[FFmpeg-user] amix with atempo: Inconsistent behaviour creating m4a with aac

Pavel Koshevoy pkoshevoy at gmail.com
Wed Sep 13 15:08:48 EEST 2017

On Sep 13, 2017 4:32 AM, "Jonathan Girven" <jonathan.girven at trickbook.com>

I am trying to take the audio from two mp4 files, merge them together one
after the other (perhaps with some other effects such as a fade transition:
not shown), and apply atempo to the result.

I am working with the current FFmpeg git master branch. I have attached an
example file to reproduce the issue with:  BigBuckBunny_320x180_t10.mp4
<http://www.ffmpeg-archive.org/file/t377720/BigBuckBunny_320x180_t10.mp4>  .
And here is the command and output:

$ ffmpeg -y \
  -i BigBuckBunny_320x180_t10.mp4 \
  -i BigBuckBunny_320x180_t10.mp4 \
  -filter_complex "
" \
  -map [com_a_slomo] \
  -c:a aac \

I haven't tested such use case, but I can tell you atempo also changes
output pts (computes it based on the number of samples output so far).  So
shouldn't mix_audio2 asetpts expression reference the output of atempo for


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