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• Chrome’s New Audio Notifier

  30 janvier 2014, par Multimedia Mike — General

  Version 32 of Google’s Chrome web browser introduced this nifty feature :

  
  
  

  When a browser tab has an element that is producing audio, the browser’s tab shows the above audio notification icon to inform the user. I have seen that people have a few questions about this, specifically :

  1. How does this feature work ?
  2. Why wasn’t this done sooner ?
  3. Are other browsers going to follow suit ?

  Short answers : 1) Chrome offers a new plugin API that the Flash Player is now using, as are Chrome’s internal media playing facilities ; 2) this feature was contingent on the new plugin infrastructure mentioned in the previous answer ; 3) other browsers would require the same infrastructure support.

  Longer answers follow…

  Plugin History
  Plugins were originally based on the Netscape Plugin API. This was developed in the early 1990s in order to support embedding PDFs into the Netscape web browser. The NPAPI does things like providing graphics contexts for drawing and input processing, and mediate network requests through the browser’s network facilities.

  What NPAPI doesn’t do is handle audio. In the early-mid 1990s, audio support was not a widespread consideration in the consumer PC arena. Due to the lack of audio API support, if a plugin wanted to play audio, it had to go outside of the plugin framework.

  
  
  

  There are a few downsides to this approach :

  • If a plugin wants to play audio, it needs to access unique audio APIs on each supported platform. One of the most famous things I’ve ever written deals concerns this nightmare on Linux. (The picture worth a thousand words.)
  • Plugin necessarily needs free unrestricted access to system facilities, i.e., security measures like sandboxing become more difficult without restricting functionality.
  • Since the browser doesn’t mediate access to the audio APIs, the browser can’t reasonably be expected to know when a plugin is accessing the audio resources.

  So that last item hopefully answers the question of why it has been so difficult for NPAPI-supporting browsers to implement what seems like it would be simple functionality, like implementing a per-tab audio notifier.

  Plugin Future
  Since Google released Chrome in an effort to facilitate advancements on the client side of the internet, they have made numerous efforts to modernize various legacy aspects of web technology. These efforts include the SPDY protocol, Native Client, WebM/WebP, and something call the Pepper Plugin API (PPAPI). This is a more modern take on the classic plugin architecture to supplant the aging NPAPI :

  
  
  

  Right away, we see that the job of the plugin writer is greatly simplified. Where was this API years ago when I was writing my API jungle piece ?

  The Linux version of Chrome was apparently the first version that packaged the Pepper version of the Flash Player (doing so fixed an obnoxious bug in the Linux Flash Player interaction with GTK). Now, it looks like Windows and Mac have followed suit. Digging into the Chrome directory on a Windows 7 installation :

  AppData\Local\Google\Chrome\Application[version]\PepperFlash\pepflashplayer.dll

  This directory exists for version 31 as well, which is still hanging around my system.

  So, to re-iterate : Chrome has a new plugin API that plugins use to access the audio API. Chrome knows when the API is accessed and that allows the browser to display the audio notifier on a tab.

  Other Browsers
  What about other browsers ? “Mozilla is not interested in or working on Pepper at this time. See the Chrome Pepper pages.”

• Calculate VMAF score while encoding a video with FFmpeg

  31 octobre 2024, par user8071576

  I have an ffmpeg version built with VMAF library. I can use it to calculate the VMAF scores of a distorted video against a reference video using commands like this :

  


  ffmpeg -i distorted.mp4 -i original.mp4 -filter_complex "[0:v]scale=640:480:flags=bicubic[main];[main][1:v]libvmaf=model_path=model/vmaf_v0.6.1.json:log_path=log.json" -f null -


  


  Now, I remember there was a way to get VMAF scores while performing regular ffmpeg encoding. How can I do that at the same time ?

  


  I want to encode a video like this, while also calulate the VMAF of the output file :

  


  ffmpeg -i original.mp4 -crf 27 -s 640x480 out.mp4


  


• Python : Extracting device and lens information from video metadata

  14 mai 2023, par cat_got_my_tongue

  I am interested in extracting device and lens information from videos. Specifically, make and model of the device and the focal length. I was able to do this successfully for still images using the exifread module and extract a whole bunch of very useful information :

  


  image type      : MPO
Image ImageDescription: Shot with DxO ONE
Image Make: DxO
Image Model: DxO ONE
Image Orientation: Horizontal (normal)
Image XResolution: 300
Image YResolution: 300
Image ResolutionUnit: Pixels/Inch
Image Software: V3.0.0 (2b448a1aee) APP:1.0
Image DateTime: 2022:04:05 14:53:45
Image YCbCrCoefficients: [299/1000, 587/1000, 57/500]
Image YCbCrPositioning: Centered
Image ExifOffset: 158
Thumbnail Compression: JPEG (old-style)
Thumbnail XResolution: 300
Thumbnail YResolution: 300
Thumbnail ResolutionUnit: Pixels/Inch
Thumbnail JPEGInterchangeFormat: 7156
Thumbnail JPEGInterchangeFormatLength: 24886
EXIF ExposureTime: 1/3
EXIF FNumber: 8
EXIF ExposureProgram: Aperture Priority
EXIF ISOSpeedRatings: 100
EXIF SensitivityType: ISO Speed
EXIF ISOSpeed: 100
EXIF ExifVersion: 0221
EXIF DateTimeOriginal: 2022:04:05 14:53:45
EXIF DateTimeDigitized: 2022:04:05 14:53:45
EXIF ComponentsConfiguration: CrCbY
EXIF CompressedBitsPerPixel: 3249571/608175
EXIF ExposureBiasValue: 0
EXIF MaxApertureValue: 212/125
EXIF SubjectDistance: 39/125
EXIF MeteringMode: MultiSpot
EXIF LightSource: Unknown
EXIF Flash: Flash did not fire
EXIF FocalLength: 1187/100
EXIF SubjectArea: [2703, 1802, 675, 450]
EXIF MakerNote: [68, 88, 79, 32, 79, 78, 69, 0, 12, 0, 0, 0, 21, 0, 3, 0, 5, 0, 2, 0, ... ]
EXIF SubSecTime: 046
EXIF SubSecTimeOriginal: 046
EXIF SubSecTimeDigitized: 046
EXIF FlashPixVersion: 0100
EXIF ColorSpace: sRGB
EXIF ExifImageWidth: 5406
EXIF ExifImageLength: 3604
Interoperability InteroperabilityIndex: R98
Interoperability InteroperabilityVersion: [48, 49, 48, 48]
EXIF InteroperabilityOffset: 596
EXIF FileSource: Digital Camera
EXIF ExposureMode: Auto Exposure
EXIF WhiteBalance: Auto
EXIF DigitalZoomRatio: 1
EXIF FocalLengthIn35mmFilm: 32
EXIF SceneCaptureType: Standard
EXIF ImageUniqueID: C01A1709306530020220405185345046
EXIF BodySerialNumber: C01A1709306530


  


  Unfortunately, I have been unable to extract this kind of info from videos so far.

  


  This is what I have tried so far, with the ffmpeg module :

  


  import ffmpeg
from pprint import pprint

test_video = "my_video.mp4"
pprint(ffmpeg.probe(test_video)["streams"])


  


  And the output I get contains a lot of info but nothing related to the device or lens, which is what I am looking for :

  


  [{'avg_frame_rate': '30/1',
  'bit_rate': '1736871',
  'bits_per_raw_sample': '8',
  'chroma_location': 'left',
  'codec_long_name': 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10',
  'codec_name': 'h264',
  'codec_tag': '0x31637661',
  'codec_tag_string': 'avc1',
  'codec_time_base': '1/60',
  'codec_type': 'video',
  'coded_height': 1088,
  'coded_width': 1920,
  'display_aspect_ratio': '16:9',
  'disposition': {'attached_pic': 0,
                  'clean_effects': 0,
                  'comment': 0,
                  'default': 1,
                  'dub': 0,
                  'forced': 0,
                  'hearing_impaired': 0,
                  'karaoke': 0,
                  'lyrics': 0,
                  'original': 0,
                  'timed_thumbnails': 0,
                  'visual_impaired': 0},
  'duration': '20.800000',
  'duration_ts': 624000,
  'has_b_frames': 0,
  'height': 1080,
  'index': 0,
  'is_avc': 'true',
  'level': 40,
  'nal_length_size': '4',
  'nb_frames': '624',
  'pix_fmt': 'yuv420p',
  'profile': 'Constrained Baseline',
  'r_frame_rate': '30/1',
  'refs': 1,
  'sample_aspect_ratio': '1:1',
  'start_pts': 0,
  'start_time': '0.000000',
  'tags': {'creation_time': '2021-05-08T13:23:20.000000Z',
           'encoder': 'AVC Coding',
           'handler_name': 'VideoHandler',
           'language': 'und'},
  'time_base': '1/30000',
  'width': 1920},
 {'avg_frame_rate': '0/0',
  'bit_rate': '79858',
  'bits_per_sample': 0,
  'channel_layout': 'stereo',
  'channels': 2,
  'codec_long_name': 'AAC (Advanced Audio Coding)',
  'codec_name': 'aac',
  'codec_tag': '0x6134706d',
  'codec_tag_string': 'mp4a',
  'codec_time_base': '1/48000',
  'codec_type': 'audio',
  'disposition': {'attached_pic': 0,
                  'clean_effects': 0,
                  'comment': 0,
                  'default': 1,
                  'dub': 0,
                  'forced': 0,
                  'hearing_impaired': 0,
                  'karaoke': 0,
                  'lyrics': 0,
                  'original': 0,
                  'timed_thumbnails': 0,
                  'visual_impaired': 0},
  'duration': '20.864000',
  'duration_ts': 1001472,
  'index': 1,
  'max_bit_rate': '128000',
  'nb_frames': '978',
  'profile': 'LC',
  'r_frame_rate': '0/0',
  'sample_fmt': 'fltp',
  'sample_rate': '48000',
  'start_pts': 0,
  'start_time': '0.000000',
  'tags': {'creation_time': '2021-05-08T13:23:20.000000Z',
           'handler_name': 'SoundHandler',
           'language': 'und'},
  'time_base': '1/48000'}]


  


  Are these pieces of info available for videos ? Should I be using a different package ?

  


  Thanks.

  


  Edit :

  


  pprint(ffmpeg.probe(test_video)["format"]) gives

  


  {'bit_rate': '1815244',
 'duration': '20.864000',
 'filename': 'my_video.mp4',
 'format_long_name': 'QuickTime / MOV',
 'format_name': 'mov,mp4,m4a,3gp,3g2,mj2',
 'nb_programs': 0,
 'nb_streams': 2,
 'probe_score': 100,
 'size': '4734158',
 'start_time': '0.000000',
 'tags': {'artist': 'Microsoft Game DVR',
          'compatible_brands': 'mp41isom',
          'creation_time': '2021-05-08T12:12:33.000000Z',
          'major_brand': 'mp42',
          'minor_version': '0',
          'title': 'Snipping Tool'}}