[Ffmpeg-devel] [Ffmpeg-devel-old] Re: avi out is buggy

[Wolfram Gloger]

Hi,

> Since the posted commands produce a desynched avi from a file that is 
> said to play correctly in mplayer, one could deduce that the streams in 
> it are not inherently synchronized, but the synchro is maintained by the 
> timestamps themselves; in other words, as Michael wrote, at places there 
> are too many or not enough audio samples. Obviously that cant be done if 
> acodec=copy.

Indeed.

> But if the audio is decoded then re-encoded, then ffmpeg 
> *should* be able to produce well-synchronized raw elementary streams at 
> the intermediate stage (after decoding, before encoding) or else the A/V 
> synch code is buggy.

Yes, and this does in fact work with "-async 1" (or perhaps higher,
"-async 50".  I have used this successfully.

> What it does exactly is not 100% clear from the 
> source, ffmpeg.c does not seem to make up its mind clearly whether 
> timestamps or rate-times-count hold the truth. That is, the intermediate 
> stage itself is not a well-specified format, the input and output 
> formats contaminate it.

I do not see what you mean here -- the "intermediate stage" is raw
data frames (16bit per channel for audio, AFAICS), but for
synchronization purposes _only_ the timestamps hold the truth (also
AFAICS).

Regards,
Wolfram.