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• avcodec/dovi_rpudec : implement limited DM decompression

  14 juillet 2024, par Niklas Haas

  avcodec/dovi_rpudec : implement limited DM decompression
  This implements the limited DM metadata compression scheme described in
  
  chapter 9 of the dolby vision bitstream specification.
  The spec is a bit unclear about how to handle the presence of static
  
  metadata inside compressed frames ; in that it doesn't explicitly forbid
  
  an encoder from repeating redundant metadata. In theory, we would need
  
  to detect this case and then strip the corresponding duplicate metadata
  
  from the existing set of static metadata. However, this is difficult to
  
  implement - esspecially for the case of metadata blocks which may be
  
  internally repeated (e.g. level 10).
  That said, the spec states outright that static metadata should be
  
  constant throughout the entire sequence, so a sane bitstream should not
  
  have any static metadata values changing from one frame to the next (at
  
  least up to a keyframe boundary), and therefore they should never be
  
  present in compressed frames. As a consequence, it makes sense to treat
  
  this as an error state regardless. (Ignoring them by default, or
  
  erroring if either AV_EF_EXPLODE or AV_EF_AGGRESSIVE are set)
  I was not able to find such samples in the wild (outside of artificially
  
  produced test cases for this exact scenario), so I don't think we need
  
  to worry about it until somebody produces one.
  

  • [DH] libavcodec/dovi_rpudec.c

• Command-line streaming webcam with audio from Ubuntu server in WebM format

  28 avril 2017, par mjtb

  I am trying to stream video and audio from my webcam connected to my headless Ubuntu server (running Maverick 10.10). I want to be able to stream in WebM format (VP8 video + OGG). Bandwidth is limited, and so the stream must be below 1Mbps.

  I have tried using FFmpeg. I am able to record WebM video from the webcam with the following :

  ffmpeg -s 640x360 \
  
  -f video4linux2 -i /dev/video0 -isync -vcodec libvpx -vb 768000 -r 10 -vsync 1 \
  
  -f alsa -ac 1 -i hw:1,0 -acodec libvorbis -ab 32000 -ar 11025 \
  
  -f webm /var/www/telemed/test.webm 

  However despite experimenting with all manner of vsync and async options, I can either get out of sync audio, or Benny Hill style fast-forward video with matching fast audio. I have also been unable to get this actually working with ffserver (by replacing the test.webm path and filename with the relevant feed filename).

  The objective is to get a live, audio + video feed which is viewable in a modern browser, in a tight bandwidth, using only open-source components. (None of that MP3 format legal chaff)

  My questions are therefore :
  How would you go about streaming webm from a webcam via Linux with in-sync audio ? What software you use ?

  Have you succeeded in encoding webm from a webcam with in-sync audio via FFmpeg ? If so, what command did you issue ?

  Is it worth persevering with FFmpeg + FFserver, or are there other more suitable command-line tools around (e.g. VLC which doesn’t seem too well built for encoding) ?

  Is something like Gstreamer + flumotion configurable from the command line ? If so, where do I find command line documentation because flumotion doc is rather light on command line details ?

  Thanks in advance !

• Command-line streaming webcam with audio from Ubuntu server in WebM format

  6 avril, par mjtb

  I am trying to stream video and audio from my webcam connected to my headless Ubuntu server (running Maverick 10.10). I want to be able to stream in WebM format (VP8 video + OGG). Bandwidth is limited, and so the stream must be below 1Mbps.

  



  I have tried using FFmpeg. I am able to record WebM video from the webcam with the following :

  



  ffmpeg -s 640x360 \
-f video4linux2 -i /dev/video0 -isync -vcodec libvpx -vb 768000 -r 10 -vsync 1 \
-f alsa -ac 1 -i hw:1,0 -acodec libvorbis -ab 32000 -ar 11025 \
-f webm /var/www/telemed/test.webm 


  



  However despite experimenting with all manner of vsync and async options, I can either get out of sync audio, or Benny Hill style fast-forward video with matching fast audio. I have also been unable to get this actually working with ffserver (by replacing the test.webm path and filename with the relevant feed filename).

  



  The objective is to get a live, audio + video feed which is viewable in a modern browser, in a tight bandwidth, using only open-source components. (None of that MP3 format legal chaff)

  



  My questions are therefore :
How would you go about streaming webm from a webcam via Linux with in-sync audio ? What software you use ?

  



  Have you succeeded in encoding webm from a webcam with in-sync audio via FFmpeg ? If so, what command did you issue ?

  



  Is it worth persevering with FFmpeg + FFserver, or are there other more suitable command-line tools around (e.g. VLC which doesn't seem too well built for encoding) ?

  



  Is something like Gstreamer + flumotion configurable from the command line ? If so, where do I find command line documentation because flumotion doc is rather light on command line details ?

  



  Thanks in advance !