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• How can I correctly provide a mock webcam video to Chrome ?

  15 décembre 2022, par doppelgreener

  I'm trying to run end-to-end testing in Chrome for a product that requires a webcam feed halfway through to operate. From what I understand this means providing a fake webcam video to Chrome using the --use-file-for-fake-video-capture="/path/to/video.y4m" command line argument. It will then use that as a webcam video.

  



  However, no matter what y4m file I provide, I get the following error from Chrome running under these conditions :

  



  DOMException: Could not start video source
{
  code: 0,
  message: "Could not start video source",
  name: "NotReadableError"
}


  



  Notably I can provide an audio file just fine using --use-file-for-fake-audio-capture and Chrome will work with it well. The video has been my sticking point.

  



  This error comes out of the following straightforward mediaDevices request :

  



  navigator.mediaDevices.getUserMedia({ video: true, audio: true })
  .then(data => {
    // do stuff
  })
  .catch(err => {
    // oh no!
  });


  



  (This always hits the “oh no !” branch when a video file is provided.)

  



  What I've tried so far

  



  I've been running Chrome with the following command line arguments (newlines added for readability), and I'm using a Mac hence the open command :

  





  open -a "Google Chrome" --args
  --disable-gpu
  --use-fake-device-for-media-stream
  --use-file-for-fake-video-capture="~/Documents/mock/webcam.y4m"
  --use-file-for-fake-audio-capture="~/Documents/mock/microphone.wav"


  



  webcam.y4m and microphone.wav were generated from a video file I recorded.

  



  I first recorded a twenty-second mp4 video using my browser's MediaRecorder, downloaded the result, and converted it using the following command line commands :

  



  ffmpeg -y -i original.mp4 -f wav -vn microphone.wav
ffmpeg -y -i original.mp4 webcam.y4m


  



  When this didn't work, I tried the same using a twenty-second movie file I recorded in Quicktime :

  



  ffmpeg -y -i original.mov -f wav -vn microphone.wav
ffmpeg -y -i original.mov webcam.y4m


  



  When that also failed, I went straight to the Chromium file that explains fake video capture, went to the example y4m file list it provided, and downloaded the grandma file and provided that as a command line argument to Chrome instead :

  



  open -a "Google Chrome" --args
  --disable-gpu
  --use-fake-device-for-media-stream
  --use-file-for-fake-video-capture="~/Documents/mock/grandma_qcif.y4m"
  --use-file-for-fake-audio-capture="~/Documents/mock/microphone.wav"


  



  Chrome provides me with the exact same error in all of these situations.

  



  The only time Chrome doesn't error out with that mediaDevices request is when I omit the video completely :

  



  open -a "Google Chrome" --args
  --disable-gpu
  --use-fake-device-for-media-stream
  --use-file-for-fake-audio-capture="~/Documents/mock/microphone.wav"


  



  Accounting for C420mpeg2

  



  TestRTC suggests Chrome will “crash” if I give it a C420mpeg2 file, and recommends that simply replacing the metadata fixes the issue. Indeed the video file I generate from ffmpeg gives me the following header :

  



  YUV4MPEG2 W1280 H720 F30:1 Ip A1:1 C420mpeg2 XYSCSS=420MPEG2


  



  Chrome doesn't actually crash when run with this file, I just get the error above. If I edit the video file to the following header though per TestRTC's recommendations I get the same situation :

  



  YUV4MPEG2 W1280 H720 F30:1 Ip A1:1 C420 XYSCSS=420MPEG2


  



  The video file still gives me the above error in these conditions.

  



  What can/should I do ?

  



  How should I be providing a video file to Chrome for this command line argument ?

  



  How should I be recording or creating the video file ?

  



  How should I convert it to y4m ?

  


• Revert "avcodec/decode : copy the output parameters from the last bsf in the chain...

  12 septembre 2018, par James Almer

  Revert "avcodec/decode : copy the output parameters from the last bsf in the chain back to the AVCodecContext"
  This reverts commit f631c328e680a3dd491936b92f69970c20cdcfc7.
  The avcodec_parameters_to_context() call was freeing and reallocating
  
  AVCodecContext->extradata, essentially taking ownership of it, which according
  
  to the doxy is user owned. This is an API break and has produced crashes in
  
  some library users like Firefox[1].
  Revert until a better solution is found to internally propagate the filtered
  
  extradata back into the decoder context, or a decision is made to change the
  
  API.
  [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1486080
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/decode.c

• Revert "decode : copy the output parameters from the last bsf in the chain back to...

  12 septembre 2018, par James Almer

  Revert "decode : copy the output parameters from the last bsf in the chain back to the AVCodecContext"
  This reverts commit 662558f985f50834eebe82d6b6854c66f33ab320.
  The avcodec_parameters_to_context() call was freeing and reallocating
  
  AVCodecContext->extradata, essentially taking ownership of it, which according
  
  to the doxy is user owned. This is an API break and has produces crashes in
  
  some library users like Firefox.
  
  Revert until a better solution is found to internally propagate the filtered
  
  extradata back into the decoder context.
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DBH] libavcodec/decode.c