[Libav-user] Seeking in VBR MP3 file
pasanen.tuukka at gmail.com
Sun Oct 27 18:24:37 CET 2013
I'm trying to make Mixxx (http://mixxx.org) input FFmpeg plugin to function
again. Now it works with Libav 0.8/9 (they work perfectly) and FFmpeg 0.11
but version above that (like 1.0-2.0/Git) doesn't work as they should with
MP3 (Ogg/Vorbis, MP4 works like a charm). Problem is that Mixxx reading
should be Byte exact so one should know PCM point of time.
Problem appears in two ways: If one jumps in some X PTS in VBR (mostly VBR
4) MP3 file and then position tries to find PTS/DTS it ain't same as
reading with ffprobe -show_frames (All PTS dividable with 4608 like they
should?). Biggest problem is reading backwards in some X PTS then PTS
around jumps without any system (I think Xing headers points).
I have made small application/project in Github that shows the problem:
https://github.com/illuusio/ffmpeg-example.git (Sorry for debug output).
As I said this one source code works seamlessly with FFmpeg 0.11 and Libav
0.8/9/Git so I thought I'm doing something really wrong with FFmpeg 1.0 and
above. For testing any VBR MP3 will do fine. I have used for testing random
Jamendo files like:
One should import created pcm files (out-for.pcm is Forward played file and
out-rev.pcm is same played backwards order) in Audacity and try to listen
them to notice what is wrong.
I someone have more knowledge about because I have been struggling with
this many months..
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