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• avformat/matroskaenc : Check for failure when writing SeekHead

  29 décembre 2019, par Andreas Rheinhardt

  avformat/matroskaenc : Check for failure when writing SeekHead
  mkv_write_seekhead() would up until now try to seek to the position where
  
  the SeekHead ought to be written, write the SeekHead and seek back. The
  
  first of these seeks was checked as was writing, yet the seek back was
  
  unchecked. Moreover the return value of mkv_write_seekhead() was unchecked
  
  (the ordinary return value was the position where the SeekHead was written).
  This commit changes this : Everything is checked. In the unseekable case
  
  (where the first seek may nevertheless work when it happens in the buffer)
  
  a failure at the first seek is not considered an error. In any case,
  
  failure to seek back is an error.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• ffplay won't with with more than 6 audio channels

  13 juin 2020, par Hiko Haieto

  I am trying to stream (raw) video and audio from a capture device as part of my home media setup (with my pc acting similarly to a receiver in a typical home theatre setup), but the biggest problem I haven't been able to get past is that I haven't been able to get ffplay to work with all 8 channels in 7.1 streams - two simply get dropped, despite it recognising 8 channel input or me specifying a 7.1 layout.

  



  I have been able to confirm that all 8 channels are present in the source by first using ffmpeg to save the output of a speaker test to a file and playing that back with both mplayer (which works) and ffplay (which doesn't). I might simply use mplayer if it weren't for the fact that piping output from ffmpeg adds too much latency for real-time use. I am using libSDL version 2.0.12 and ffplay 4.2.3, both of which are the latest at the time of writing and are ostensibly supposed to support 7.1 audio.

  



  Using output recorded from speaker-test -c 8, I am using the following to play it back in mplayer :

  



  mplayer -channels 8 -rawaudio channels=8 -format s16le -demuxer rawaudio speaker-test.pcm


  



  and the following to play it back in ffplay :

  



  ffplay -f s16le -ac 8 -af 'channelmap=channel_layout=7.1' speaker-test.pcm


  



  No matter what I try, ffplay is dropping the two side channels. Why might ffplay not be producing output for all 8 channels, and how might I fix it ?

  


• Recording OpenGL animation using apitrace and ffmpeg

  7 septembre 2017, par mikeglaz

  I created an OpenGL animation and would like to convert it to an mpeg-4 movie. I googled around and am using the following commands :

  apitrace trace ./solid

  When I play back using apitrace replay solid.trace everthing looks good. Then I try to convert to mp4 with :

  apitrace dump-images -o - solid.trace | ffmpeg -r 30 -f image2pipe -vcodec ppm -i pipe: -vcodec mpeg4 -y solid.mp4

  When I try to play back solid.mp4 I only see the first frame for a few seconds and then the image turns all pixelated. There is no animation.