[MPlayer-advusers] mp3 decoding problem

[The Wanderer]

compn wrote:

> On Wed, 26 Oct 2005 14:51:14 -0400
> The Wanderer <inverseparadox at comcast.net> wrote:
> 
>> The Wanderer wrote:
>> 
>>> compn wrote:
>>> 
>>>> decoding this file causes audio glitches in mplayer
>>>> -demuxer 35, -ac ffmp3, -dumpaudio, nothing helps
>>>> user reports it playing fine in xine.
> 
> this is incorrect, i found if you combine such commandlines, you can
> play the audio correctly in mplayer, i figured this out by studying
> how vlc would do it
> 
> mplayer 163.mp4 -demuxer 35 -ac +ffmp3
> 
> but i'm told that the video speeds up/plays incorrectly

It does; if you also specify '-fps 24000/1001' it will play back
perfectly. I've seen this discussed on the forums of the people who
released the files, and hadn't reached the point of thinking to post it
here.

> at least this gives you correct audio. altho i'm at a loss at why
> ffmp3 is not handling mp3 audio when demuxed with lavf... old
> codecs.conf or missing entry?

For one thing, the audio in the file is misdetected by FFmpeg - it
thinks that it's AAC for some reason. (Probably to do with the fact that
the audio ID tag in that file - the same data you set with '-fafmttag' -
is some eight to sixteen hex digits long, rather than what the MPlayer
man page claims is the MP3 standard of '0x55'.)

There is an MPlayer bug, in the demuxer; there is also an FFmpeg bug, in
the audio-format detection; there may also be a bug in whatever program
created the files, in the audio-format tag writing. Stack the two (or
three) of them together and you get a metaphorical perfect storm. (It
doesn't help that there doesn't appear to be any way to force FFmpeg to
use a particular codec when decoding, unlike with MPlayer... at least,
none of the things I've tried have worked right.)

>>> I have the what is almost certainly the same file (~233MB in
>>> total), and have experienced a number of different problems with
>>> it
>> 
>> I'll note that there are now two of these files that I know of,
>> from the same source, both exhibiting very similar problems
>> (although, from my limited examination, the second less so than the
>> first). For the time being, there are also working XviD/AVI
>> versions being released in parallel to the problematic x264/MP4
>> versions, but that will not be the case for much longer.
> 
> if you would talk to the guys encoding this, find out what program
> they use, etc, it would be useful, can we claim broken encoder yet?
> hehe

I've tried to contact them, with no real luck so far (although there are
avenues still available - f'rinstance, no big-name people were there in
their IRC channel last time I tried). I vaguely seem to remember a
report, quite some time back when they were still using AVI, that they
were doing their encoding and muxing with either MEncoder or FFmpeg...
but that does not seem likely at this juncture.

> i've had a 3-4 users come in #mplayer and ask about this problem...

I've seen at least one of them on the forums I mentioned, so yes, I'm
aware of that.

...I think there was something else I wanted to say in here, but I don't
remember offhand what it was.

-- 
       The Wanderer

Warning: Simply because I argue an issue does not mean I agree with any
side of it.

Secrecy is the beginning of tyranny.