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• 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.

• FFMPEG Layering two .mov files color issue

  21 février 2023, par JDC

  I have two folders containing numbered .mov files all the same length, one folder for front and one for back. I'm using ffmpeg to combine the front and back videos with matching numbers into one output video (the front video has an alpha channel). The below command works, but in the output video the front layer has slightly incorrect colors compared to the input (reds are too yellow for example). The back layer in the output looks correct. Both input files use the bt709 color space (checked with ffprobe). Is there something in the overlay options which is causing the front layer to look incorrect, or something I'm doing wrong with the colorspace options ?

  


  


  for f in Video_Back/Video_Back_*.mov ; do
num=$(echo "$f" | sed -n 's/.*Video_Back_([0-9]5).mov$/\1/p')
if [ -f "Video_Front/Video_Front_$num.mov" ] ; then
ffmpeg -color_primaries bt709 -color_trc gamma28 -colorspace bt709 -i "$f" -color_primaries bt709 -color_trc gamma28 -colorspace bt709 -i "Video_Front/Video_Front_$num.mov" -filter_complex "[1:v]format=rgba[fg] ;[0:v][fg]overlay=shortest=1:alpha=straight,eq=gamma=1.0[mixed]" -map "[mixed]" -map 0:a:0 -c:v libx264 -crf 18 -preset veryfast -c:a copy "Video_Merged/Video_Merged_$num.mp4"
fi
done