[MPlayer-users] Incorrect AMR Audio Playback Speed in 3GP Video

[Brendan Schwartz]

Hello,

I came across an issue with decoding AMR-NB audio. The audio seems to
play at twice the speed of the video. The audio track finishes playing
halfway through the video and as a result, MPlayer thinks the audio is
truncated.

Here's what I did:

I downloaded and installed amrnb-6.1.0.4 and amrwb-7.0.0.1 from
http://www.penguin.cz/~utx/amr as per the instructions in
libavcodec/libamr.c.

I downloaded and installed the 7/31 svn snapshot of MPlayer (just a
standard "./configure && make && sudo make install").

I downloaded and played
ftp://upload.mplayerhq.hu/MPlayer/samples/mobileVideo_3gp/ambiance.3gp
using "mplayer ambiance.3gp". I observed the audio track playing at
twice the speed of the video. This is through a terminal, so I didn't
actually see the video playing, but I was following along on the
command line.

After a few hours of googling and turning up nothing I reverted to
MPlayer 1.0RC1 and installed AMR NB and WB (floating point) using the
instructions in libavcodec/amr.c.
This resolved the problem -- the audio now plays in sync with the video.

I will also note that I installed a snapshot of FFmpeg (7/31) that
used the amr libraries from penguin.cz and it functioned correctly
(audio played at the correct speed).

This all took place on a 32bit P4 machine with a Ubuntu Edgy install.

I would like to dig deeper and help track down this issue, but I'm not
entirely sure how to proceed. Besides a binary search strategy for the
patch that broke this, what would the best way to locate the source of
this problem?

Thanks,
Brendan