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• Subtitles in ffmpeg/libavfilter

  15 juin 2021, par Captain Jack

  I have a C program to read video/audio with libav/ffmpeg libraries and decode it.

  



  I am playing with some filters and most work just fine. I can draw text, overlay logos, flip and invert video colours. However, I am having big issues overlaying subtitles.

  



  My filter is very simple.

  



  const char *vfilter_descr = "[in]subtitles=subs.srt[out]";


  



  On the console I get this :

  



  [Parsed_subtitles_0 @ 0x7fe76c703240] Shaper: FriBidi 0.19.7 (SIMPLE) HarfBuzz-ng 2.4.0 (COMPLEX)
[Parsed_subtitles_0 @ 0x7fe76c703240] Using font provider coretext
[Parsed_subtitles_0 @ 0x7fe76c703240] fontselect: (Arial, 400, 0) -> /Library/Fonts/Microsoft/Arial.ttf, -1, ArialMT
[Parsed_subtitles_0 @ 0x7fe76c703240] fontselect: (Arial, 400, 100) -> /Library/Fonts/Microsoft/Arial Italic.ttf, -1, Arial-ItalicMT


  



  ...which somewhat confirms that subtitles are loading, though I am not sure why there are two fonts being loaded ?

  



  However, they are not showing at all - almost as if they never loaded. I tried several different files, including ASS ones but no luck.

  



  ffmpeg version is the latest one.

  



  $ ffmpeg -v
ffmpeg version 4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1.3_1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-11.0.2.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-11.0.2.jdk/Contents/Home/include/darwin' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-videotoolbox --disable-libjack --disable-indev=jack --enable-libaom --enable-libsoxr
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100


  



  Any ideas ?

  


• 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 ?

  


• JW Player fails with error with wma files : Task Queue failed at step 5

  17 mars 2018, par Sabeena

  I have a JW Player which plays MP3 files but with WMA files it gives the error :

  Task Queue failed at step 5: Playlist could not be loaded: Playlist file did not contain a valid playlist

  I thought of two reasons :

  1. There is no support for WMA but please confirm me this.
  2. Somewhere I need to setup the type of file I am using in this player.

  If WMA not supported in JW Player how can I play WMA and MP3 files in my website ?

  Is ffmpeg needed to convert WMA to MP3 while uploading ?