

    # Set the look and style of the locate box if enabled.
    # Valid values: box, redbox, cross, redcross (default: box)
    # Set to 'box' will draw the traditional box.
    # Set to 'redbox' will draw a red box.
    # Set to 'cross' will draw a little cross to mark center.
    # Set to 'redcross' will draw a little red cross to mark center.
    locate_motion_style box

    # Draws the timestamp using same options as C function strftime(3)
    # Default: %Y-%m-%d\n%T = date in ISO format and time in 24 hour clock
    # Text is placed in lower right corner
    text_right %d.%m.%Y\n%T

    # Draw a user defined text on the images using same options as C function strftime(3)
    # Default: Not defined = no text
    # Text is placed in lower left corner
    ; text_left CAMERA %t
    text_left HofCam

    # Draw the number of changed pixed on the images (default: off)
    # Will normally be set to off except when you setup and adjust the motion settings
    # Text is placed in upper right corner
    text_changes off

    # This option defines the value of the special event conversion specifier %C
    # You can use any conversion specifier in this option except %C. Date and time
    # values are from the timestamp of the first image in the current event.
    # Default: %Y%m%d%H%M%S
    # The idea is that %C can be used filenames and text_left/right for creating
    # a unique identifier for each event.
    text_event %Y%m%d%H%M%S

    # Draw characters at twice normal size on images. (default: off)
    text_double on


    # Text to include in a JPEG EXIF comment
    # May be any text, including conversion specifiers.
    # The EXIF timestamp is included independent of this text.
    ;exif_text %i%J/%K%L

    ############################################################
    # Target Directories and filenames For Images And Films
    # For the options snapshot_, picture_, movie_ and timelapse_filename
    # you can use conversion specifiers
    # %Y = year, %m = month, %d = date,
    # %H = hour, %M = minute, %S = second,
    # %v = event, %q = frame number, %t = thread (camera) number,
    # %D = changed pixels, %N = noise level,
    # %i and %J = width and height of motion area,
    # %K and %L = X and Y coordinates of motion center
    # %C = value defined by text_event
    # Quotation marks round string are allowed.
    ############################################################

    # Target base directory for pictures and films
    # Recommended to use absolute path. (Default: current working directory)
    target_dir /home/pi

    # File path for snapshots (jpeg or ppm) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S-snapshot
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H/%M/%S-snapshot
    # File extension .jpg or .ppm is automatically added so do not include this.
    # Note: A symbolic link called lastsnap.jpg created in the target_dir will always
    # point to the latest snapshot, unless snapshot_filename is exactly 'lastsnap'
    snapshot_filename %v-%Y%m%d%H%M%S-snapshot

    # File path for motion triggered images (jpeg or ppm) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S-%q
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H/%M/%S-%q
    # File extension .jpg or .ppm is automatically added so do not include this
    # Set to 'preview' together with best-preview feature enables special naming
    # convention for preview shots. See motion guide for details
    picture_filename %v-%Y%m%d%H%M%S-%q

    # File path for motion triggered ffmpeg films (movies) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H%M%S
    # File extension .mpg or .avi is automatically added so do not include this
    # This option was previously called ffmpeg_filename
    movie_filename %v-%Y%m%d%H%M%S

    # File path for timelapse movies relative to target_dir
    # Default: %Y%m%d-timelapse
    # Default value is near equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d-timelapse
    # File extension .mpg is automatically added so do not include this
    timelapse_filename %Y%m%d-timelapse

    ############################################################
    # Global Network Options
    ############################################################
    # Enable or disable IPV6 for http control and stream (default: off )
    ipv6_enabled off

    ############################################################
    # Live Stream Server
    ############################################################

    # The mini-http server listens to this port for requests (default: 0 = disabled)
    stream_port 8080

    # Quality of the jpeg (in percent) images produced (default: 50)
    stream_quality 50

    # Output frames at 1 fps when no motion is detected and increase to the
    # rate given by stream_maxrate when motion is detected (default: off)
    stream_motion on

    # Maximum framerate for stream streams (default: 1)
    stream_maxrate 4

    # Restrict stream connections to localhost only (default: on)
    stream_localhost off

    # Limits the number of images per connection (default: 0 = unlimited)
    # Number can be defined by multiplying actual stream rate by desired number of seconds
    # Actual stream rate is the smallest of the numbers framerate and stream_maxrate
    stream_limit 0

    # Set the authentication method (default: 0)
    # 0 = disabled
    # 1 = Basic authentication
    # 2 = MD5 digest (the safer authentication)
    stream_auth_method 0

    # Authentication for the stream. Syntax username:password
    # Default: not defined (Disabled)
    ; stream_authentication username:password


    ############################################################
    # HTTP Based Control
    ############################################################

    # TCP/IP port for the http server to listen on (default: 0 = disabled)
    webcontrol_port 8081

    # Restrict control connections to localhost only (default: on)
    webcontrol_localhost off

    # Output for http server, select off to choose raw text plain (default: on)
    webcontrol_html_output on

    # Authentication for the http based control. Syntax username:password
    # Default: not defined (Disabled)
    ; webcontrol_authentication username:password


    ############################################################
    # Tracking (Pan/Tilt)
    #############################################################

    # Type of tracker (0=none (default), 1=stepper, 2=iomojo, 3=pwc, 4=generic, 5=uvcvideo, 6=servo)
    # The generic type enables the definition of motion center and motion size to
    # be used with the conversion specifiers for options like on_motion_detected
    track_type 0

    # Enable auto tracking (default: off)
    track_auto off

    # Serial port of motor (default: none)
    ;track_port /dev/ttyS0

    # Motor number for x-axis (default: 0)
    ;track_motorx 0

    # Set motorx reverse (default: 0)
    ;track_motorx_reverse 0

    # Motor number for y-axis (default: 0)
    ;track_motory 1

    # Set motory reverse (default: 0)
    ;track_motory_reverse 0

    # Maximum value on x-axis (default: 0)
    ;track_maxx 200

    # Minimum value on x-axis (default: 0)
    ;track_minx 50

    # Maximum value on y-axis (default: 0)
    ;track_maxy 200

    # Minimum value on y-axis (default: 0)
    ;track_miny 50

    # Center value on x-axis (default: 0)
    ;track_homex 128

    # Center value on y-axis (default: 0)
    ;track_homey 128

    # ID of an iomojo camera if used (default: 0)
    track_iomojo_id 0

    # Angle in degrees the camera moves per step on the X-axis
    # with auto-track (default: 10)
    # Currently only used with pwc type cameras
    track_step_angle_x 10

    [...]
  • How to get .mp4 videos from motion on a Raspberry Pi ?

    3 novembre 2017, par Maarti

    I use motion on my laptop and it works perfectly in any format. But when I use it on my Raspberry Pi 3 (Raspbian Jessie) with the Raspberry Camera V2, the only formats that work are : .avi and .swf.

    When I choose any other format, the output video is a "0 sec video" that is played and closed instantly.

    I would like to have .mp4 or .ogg output so I can read it easily with HTML5.

    Here is the motion codec documentation.

    Here is my config file :

    ############################################################
    # Daemon
    ############################################################

    # Start in daemon (background) mode and release terminal (default: off)
    daemon on

    # File to store the process ID, also called pid file. (default: not defined)
    process_id_file /var/run/motion/motion.pid

    ############################################################
    # Basic Setup Mode
    ############################################################

    # Start in Setup-Mode, daemon disabled. (default: off)
    setup_mode off


    # Use a file to save logs messages, if not defined stderr and syslog is used. (default: not defined)
    #logfile /mnt/camshare/Cam1/motion.log
    logfile /tmp/motion.log

    # Level of log messages [1..9] (EMR, ALR, CRT, ERR, WRN, NTC, INF, DBG, ALL). (default: 6 / NTC)
    log_level 2

    # Filter to log messages by type (COR, STR, ENC, NET, DBL, EVT, TRK, VID, ALL). (default: ALL)
    log_type all

    ###########################################################
    # Capture device options
    ############################################################

    # Videodevice to be used for capturing  (default /dev/video0)
    # for FreeBSD default is /dev/bktr0
    #videodevice /dev/video0

    # v4l2_palette allows to choose preferable palette to be use by motion
    # to capture from those supported by your videodevice. (default: 17)
    # E.g. if your videodevice supports both V4L2_PIX_FMT_SBGGR8 and
    # V4L2_PIX_FMT_MJPEG then motion will by default use V4L2_PIX_FMT_MJPEG.
    # Setting v4l2_palette to 2 forces motion to use V4L2_PIX_FMT_SBGGR8
    # instead.
    #
    # Values :
    # V4L2_PIX_FMT_SN9C10X : 0  'S910'
    # V4L2_PIX_FMT_SBGGR16 : 1  'BYR2'
    # V4L2_PIX_FMT_SBGGR8  : 2  'BA81'
    # V4L2_PIX_FMT_SPCA561 : 3  'S561'
    # V4L2_PIX_FMT_SGBRG8  : 4  'GBRG'
    # V4L2_PIX_FMT_SGRBG8  : 5  'GRBG'
    # V4L2_PIX_FMT_PAC207  : 6  'P207'
    # V4L2_PIX_FMT_PJPG    : 7  'PJPG'
    # V4L2_PIX_FMT_MJPEG   : 8  'MJPEG'
    # V4L2_PIX_FMT_JPEG    : 9  'JPEG'
    # V4L2_PIX_FMT_RGB24   : 10 'RGB3'
    # V4L2_PIX_FMT_SPCA501 : 11 'S501'
    # V4L2_PIX_FMT_SPCA505 : 12 'S505'
    # V4L2_PIX_FMT_SPCA508 : 13 'S508'
    # V4L2_PIX_FMT_UYVY    : 14 'UYVY'
    # V4L2_PIX_FMT_YUYV    : 15 'YUYV'
    # V4L2_PIX_FMT_YUV422P : 16 '422P'
    # V4L2_PIX_FMT_YUV420  : 17 'YU12'
    #
    v4l2_palette 7

    # Tuner device to be used for capturing using tuner as source (default /dev/tuner0)
    # This is ONLY used for FreeBSD. Leave it commented out for Linux
    ; tunerdevice /dev/tuner0

    # The video input to be used (default: -1)
    # Should normally be set to 0 or 1 for video/TV cards, and -1 for USB cameras
    input -1

    # The video norm to use (only for video capture and TV tuner cards)
    # Values: 0 (PAL), 1 (NTSC), 2 (SECAM), 3 (PAL NC no colour). Default: 0 (PAL)
    norm 0

    # The frequency to set the tuner to (kHz) (only for TV tuner cards) (default: 0)
    frequency 0

    # Rotate image this number of degrees. The rotation affects all saved images as
    # well as movies. Valid values: 0 (default = no rotation), 90, 180 and 270.
    rotate 0

    # Image width (pixels). Valid range: Camera dependent, default: 352
    #width 1024
    width 640

    # Image height (pixels). Valid range: Camera dependent, default: 288
    #height 576
    height 480

    # Maximum number of frames to be captured per second.
    # Valid range: 2-100. Default: 100 (almost no limit).
    framerate 15

    # Minimum time in seconds between capturing picture frames from the camera.
    # Default: 0 = disabled - the capture rate is given by the camera framerate.
    # This option is used when you want to capture images at a rate lower than 2 per second.
    minimum_frame_time 0

    # URL to use if you are using a network camera, size will be autodetected (incl http:// ftp:// mjpg:// or file:///)
    # Must be a URL that returns single jpeg pictures or a raw mjpeg stream. Default: Not defined
    ;netcam_url http://127.0.0.1/cgi-bin/raspicam.sh

    # Username and password for network camera (only if required). Default: not defined
    # Syntax is user:password
    ; netcam_userpass value

    # The setting for keep-alive of network socket, should improve performance on compatible net cameras.
    # off:   The historical implementation using HTTP/1.0, closing the socket after each http request.
    # force: Use HTTP/1.0 requests with keep alive header to reuse the same connection.
    # on:    Use HTTP/1.1 requests that support keep alive as default.
    # Default: off
    netcam_keepalive off

    # URL to use for a netcam proxy server, if required, e.g. "http://myproxy".
    # If a port number other than 80 is needed, use "http://myproxy:1234".
    # Default: not defined
    ; netcam_proxy value

    # Set less strict jpeg checks for network cameras with a poor/buggy firmware.
    # Default: off
    netcam_tolerant_check off

    # Let motion regulate the brightness of a video device (default: off).
    # The auto_brightness feature uses the brightness option as its target value.
    # If brightness is zero auto_brightness will adjust to average brightness value 128.
    # Only recommended for cameras without auto brightness
    auto_brightness off

    # Set the initial brightness of a video device.
    # If auto_brightness is enabled, this value defines the average brightness level
    # which Motion will try and adjust to.
    # Valid range 0-255, default 0 = disabled
    brightness 0

    # Set the contrast of a video device.
    # Valid range 0-255, default 0 = disabled
    contrast 0

    # Set the saturation of a video device.
    # Valid range 0-255, default 0 = disabled
    saturation 0

    # Set the hue of a video device (NTSC feature).
    # Valid range 0-255, default 0 = disabled
    hue 0

    ############################################################
    # File "camera" support - read raw YUV data from a file
    ############################################################
    #filecam_path /home/pi/test-cap/motion-mmal.capture

    ############################################################
    # OpenMax/MMAL camera support for Raspberry Pi
    ############################################################
    mmalcam_name vc.ril.camera
    #mmalcam_control_params
    #mmalcam_raw_capture_file /home/pi/motion-mmal.capture

    # Switch this setting to "on" to use the still image mode of the Pi's camera
    # instead of video. This gives a wider field of view, but requires
    # a much slower frame-rate to achieve exposure stability
    # (e.g. 0.25 fps or slower). You can use the minimum_frame_time
    # parameter above to achieve this

    mmalcam_use_still off


    ############################################################
    # Round Robin (multiple inputs on same video device name)
    ############################################################

    # Number of frames to capture in each roundrobin step (default: 1)
    roundrobin_frames 1

    # Number of frames to skip before each roundrobin step (default: 1)
    roundrobin_skip 1

    # Try to filter out noise generated by roundrobin (default: off)
    switchfilter off


    ############################################################
    # Motion Detection Settings:
    ############################################################

    # Threshold for number of changed pixels in an image that
    # triggers motion detection (default: 1500)
    threshold 1500

    # Automatically tune the threshold down if possible (default: off)
    threshold_tune off

    # Noise threshold for the motion detection (default: 32)
    noise_level 32

    # Automatically tune the noise threshold (default: on)
    noise_tune on

    # Despeckle motion image using (e)rode or (d)ilate or (l)abel (Default: not defined)
    # Recommended value is EedDl. Any combination (and number of) of E, e, d, and D is valid.
    # (l)abeling must only be used once and the 'l' must be the last letter.
    # Comment out to disable
    despeckle_filter EedDl

    # Detect motion in predefined areas (1 - 9). Areas are numbered like that:  1 2 3
    # A script (on_area_detected) is started immediately when motion is         4 5 6
    # detected in one of the given areas, but only once during an event.        7 8 9
    # One or more areas can be specified with this option. Take care: This option
    # does NOT restrict detection to these areas! (Default: not defined)
    ; area_detect value

    # PGM file to use as a sensitivity mask.
    # Full path name to. (Default: not defined)
    ; mask_file value

    # Dynamically create a mask file during operation (default: 0)
    # Adjust speed of mask changes from 0 (off) to 10 (fast)
    smart_mask_speed 0

    # Ignore sudden massive light intensity changes given as a percentage of the picture
    # area that changed intensity. Valid range: 0 - 100 , default: 0 = disabled
    lightswitch 0

    # Picture frames must contain motion at least the specified number of frames
    # in a row before they are detected as true motion. At the default of 1, all
    # motion is detected. Valid range: 1 to thousands, recommended 1-5
    minimum_motion_frames 1

    # Specifies the number of pre-captured (buffered) pictures from before motion
    # was detected that will be output at motion detection.
    # Recommended range: 0 to 5 (default: 0)
    # Do not use large values! Large values will cause Motion to skip video frames and
    # cause unsmooth movies. To smooth movies use larger values of post_capture instead.
    pre_capture 2

    # Number of frames to capture after motion is no longer detected (default: 0)
    post_capture 2

    # Event Gap is the seconds of no motion detection that triggers the end of an event.
    # An event is defined as a series of motion images taken within a short timeframe.
    # Recommended value is 60 seconds (Default). The value -1 is allowed and disables
    # events causing all Motion to be written to one single movie file and no pre_capture.
    # If set to 0, motion is running in gapless mode. Movies don't have gaps anymore. An
    # event ends right after no more motion is detected and post_capture is over.
    event_gap 60

    # Maximum length in seconds of an mpeg movie
    # When value is exceeded a new movie file is created. (Default: 0 = infinite)
    # ATTENTION: when you're not using the motion build from the tutorial, it might fail with error 'Unknown config option "max_mpeg_time"'
    # the use this line instead:
    # max_movie_time 60
    max_movie_time 60

    # Always save images even if there was no motion (default: off)
    emulate_motion off


    ############################################################
    # Image File Output
    ############################################################

    # Output 'normal' pictures when motion is detected (default: on)
    # Valid values: on, off, first, best, center
    # When set to 'first', only the first picture of an event is saved.
    # Picture with most motion of an event is saved when set to 'best'.
    # Picture with motion nearest center of picture is saved when set to 'center'.
    # Can be used as preview shot for the corresponding movie.
    output_pictures best

    # Output pictures with only the pixels moving object (ghost images) (default: off)
    output_debug_pictures off

    # The quality (in percent) to be used by the jpeg compression (default: 75)
    quality 75

    # Type of output images
    # Valid values: jpeg, ppm (default: jpeg)
    picture_type jpeg

    ############################################################
    # FFMPEG related options
    # Film (movies) file output, and deinterlacing of the video input
    # The options movie_filename and timelapse_filename are also used
    # by the ffmpeg feature
    ############################################################

    # Use ffmpeg to encode movies in realtime (default: off)
    ffmpeg_output_movies on

    # Use ffmpeg to make movies with only the pixels moving
    # object (ghost images) (default: off)
    ffmpeg_output_debug_movies off

    # Use ffmpeg to encode a timelapse movie
    # Default value 0 = off - else save frame every Nth second
    ffmpeg_timelapse 0

    # The file rollover mode of the timelapse video
    # Valid values: hourly, daily (default), weekly-sunday, weekly-monday, monthly, manual
    ffmpeg_timelapse_mode daily

    # Bitrate to be used by the ffmpeg encoder (default: 400000)
    # This option is ignored if ffmpeg_variable_bitrate is not 0 (disabled)
    ffmpeg_bps 500000

    # Enables and defines variable bitrate for the ffmpeg encoder.
    # ffmpeg_bps is ignored if variable bitrate is enabled.
    # Valid values: 0 (default) = fixed bitrate defined by ffmpeg_bps,
    # or the range 2 - 31 where 2 means best quality and 31 is worst.
    ffmpeg_variable_bitrate 5

    # Codec to used by ffmpeg for the video compression.
    # Timelapse mpegs are always made in mpeg1 format independent from this option.
    # Supported formats are: mpeg1 (ffmpeg-0.4.8 only), mpeg4 (default), and msmpeg4.
    # mpeg1 - gives you files with extension .mpg
    # mpeg4 or msmpeg4 - gives you files with extension .avi
    # msmpeg4 is recommended for use with Windows Media Player because
    # it requires no installation of codec on the Windows client.
    # swf - gives you a flash film with extension .swf
    # flv - gives you a flash video with extension .flv
    # ffv1 - FF video codec 1 for Lossless Encoding ( experimental )
    # mov - QuickTime ( testing )
    # ogg - Ogg/Theora ( testing )
    #ffmpeg_video_codec msmpeg4
    ffmpeg_video_codec mp4

    # Use ffmpeg to deinterlace video. Necessary if you use an analog camera
    # and see horizontal combing on moving objects in video or pictures.
    # (default: off)
    ffmpeg_deinterlace off

    ############################################################
    # SDL Window
    ############################################################

    # Number of motion thread to show in SDL Window (default: 0 = disabled)
    #sdl_threadnr 0

    ############################################################
    # External pipe to video encoder
    # Replacement for FFMPEG builtin encoder for ffmpeg_output_movies only.
    # The options movie_filename and timelapse_filename are also used
    # by the ffmpeg feature
    #############################################################

    # Bool to enable or disable extpipe (default: off)
    use_extpipe off

    # External program (full path and opts) to pipe raw video to
    # Generally, use '-' for STDIN...
    ;extpipe mencoder -demuxer rawvideo -rawvideo w=320:h=240:i420 -ovc x264 -x264encopts bframes=4:frameref=1:subq=1:scenecut=-1:nob_adapt:threads=1:keyint=1000:8x8dct:vbv_bufsize=4000:crf=24:partitions=i8x8,i4x4:vbv_maxrate=800:no-chroma-me -vf denoise3d=16:12:48:4,pp=lb -of   avi -o %f.avi - -fps %fps



    ############################################################
    # Snapshots (Traditional Periodic Webcam File Output)
    ############################################################

    # Make automated snapshot every N seconds (default: 0 = disabled)
    snapshot_interval 0


    ############################################################
    # Text Display
    # %Y = year, %m = month, %d = date,
    # %H = hour, %M = minute, %S = second, %T = HH:MM:SS,
    # %v = event, %q = frame number, %t = thread (camera) number,
    # %D = changed pixels, %N = noise level, \n = new line,
    # %i and %J = width and height of motion area,
    # %K and %L = X and Y coordinates of motion center
    # %C = value defined by text_event - do not use with text_event!
    # You can put quotation marks around the text to allow
    # leading spaces
    ############################################################

    # Locate and draw a box around the moving object.
    # Valid values: on, off, preview (default: off)
    # Set to 'preview' will only draw a box in preview_shot pictures.
    locate_motion_mode off

    # Set the look and style of the locate box if enabled.
    # Valid values: box, redbox, cross, redcross (default: box)
    # Set to 'box' will draw the traditional box.
    # Set to 'redbox' will draw a red box.
    # Set to 'cross' will draw a little cross to mark center.
    # Set to 'redcross' will draw a little red cross to mark center.
    locate_motion_style box

    # Draws the timestamp using same options as C function strftime(3)
    # Default: %Y-%m-%d\n%T = date in ISO format and time in 24 hour clock
    # Text is placed in lower right corner
    text_right %d.%m.%Y\n%T

    # Draw a user defined text on the images using same options as C function strftime(3)
    # Default: Not defined = no text
    # Text is placed in lower left corner
    ; text_left CAMERA %t
    text_left HofCam

    # Draw the number of changed pixed on the images (default: off)
    # Will normally be set to off except when you setup and adjust the motion settings
    # Text is placed in upper right corner
    text_changes off

    # This option defines the value of the special event conversion specifier %C
    # You can use any conversion specifier in this option except %C. Date and time
    # values are from the timestamp of the first image in the current event.
    # Default: %Y%m%d%H%M%S
    # The idea is that %C can be used filenames and text_left/right for creating
    # a unique identifier for each event.
    text_event %Y%m%d%H%M%S

    # Draw characters at twice normal size on images. (default: off)
    text_double on


    # Text to include in a JPEG EXIF comment
    # May be any text, including conversion specifiers.
    # The EXIF timestamp is included independent of this text.
    ;exif_text %i%J/%K%L

    ############################################################
    # Target Directories and filenames For Images And Films
    # For the options snapshot_, picture_, movie_ and timelapse_filename
    # you can use conversion specifiers
    # %Y = year, %m = month, %d = date,
    # %H = hour, %M = minute, %S = second,
    # %v = event, %q = frame number, %t = thread (camera) number,
    # %D = changed pixels, %N = noise level,
    # %i and %J = width and height of motion area,
    # %K and %L = X and Y coordinates of motion center
    # %C = value defined by text_event
    # Quotation marks round string are allowed.
    ############################################################

    # Target base directory for pictures and films
    # Recommended to use absolute path. (Default: current working directory)
    target_dir /home/pi

    # File path for snapshots (jpeg or ppm) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S-snapshot
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H/%M/%S-snapshot
    # File extension .jpg or .ppm is automatically added so do not include this.
    # Note: A symbolic link called lastsnap.jpg created in the target_dir will always
    # point to the latest snapshot, unless snapshot_filename is exactly 'lastsnap'
    snapshot_filename %v-%Y%m%d%H%M%S-snapshot

    # File path for motion triggered images (jpeg or ppm) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S-%q
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H/%M/%S-%q
    # File extension .jpg or .ppm is automatically added so do not include this
    # Set to 'preview' together with best-preview feature enables special naming
    # convention for preview shots. See motion guide for details
    picture_filename %v-%Y%m%d%H%M%S-%q

    # File path for motion triggered ffmpeg films (movies) relative to target_dir
    # Default: %v-%Y%m%d%H%M%S
    # Default value is equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d/%H%M%S
    # File extension .mpg or .avi is automatically added so do not include this
    # This option was previously called ffmpeg_filename
    movie_filename %v-%Y%m%d%H%M%S

    # File path for timelapse movies relative to target_dir
    # Default: %Y%m%d-timelapse
    # Default value is near equivalent to legacy oldlayout option
    # For Motion 3.0 compatible mode choose: %Y/%m/%d-timelapse
    # File extension .mpg is automatically added so do not include this
    timelapse_filename %Y%m%d-timelapse

    ############################################################
    # Global Network Options
    ############################################################
    # Enable or disable IPV6 for http control and stream (default: off )
    ipv6_enabled off

    ############################################################
    # Live Stream Server
    ############################################################

    # The mini-http server listens to this port for requests (default: 0 = disabled)
    stream_port 8080

    # Quality of the jpeg (in percent) images produced (default: 50)
    stream_quality 50

    # Output frames at 1 fps when no motion is detected and increase to the
    # rate given by stream_maxrate when motion is detected (default: off)
    stream_motion on

    # Maximum framerate for stream streams (default: 1)
    stream_maxrate 4

    # Restrict stream connections to localhost only (default: on)
    stream_localhost off

    # Limits the number of images per connection (default: 0 = unlimited)
    # Number can be defined by multiplying actual stream rate by desired number of seconds
    # Actual stream rate is the smallest of the numbers framerate and stream_maxrate
    stream_limit 0

    # Set the authentication method (default: 0)
    # 0 = disabled
    # 1 = Basic authentication
    # 2 = MD5 digest (the safer authentication)
    stream_auth_method 0

    # Authentication for the stream. Syntax username:password
    # Default: not defined (Disabled)
    ; stream_authentication username:password


    ############################################################
    # HTTP Based Control
    ############################################################

    # TCP/IP port for the http server to listen on (default: 0 = disabled)
    webcontrol_port 8081

    # Restrict control connections to localhost only (default: on)
    webcontrol_localhost off

    # Output for http server, select off to choose raw text plain (default: on)
    webcontrol_html_output on

    # Authentication for the http based control. Syntax username:password
    # Default: not defined (Disabled)
    ; webcontrol_authentication username:password


    ############################################################
    # Tracking (Pan/Tilt)
    #############################################################

    # Type of tracker (0=none (default), 1=stepper, 2=iomojo, 3=pwc, 4=generic, 5=uvcvideo, 6=servo)
    # The generic type enables the definition of motion center and motion size to
    # be used with the conversion specifiers for options like on_motion_detected
    track_type 0

    # Enable auto tracking (default: off)
    track_auto off

    # Serial port of motor (default: none)
    ;track_port /dev/ttyS0

    # Motor number for x-axis (default: 0)
    ;track_motorx 0

    # Set motorx reverse (default: 0)
    ;track_motorx_reverse 0

    # Motor number for y-axis (default: 0)
    ;track_motory 1

    # Set motory reverse (default: 0)
    ;track_motory_reverse 0

    # Maximum value on x-axis (default: 0)
    ;track_maxx 200

    # Minimum value on x-axis (default: 0)
    ;track_minx 50

    # Maximum value on y-axis (default: 0)
    ;track_maxy 200

    # Minimum value on y-axis (default: 0)
    ;track_miny 50

    # Center value on x-axis (default: 0)
    ;track_homex 128

    # Center value on y-axis (default: 0)
    ;track_homey 128

    # ID of an iomojo camera if used (default: 0)
    track_iomojo_id 0

    # Angle in degrees the camera moves per step on the X-axis
    # with auto-track (default: 10)
    # Currently only used with pwc type cameras
    track_step_angle_x 10

    [...]
  • A systematic approach to making Web Applications accessible

    22 février 2012, par silvia

    With the latest developments in HTML5 and the still fairly new ARIA (Accessible Rich Interface Applications) attributes introduced by the W3C WAI (Web Accessibility Initiative), browsers have now implemented many features that allow you to make your JavaScript-heavy Web applications accessible.

    Since I began working on making a complex web application accessible just over a year ago, I discovered that there was no step-by-step guide to approaching the changes necessary for creating an accessible Web application. Therefore, many people believe that it is still hard, if not impossible, to make Web applications accessible. In fact, it can be approached systematically, as this article will describe.

    This post is based on a talk that Alice Boxhall and I gave at the recent Linux.conf.au titled “Developing accessible Web apps – how hard can it be ?” (slides, video), which in turn was based on a Google Developer Day talk by Rachel Shearer (slides).

    These talks, and this article, introduce a process that you can follow to make your Web applications accessible : each step will take you closer to having an application that can be accessed using a keyboard alone, and by users of screenreaders and other accessibility technology (AT).

    The recommendations here only roughly conform to the requirements of WCAG (Web Content Accessibility Guidelines), which is the basis of legal accessibility requirements in many jurisdictions. The steps in this article may or may not be sufficient to meet a legal requirement. It is focused on the practical outcome of ensuring users with disabilities can use your Web application.

    Step-by-step Approach

    The steps to follow to make your Web apps accessible are as follows :

    1. Use native HTML tags wherever possible
    2. Make interactive elements keyboard accessible
    3. Provide extra markup for AT (accessibility technology)

    If you are a total newcomer to accessibility, I highly recommend installing a screenreader and just trying to read/navigate some Web pages. On Windows you can install the free NVDA screenreader, on Mac you can activate the pre-installed VoiceOver screenreader, on Linux you can use Orca, and if you just want a browser plugin for Chrome try installing ChromeVox.

    1. Use native HTML tags

    As you implement your Web application with interactive controls, try to use as many native HTML tags as possible.

    HTML5 provides a rich set of elements which can be used to both add functionality and provide semantic context to your page. HTML4 already included many useful interactive controls, like <a>, <button>, <input> and <select>, and semantic landmark elements like <h1>. HTML5 adds richer <input> controls, and a more sophisticated set of semantic markup elements like such as <time>, <progress>, <meter>, <nav>, <header>, <article> and <aside>. (Note : check browser support for browser support of the new tags).

    Using as much of the rich HTML5 markup as possible means that you get all of the accessibility features which have been implemented in the browser for those elements, such as keyboard support, short-cut keys and accessibility metadata, for free. For generic tags you have to implement them completely from scratch.

    What exactly do you miss out on when you use a generic tag such as <div> over a specific semantic one such as <button> ?

    1. Generic tags are not focusable. That means you cannot reach them through using the [tab] on the keyboard.
    2. You cannot activate them with the space bar or enter key or perform any other keyboard interaction that would be regarded as typical with such a control.
    3. Since the role that the control represents is not specified in code but is only exposed through your custom visual styling, screenreaders cannot express to their users what type of control it is, e.g. button or link.
    4. Neither can screenreaders add the control to the list of controls on the page that are of a certain type, e.g. to navigate to all headers of a certain level on the page.
    5. And finally you need to manually style the element in order for it to look distinctive compared to other elements on the page ; using a default control will allow the browser to provide the default style for the platform, which you can still override using CSS if you want.

    Example :

    Compare these two buttons. The first one is implemented using a <div> tag, the second one using a <button> tag. Try using a screenreader to experience the difference.

    Send
    <style>
     .custombutton 
      cursor : pointer ;
      border : 1px solid #000 ;
      background-color : #F6F6F6 ;
      display : inline-block ;
      padding : 2px 5px ;
    
    </style>
    <div class="custombutton" onclick="alert(’sent !’)">
      Send
    </div>
    
    <button onclick="alert(’sent !’)">
    Send
    </button>

    2. Make interactive elements keyboard accessible

    Many sophisticated web applications have some interactive controls that just have no appropriate HTML tag equivalent. In this case, you will have had to build an interactive element with JavaScript and <div> and/or <span> tags and lots of custom styling. The good news is, it’s possible to make even these custom controls accessible, and as a side benefit you will also make your application smoother to use for power users.

    The first thing you can do to test usability of your control, or your Web app, is to unplug the mouse and try to use only the [TAB] and [ENTER] keys to interact with your application.

    the tab key on the keyboardthe enter key on the keyboard

    Try the following :

    • Can you reach all interactive elements with [TAB] ?
    • Can you activate interactive elements with [ENTER] (or [SPACE]) ?
    • Are the elements in the right tab order ?
    • After interaction : is the right element in focus ?
    • Is there a keyboard shortcut that activates the element (accesskey) ?

    No ? Let’s fix it.

    2.1. Reaching interactive elements

    If you have an element on your page that cannot be reached with [TAB], put a @tabindex attribute on it.

    Example :

    Here we have a <span> tag that works as a link (don’t do this – it’s just a simple example). The first one cannot be reached using [TAB] but the second one has a tabindex and is thus part of the tab order of the HTML page.

    (Note : since we experiment lots with the tabindex in this article, to avoid confusion, click on some text in this paragraph and then hit the [TAB] key to see where it goes next. The click will set your keyboard focus in the DOM.)

    Click

    <style>
    .customlink 
      text-decoration : underline ;
      cursor : pointer ;
    
    </style>
    <span class="customlink" onclick="alert(’activated !’)">
    Click
    </span>
    
    Click
    <style>
    .customlink 
      text-decoration : underline ;
      cursor : pointer ;
    
    </style>
    <span class="customlink" onclick="alert(’activated !’)" tabindex="0">
    Click
    </span>
    

    You set @tabindex=0 to add an element into the native tab order of the page, which is the DOM order.

    2.2. Activating interactive elements

    Next, you typically want to be able to use the [ENTER] and [SPACE] keys to activate your custom control. To do so, you will need to implement an onkeydown event handler. Note that the keyCode for [ENTER] is 13 and for [SPACE] is 32.

    Example :

    Let’s add this functionality to the <span> tag from before. Try tabbing to it and hit the [ENTER] or [SPACE] key.

    Click
    <span class="customlink" onclick="alert(’activated !’)" tabindex="0">
    Click
    </span>
    
    &lt;script&gt;<br />
    function handlekey(event) {<br />
    var target = event.target || event.srcElement;<br />
    if (event.keyCode == 13 || event.keyCode == 32) { target.onclick(); }<br />
    }<br />
    &lt;/script&gt;


    Click

    <span class="customlink" onclick="alert(’activated !’)" tabindex="0"
          onkeydown="handlekey(event) ;">
    Click
    </span>
    <script>
    function handlekey(event) 
      var target = event.target || event.srcElement ;
      if (event.keyCode == 13 || event.keyCode == 32) 
        target.onclick() ;
      
    
    </script>

    Note that there are some controls that might need support for keys other than [tab] or [enter] to be able to use them from the keyboard alone, for example a custom list box, menu or slider should respond to arrow keys.

    2.3. Elements in the right tab order

    Have you tried tabbing to all the elements on your page that you care about ? If so, check if the order of tab stops seems right. The default order is given by the order in which interactive elements appear in the DOM. For example, if your page’s code has a right column that is coded before the main article, then the links in the right column will receive tab focus first before the links in the main article.

    You could change this by re-ordering your DOM, but oftentimes this is not possible. So, instead give the elements that should be the first ones to receive tab focus a positive @tabindex. The tab access will start at the smallest non-zero @tabindex value. If multiple elements share the same @tabindex value, these controls receive tab focus in DOM order. After that, interactive elements and those with @tabindex=0 will receive tab focus in DOM order.

    Example :

    The one thing that always annoys me the most is if the tab order in forms that I am supposed to fill in is illogical. Here is an example where the first and last name are separated by the address because they are in a table. We could fix it by moving to a <div> based layout, but let’s use @tabindex to demonstrate the change.

    Firstname :
    Address :
    Lastname :
    City :
    <table class="customtabs">
      <tr>
        <td>Firstname :
          <input type="text" id="firstname">
        </td>
        <td>Address :
          <input type="text" id="address">
        </td>
      </tr>
      <tr>
        <td>Lastname :
          <input type="text" id="lastname">
        </td>
        <td>City :
          <input type="text" id="city">
        </td>
      </tr>
    </table>
    
    Click here to test this form,
    then [TAB] :
    Firstname :
    Address :
    Lastname :
    City :
    <table class="customtabs">
      <tr>
        <td>Firstname :
          <input type="text" id="firstname" tabindex="10">
        </td>
        <td>Address :
          <input type="text" id="address" tabindex="30">
        </td>
      </tr>
      <tr>
        <td>Lastname :
          <input type="text" id="lastname" tabindex="20">
        </td>
        <td>City :
          <input type="text" id="city" tabindex="40">
        </td>
      </tr>
    </table>

    Be very careful with using non-zero tabindex values. Since they change the tab order on the page, you may get side effects that you might not have intended, such as having to give other elements on the page a non-zero tabindex value to avoid skipping too many other elements as I would need to do here.

    2.4. Focus on the right element

    Some of the controls that you create may be rather complex and open elements on the page that were previously hidden. This is particularly the case for drop-downs, pop-ups, and menus in general. Oftentimes the hidden element is not defined in the DOM right after the interactive control, such that a [TAB] will not put your keyboard focus on the next element that you are interacting with.

    The solution is to manage your keyboard focus from JavaScript using the .focus() method.

    Example :

    Here is a menu that is declared ahead of the menu button. If you tab onto the button and hit enter, the menu is revealed. But your tab focus is still on the menu button, so your next [TAB] will take you somewhere else. We fix it by setting the focus on the first menu item after opening the menu.

    &lt;script&gt;<br />
    function displayMenu(value) {<br />
    document.getElementById(&quot;custommenu&quot;).style.display=value;<br />
    }<br />
    &lt;/script&gt;
    <div id="custommenu" style="display:none ;">
      <button id="item1" onclick="displayMenu(’none’) ;">Menu item1</button>
      <button id="item2" onclick="displayMenu(’none’) ;">Menu item2</button>
    </div>
    <button onclick="displayMenu(’block’) ;">Menu</button>
    <script>
    function displayMenu(value) 
     document.getElementById("custommenu").style.display=value ;
    
    </script>
    
    &lt;script&gt;<br />
    function displayMenu2(value) {<br />
    document.getElementById(&quot;custommenu2&quot;).style.display=value;<br />
    document.getElementById(&quot;item1&quot;).focus();<br />
    }<br />
    &lt;/script&gt;
    <div id="custommenu" style="display:none ;">
      <button id="item1" onclick="displayMenu(’none’) ;">Menu item1</button>
      <button id="item2" onclick="displayMenu(’none’) ;">Menu item2</button>
    </div>
    <button onclick="displayMenu(’block’) ;">Menu</button>
    <script>
    function displayMenu(value) 
     document.getElementById("custommenu").style.display=value ;
     document.getElementById("item1").focus() ;
    
    </script>

    You will notice that there are still some things you can improve on here. For example, after you close the menu again with one of the menu items, the focus does not move back onto the menu button.

    Also, after opening the menu, you may prefer not to move the focus onto the first menu item but rather just onto the menu <div>. You can do so by giving that div a @tabindex and then calling .focus() on it. If you do not want to make the div part of the normal tabbing order, just give it a @tabindex=-1 value. This will allow your div to receive focus from script, but be exempt from accidental tabbing onto (though usually you just want to use @tabindex=0).

    Bonus : If you want to help keyboard users even more, you can also put outlines on the element that is currently in focus using CSS”s outline property. If you want to avoid the outlines for mouse users, you can dynamically add a class that removes the outline in mouseover events but leaves it for :focus.

    2.5. Provide sensible keyboard shortcuts

    At this stage your application is actually keyboard accessible. Congratulations !

    However, it’s still not very efficient : like power-users, screenreader users love keyboard shortcuts : can you imagine if you were forced to tab through an entire page, or navigate back to a menu tree at the top of the page, to reach each control you were interested in ? And, obviously, anything which makes navigating the app via the keyboard more efficient for screenreader users will benefit all power users as well, like the ubiquitous keyboard shortcuts for cut, copy and paste.

    HTML4 introduced so-called accesskeys for this. In HTML5 @accesskey is now allowed on all elements.

    The @accesskey attribute takes the value of a keyboard key (e.g. @accesskey="x") and is activated through platform- and browser-specific activation keys. For example, on the Mac it’s generally the [Ctrl] key, in IE it’ the [Alt] key, in Firefox on Windows [Shift]-[Alt], and in Opera on Windows [Shift]-[ESC]. You press the activation key and the accesskey together which either activates or focuses the element with the @accesskey attribute.

    Example :


    &lt;script&gt;<br />
    var button = document.getElementById('accessbutton');<br />
    if (button.accessKeyLabel) {<br />
     button.innerHTML += ' (' + button.accessKeyLabel + ')';<br />
    }<br />
    &lt;/script&gt;
    <button id="accessbutton" onclick="alert(’sent !’)" accesskey="e">
    Send
    </button>
    <script>
      var button = document.getElementById(’accessbutton’) ;
      if (button.accessKeyLabel) 
        button.innerHTML += ’ (’ + button.accessKeyLabel + ’)’ ;
      
    </script>

    Now, the idea behind this is clever, but the execution is pretty poor. Firstly, the different activation keys between different platforms and browsers make it really hard for people to get used to the accesskeys. Secondly, the key combinations can conflict with browser and screenreader shortcut keys, the first of which will render browser shortcuts unusable and the second will effectively remove the accesskeys.

    In the end it is up to the Web application developer whether to use the accesskey attribute or whether to implement explicit shortcut keys for the application through key event handlers on the window object. In either case, make sure to provide a help list for your shortcut keys.

    Also note that a page with a really good hierarchical heading layout and use of ARIA landmarks can help to eliminate the need for accesskeys to jump around the page, since there are typically default navigations available in screen readers to jump directly to headings, hyperlinks, and ARIA landmarks.

    3. Provide markup for AT

    Having made the application keyboard accessible also has advantages for screenreaders, since they can now reach the controls individually and activate them. So, next we will use a screenreader and close our eyes to find out where we only provide visual cues to understand the necessary interaction.

    Here are some of the issues to consider :

    • Role may need to get identified
    • States may need to be kept track of
    • Properties may need to be made explicit
    • Labels may need to be provided for elements

    This is where the W3C’s ARIA (Accessible Rich Internet Applications) standard comes in. ARIA attributes provide semantic information to screen readers and other AT that is otherwise conveyed only visually.

    Note that using ARIA does not automatically implement the standard widget behavior – you’ll still need to add focus management, keyboard navigation, and change aria attribute values in script.

    3.1. ARIA roles

    After implementing a custom interactive widget, you need to add a @role attribute to indicate what type of controls it is, e.g. that it is playing the role of a standard tag such as a button.

    Example :

    This menu button is implemented as a <div>, but with a role of “button” it is announced as a button by a screenreader.

    Menu
    <div tabindex="0" role="button">Menu</div>
    

    ARIA roles also describe composite controls that do not have a native HTML equivalent.

    Example :

    This menu with menu items is implemented as a set of <div> tags, but with a role of “menu” and “menuitem” items.

    <div role="menu">
      <div tabindex="0" role="menuitem">Cut</div>
      <div tabindex="0" role="menuitem">Copy</div>
      <div tabindex="0" role="menuitem">Paste</div>
    </div>
    

    3.2. ARIA states

    Some interactive controls represent different states, e.g. a checkbox can be checked or unchecked, or a menu can be expanded or collapsed.

    Example :

    The following menu has states on the menu items, which are here not just used to give an aural indication through the screenreader, but also a visual one through CSS.

    <style>
    .custombutton[aria-checked=true]:before 
       content :  "\2713 " ;
    
    </style>
    <div role="menu">
      <div tabindex="0" role="menuitem" aria-checked="true">Left</div>
      <div tabindex="0" role="menuitem" aria-checked="false">Center</div>
      <div tabindex="0" role="menuitem" aria-checked="false">Right</div>
    </div>
    

    3.3. ARIA properties

    Some of the functionality of interactive controls cannot be captured by the role attribute alone. We have ARIA properties to add features that the screenreader needs to announce, such as aria-label, aria-haspopup, aria-activedescendant, or aria-live.

    Example :

    The following drop-down menu uses aria-haspopup to tell the screenreader that there is a popup hidden behind the menu button together with an ARIA state of aria-expanded to track whether it’s open or closed.

    Justify
    &lt;script&gt;<br />
    var button = document.getElementById(&quot;button&quot;);<br />
    var menu = document.getElementById(&quot;menu&quot;);<br />
    var items = document.getElementsByClassName(&quot;menuitem&quot;);<br />
    var focused = 0;<br />
    function showMenu(evt) {<br />
       evt.stopPropagation();<br />
       menu.style.visibility = 'visible';<br />
       button.setAttribute('aria-expanded','true');<br />
       focused = getSelected();<br />
       items[focused].focus();<br />
     }<br />
     function hideMenu(evt) {<br />
       evt.stopPropagation();<br />
       menu.style.visibility = 'hidden';<br />
       button.setAttribute('aria-expanded','false');<br />
       button.focus();<br />
     }<br />
     function getSelected() {<br />
       for (var i=0; i &lt; items.length; i++) {<br />
         if (items[i].getAttribute('aria-checked') == 'true') {<br />
           return i;<br />
         }<br />
       }<br />
     }<br />
     function setSelected(elem) {<br />
       var curSelected = getSelected();<br />
       items[curSelected].setAttribute('aria-checked', 'false');<br />
       elem.setAttribute('aria-checked', 'true');<br />
     }<br />
     function selectItem(evt) {<br />
       setSelected(evt.target);<br />
       hideMenu(evt);<br />
     }<br />
    function getPrevItem(index) {<br />
       var prev = index - 1;<br />
       if (prev &lt; 0) {<br />
         prev = items.length - 1;<br />
       }<br />
       return prev;<br />
     }<br />
     function getNextItem(index) {<br />
       var next = index + 1;<br />
       if (next == items.length) {<br />
         next = 0;<br />
       }<br />
       return next;<br />
     }<br />
    function handleButtonKeys(evt) {<br />
       evt.stopPropagation();<br />
       var key = evt.keyCode;<br />
       switch(key) {<br />
         case (13): /* ENTER */<br />
         case (32): /* SPACE */<br />
           showMenu(evt);<br />
         default:<br />
       }<br />
     }<br />
     function handleMenuKeys(evt) {<br />
       evt.stopPropagation();<br />
       var key = evt.keyCode;<br />
       switch(key) {<br />
         case (38): /* UP */<br />
           focused = getPrevItem(focused);<br />
           items[focused].focus();<br />
           break;<br />
         case (40): /* DOWN */<br />
           focused = getNextItem(focused);<br />
           items[focused].focus();<br />
           break;<br />
         case (13): /* ENTER */<br />
         case (32): /* SPACE */<br />
           setSelected(evt.target);<br />
             hideMenu(evt);<br />
             break;<br />
         case (27): /* ESC */<br />
           hideMenu(evt);<br />
            break;<br />
         default:<br />
       }<br />
     }<br />
     button.addEventListener('click', showMenu, false);<br />
     button.addEventListener('keydown', handleButtonKeys, false);<br />
     for (var i = 0;  i &lt; items.length; i++) {<br />
       items[i].addEventListener('click', selectItem, false);<br />
       items[i].addEventListener('keydown', handleMenuKeys, false);<br />
     }<br />
    &lt;/script&gt;
    <div class="custombutton" id="button" tabindex="0" role="button"
       aria-expanded="false" aria-haspopup="true">
        <span>Justify</span>
    </div>
    <div role="menu"  class="menu" id="menu" style="display : none ;">
      <div tabindex="0" role="menuitem" class="menuitem" aria-checked="true">
        Left
      </div>
      <div tabindex="0" role="menuitem" class="menuitem" aria-checked="false">
        Center
      </div>
      <div tabindex="0" role="menuitem" class="menuitem" aria-checked="false">
        Right
      </div>
    </div>
    [CSS and JavaScript for example omitted]

    3.4. Labelling

    The main issue that people know about accessibility seems to be that they have to put alt text onto images. This is only one means to provide labels to screenreaders for page content. Labels are short informative pieces of text that provide a name to a control.

    There are actually several ways of providing labels for controls :

    • on img elements use @alt
    • on input elements use the label element
    • use @aria-labelledby if there is another element that contains the label
    • use @title if you also want a label to be used as a tooltip
    • otherwise use @aria-label

    I’ll provide examples for the first two use cases - the other use cases are simple to deduce.

    Example :

    The following two images show the rough concept for providing alt text for images : images that provide information should be transcribed, images that are just decorative should receive an empty @alt attribute.

    shocked lolcat titled 'HTML cannot do that!
    Image by Noah Sussman
    <img src="texture.jpg" alt="">
    <img src="lolcat.jpg"
    alt="shocked lolcat titled ’HTML cannot do that !">
    <img src="texture.jpg" alt="">
    

    When marking up decorative images with an empty @alt attribute, the image is actually completely removed from the accessibility tree and does not confuse the blind user. This is a desired effect, so do remember to mark up all your images with @alt attributes, even those that don’t contain anything of interest to AT.

    Example :

    In the example form above in Section 2.3, when tabbing directly on the input elements, the screen reader will only say "edit text" without announcing what meaning that text has. That’s not very useful. So let’s introduce a label element for the input elements. We’ll also add checkboxes with a label.






    <label>Doctor title :</label>
      <input type="checkbox" id="doctor"/>
    <label>Firstname :</label>
      <input type="text" id="firstname2"/>
    

    <label for="lastname2">Lastname :</label>
    <input type="text" id="lastname2"/>

    <label>Address :
    <input type="text" id="address2">
    </label>
    <label for="city2">City :
    <input type="text" id="city2">
    </label>
    <label for="remember">Remember me :</label>
    <input type="checkbox" id="remember">

    In this example we use several different approaches to show what a different it makes to use the <label> element to mark up input boxes.

    The first two fields just have a <label> element next to a <input> element. When using a screenreader you will not notice a difference between this and not using the <label> element because there is no connection between the <label> and the <input> element.

    In the third field we use the @for attribute to create that link. Now the input field isn’t just announced as "edit text", but rather as "Lastname edit text", which is much more useful. Also, the screenreader can now skip the labels and get straight on the input element.

    In the fourth and fifth field we actually encapsulate the <input> element inside the <label> element, thus avoiding the need for a @for attribute, though it doesn’t hurt to explicity add it.

    Finally we look at the checkbox. By including a referenced <label> element with the checkbox, we change the screenreaders announcement from just "checkbox not checked" to "Remember me checkbox not checked". Also notice that the click target now includes the label, making the checkbox not only more usable to screenreaders, but also for mouse users.

    4. Conclusions

    This article introduced a process that you can follow to make your Web applications accessible. As you do that, you will noticed that there are other things that you may need to do in order to give the best experience to a power user on a keyboard, a blind user using a screenreader, or a vision-impaired user using a screen magnifier. But once you’ve made a start, you will notice that it’s not all black magic and a lot can be achieved with just a little markup.

    You will find more markup in the WAI ARIA specification and many more resources at Mozilla’s ARIA portal. Now go and change the world !

    Many thanks to Alice Boxhall and Dominic Mazzoni for their proof-reading and suggested changes that really helped improve the article !