[FFmpeg-devel] AC3 Format Detection unreliable.

Dan Sully daniel
Sun Aug 5 01:53:00 CEST 2007

* Justin Ruggles shaped the electrons to say...

>Doesn't look like that's an issue.  I'm getting the same thing on my 
>system.  The file is valid.  The issue seems to be the frame size. 
>640kbps 48kHz is the largest AC3 frame size, and I think it's not 
>fitting enough frames into the probe buffer to give a positive 
>detection.  I'll look into it.


FYI, the raw AC3 was originally in a Matroska container, using mkvextract to
pull it out. If I try and do my container conversion directly on the .mkv
file, ffmpeg spews tons of error messages about "non monotone timestamps",
but it identifies the ac3 stream properly:

Input #0, matroska, from 'foo.mkv':
  Duration: 01:36:34.4, start: 0.000000, bitrate: N/A
  Stream #0.0(eng): Video: h264, yuv420p, 1280x720, 24.39 fps(r)
  Stream #0.1(eng): Audio: liba52, 48000 Hz, 5:1
Output #0, avi, to 'foo.avi':
  Stream #0.0(eng): Video: libx264, yuv420p, 1280x720, q=2-31, 1000.00 fps(c)
  Stream #0.1(eng): Audio: ac3, 48000 Hz, 5:1

<dsully> please describe web 2.0 to me in 2 sentences or less.
<jwb> you make all the content. they keep all the revenue.

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