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• WebRTC Stream Freezes When Picture Complexity Increases

  12 octobre 2021, par user1259576

  I am developing an application that uses WebRTC to display a live video stream being captured from a V4L2 source. The stream originates from a Linux box that has a DVI-USB capture card, is encoded to H264 by ffmpeg and sent to RTP, received by a Janus WebRTC server which is accessed by the web interface.

  


  Here is my current ffmpeg command - pretty simple :
ffmpeg -f v4l2 -i /dev/video0 -vf "transpose=1,scale=768:1024" -vcodec libx264 -profile:v baseline -pix_fmt yuv420p -f rtp rtp ://10.116.80.86:8004

  


  I can't go into details, but the DVI source generates a portrait 768x1024 image that initially is a simple image where the only movement is a small clock near the center that increments every second. At this stage, everything appears to work great. The image is high-quality and continuous/smooth in the browser.

  


  Once I interact with the DVI source, a more complex image is generated, with some text/lines in the upper half. Still not very complex - only 2 colors involved and some basic 1px line shapes, and only the little clock is moving. At this point, the video starts to freeze frequently, and only updates once in a while for a few seconds. Bandwidth should not be an issue here, and the bitrate appears to stay high. However, many fewer frames are decoded.

  


  I have also tried scaling the video down to 480x640 from 768x1024 and with that change the issue does not occur. However, I really need the full resolution and, again, there should not be a bandwidth issue here.

  


  I have also tried capturing the output of ffmpeg to a file rather than streaming to RTP and in the file everything is good.

  


  Here is a screenshot of the WebRTC internals (in Edge) for this stream. You can clearly see when the video image changes from the simple clock to including more shapes & text (nothing is changed here other than the image from the DVI source) :

  


  

  


  In Firefox, the video just freezes whenever frames are not decoded. In Edge, the video goes black after a moment with no frames decoded.

  


  Any ideas as to what might be causing this ?

  


• Revision f6582d6928 : Revert "Simplify mask checking in loop filters" Jingning saw bitstream change w

  4 décembre 2013, par Yunqing Wang

  Changed Paths :
   Modify /vp9/common/vp9_loopfilter.c

  
  
  Revert "Simplify mask checking in loop filters"

  Jingning saw bitstream change with this patch. It could be true
  that (mask_16x16_0 & 1) is 1, but (mask_16x16_1 & 1) is 0 in some
  edge cases.

  This reverts commit 8f05e70340533b9922be5b1c97c37e50607fd862.

  Change-Id : I0a529435ce816a1e14653eb510d5090de276070a

• Can ffmpeg write metadata encoder when transcoding alac/flac to aac audio file ?

  11 juin 2022, par David I

  I have a collection of alac and flac files from Bandcamp and an ffmpeg instance compiled with libfdk_aac https://trac.ffmpeg.org/wiki/CompilationGuide/Centos#libfdk_aac and am trying to convert these to lossy audio aac files for non-critical listening.

  


  With ffmpeg -i Liholesie\ -\ Shamanic\ Twilight\ -\ 09\ Gray\ Wings.m4a -c:a libfdk_aac -vbr 4 -c:v copy 09_Gray_wings_vbr4.m4a an expected aac .m4a audio file is produced, album art included, works well. There's one slight detail missing :

  


  During the ffmpeg conversion process ffmpeg says :

  


  Output #0, ipod, to '09_Gray_wings_vbr4.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: M4A isomiso2
    title           : Gray Wings
    artist          : Liholesie
    album_artist    : Liholesie
    album           : Shamanic Twilight
    comment         : Visit https://liholesie.bandcamp.com
    date            : 2021
    track           : 9
    encoder         : Lavf59.24.100
  Stream #0:0: Video: mjpeg (Baseline), yuvj444p(pc, bt470bg/unknown/unknown), 700x700 [SAR 72:72 DAR 1:1], q=2-31, 90k tbr, 90k tbn (attached pic)
  Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16 (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc59.33.100 libfdk_aac 
..




  


  and the file produced looks like that when ffprobed except that the Metadata : encoder field is missing :

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '09_Gray_wings_vbr4.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: M4A isomiso2
    title           : Gray Wings
    artist          : Liholesie
    album_artist    : Liholesie
    album           : Shamanic Twilight
    date            : 2021
    encoder         : Lavf59.24.100
    comment         : Visit https://liholesie.bandcamp.com
    track           : 9
  Duration: 00:06:57.78, start: 0.000000, bitrate: 155 kb/s
  Stream #0:0[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 152 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x0]: Video: mjpeg (Baseline), yuvj444p(pc, bt470bg/unknown/unknown), 700x700 [SAR 72:72 DAR 1:1], 90k tbr, 90k tbn (attached pic)


  


  Is there a way to write the encoder field in the Metadata section when transcoding (or is "encoder" not supported for aac m4a ? That would be weird since ffmpeg says what it says when specifying output during transcoding) .

  


  Any hints on how to write a self-defined text to said tag during transcoding are also welcome.