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• Write webcam video with avconv

  31 juillet 2012, par Jones

  Have problem to write video avi with avconv

  I try using

  avconv -v debug -f video4linux2 -i /dev/video1 frontal.avi

  but video not correct. I see this line [video4linux2 @ 0x8100b00] The v4l2 frame is 8160 bytes, but 614400 bytes are expected and I don't identify options to correct this.

  Output of debug

  avconv version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  
    built on Jun 12 2012 16:37:58 with gcc 4.6.3
  
    configuration: --extra-version='4:0.8.3-0ubuntu0.12.04.1' --arch=i386 --prefix=/usr --libdir=/usr/lib/i386-linux-gnu --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --enable-libvpx --enable-runtime-cpudetect --enable-libfreetype --enable-vaapi --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --shlibdir=/usr/lib/i386-linux-gnu/i686/cmov --cpu=i686 --enable-shared --disable-static
  
    libavutil    51. 22. 1 / 51. 22. 1
  
    libavcodec   53. 35. 0 / 53. 35. 0
  
    libavformat  53. 21. 0 / 53. 21. 0
  
    libavdevice  53.  2. 0 / 53.  2. 0
  
    libavfilter   2. 15. 0 /  2. 15. 0
  
    libswscale    2.  1. 0 /  2.  1. 0
  
    libpostproc  52.  0. 0 / 52.  0. 0
  
  [video4linux2 @ 0x8100b00] [3]Capabilities: 4000001
  
  [video4linux2 @ 0x8100b00] Querying the device for the current frame size
  
  [video4linux2 @ 0x8100b00] Setting frame size to 640x480
  
  [video4linux2 @ 0x8100b00] The V4L2 driver set input_id: 0, input: Camera 1
  
  [video4linux2 @ 0x8100b00] The v4l2 frame is 8160 bytes, but 614400 bytes are expected
  
  [rawvideo @ 0x8102920] err{or,}_recognition separate: 1; 1
  
  [rawvideo @ 0x8102920] err{or,}_recognition combined: 1; 1
  
  [video4linux2 @ 0x8100b00] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, video4linux2, from '/dev/video1':
  
    Duration: N/A, bitrate: 147456 kb/s
  
      Stream #0.0, 0, 1/1000000: Video: rawvideo, yuyv422, 640x480, 1/30, 147456 k
  
  File 'frontal.avi' already exists. Overwrite ? [y/N] y
  
  Incompatible pixel format 'yuyv422' for codec 'mpeg4', auto-selecting format 'yu
  
  [buffer @ 0x81020c0] w:640 h:480 pixfmt:yuyv422
  
  [avsink @ 0x81022a0] auto-inserting filter 'auto-inserted scaler 0' between the
  
  [scale @ 0x81026e0] w:640 h:480 fmt:yuyv422 -> w:640 h:480 fmt:yuv420p flags:0x4
  
  [mpeg4 @ 0x81019a0] err{or,}_recognition separate: 1; 1
  
  [mpeg4 @ 0x81019a0] err{or,}_recognition combined: 1; 1
  
  [mpeg4 @ 0x81019a0] detected 1 logical cores
  
  [mpeg4 @ 0x81019a0] Unsupported bit depth: 0
  
  [rawvideo @ 0x8102920] err{or,}_recognition separate: 1; 1
  
  [rawvideo @ 0x8102920] err{or,}_recognition combined: 1; 1
  
  Output #0, avi, to 'frontal.avi':
  
    Metadata:
  
      ISFT            : Lavf53.21.0
  
      Stream #0.0, 0, 1/30: Video: mpeg4, yuv420p, 640x480, 1/30, q=2-31, 200 kb/s

• Why does my Blink based browser play hide and seek ?

  21 janvier 2016, par Caius Jard

  We have a C# tool (that I wrote) that records online broadcasts taking place a custom written (that we wrote) flash app. (There are no DRM or copyright issues here.)

  We’ve coded up a system whereby this tool is installed on a Windows Server 2012 R2 Amazon AWS instance. After we boot the instance, the tool loads, waits for the right time to start recording, launches a browser and passes the command line argument of the URL to access the broadcast. The browser will then load the flash app and the interview audio and video will start arriving at the browser instance on AWS

  By way of a virtual audio cable driver, screen / audio capture directshow filters and ffmpeg a screen recording is taken. The C# tool calls ffmpeg and ffmpeg will record the screen reliably for the entire interview, then the tool shuts the whole thing down

  The problem I’m having is that both Chrome and Electron browser sometimes simply don’t draw themselves on the screen so all ffmpeg ends up recording is a blank desktop and the audio of the broadcast (hence, the browser IS running)

  We found this out when recordings started turning up with X hours of merely recording the windows desktop and the tool’s main window with a countdown timer.

  A screenshotting facility was built into the tool and added to its web control interface, and this way we can test whether the browser is visible - a human looks at the screenshot of every broadcast, just after recording has started (the browser is supposed to be on show by this time)

  We notice that 50% of the time, the browser isn’t drawing itself on screen. By 50% I mean that every other recording that the AWS instance carries out, will be blank : AWS starts, records ok, shuts down. AWS starts again an hour later for a different broadcast, recording is blank, shuts down.. Starts/ok/shutdown. Starts/blank/shutdown. Repeat ad infinitum

  What’s even more strange is that if I run VNCviewer on my dev machine and connect up to an instance that is having a problem, the instant that the VNC connection is up and the remote desktop is showing on my screen, the browser suddenly appears as if nothing was ever wrong. A screenshot from before the VNC connect shows blank desktop, connect VNC, take another screenshot and the browser is there. All through it the audio is fine - the browser connected to the boadcast is fine, for sure

  It’s as though Chrome/Electron thinks "you know what, noone is looking at me so I’m not going to bother drawing myself". No screen saver is set, though the power plan has the setting "turn off the display after 15 minutes".

  Perhaps Chrome/Electron have a test amounts to "if the display is off, don’t draw". I can’t explain the inconsistency though - the recorder launches at least 1 hour before it’s needed, and sits there idle until it’s time to start the browser. You’d hence imagine that the "power off the monitor after 15 mins" setting would reliably have ensured the "monitor" is "off" by the time every recording start comes around

  This behaviour doesn’t happen with any of the other browsers (but unfortunately the app doesn’t and cannot work in them because it uses some weird chrome-only technology/API).

  Can anyone suggest anything to look at to help debug this, or anything I can build into the C# tool to overcome the problem ? Coding it up to connect to itself via VNC for a few seconds after it has launched the browser.. Well that just tastes nasty.

  Naturally, as soon as I connect to the machine via VNC (rather than RDP - RDP isn’t usable because the recording context is in a logged on session for a particular user) the problem goes away, which makes it frustratingly hard to debug.

• Screen capture with libavcodec/ffmpeg, and write it to mp4 file

  10 février 2015, par Drakkainen

  I’m trying to (programatically) record the screen with DirectShow screen driver. I wrote some quick and (very) dirty code to try to get that to work (http://pastebin.com/ZJuhZRCz) based on ffmpeg examples but I have lots of trouble figuring out what time_base/framerate to use. If i leave the time_base/framerate parts empty I only get a single still frame. If i change them to any values, the video just turns black.

  I’m guessing it has something to do with the output file settings, but I just ran out of ideas on what to try. Any pointers/help would be greatly appreciated.