[MPlayer-users] Significant audio delay on an avi file with blank audio

[The Wanderer]

Sébastien Mazy wrote:

> Thanks for your answer!
> 
> On Tue, Aug 5, 2008 at 10:04 PM, The Wanderer
> <inverseparadox at comcast.net> wrote:
> 
>> Have you tested what happens with the -delay option?
> 
> mplayer -delay -14 blank_audio_delay.avi
> 
> resulted in:
> - image lag during a few seconds + "Your system is too SLOW to play
> this!" message on stdout (which is not the case, my CPU is enough for
> a low-def divx)

Yeah - the "system too slow" message just means that the A and V values
have gotten out of sync by more than a certain minimum, which in this
case is roughly what we're asking for.

> - the sound starting immediately, the video starting at 14s (though a
> negative value for -delay is supposed to delay the sound according
> to the man)

The sign of delay is a little hard to keep track of, and I've seen it be
inconsistent between the different methods in the past. Try with a
non-negative value as well and see if that changes anything.

>> What happens if you start playing with the -ss option and then try
>> to seek back to before the sound began? Does it get out of sync,
>> play video without audio (and remain in sync), or refuse to seek
>> back that far?
> 
> It goes out of sync, just as if I had started playing the file from
> the beginning. Mplayer skips the blank audio whenever you start
> playing before the assumed start of the sound at 14 seconds.

My guess would be that there is, in fact, not "blank audio" in the file
for those 14 seconds; my guess would be that there is *no* audio in the
file for that period. If you demux the audio (using e.g. mplayer -ao
pcm), prepend 14 seconds of silence (this can be created with e.g. sox
and prepended with e.g. cat), and remux, does the problem go away?

> Mplayer is not consistent with seeking with this video. If you seek
> before 14s (the approximate start of the non blank audio), the sound
> will always be 14s too early. If you seek after 14s, it will always
> be synchronized.

That sounds consistent to me...

> It seems one can upload files on ftp://upload.mplayerhq.hu/ but not
> download them after.

Yes, that's intentional; to download, you need a non-anonymous account
there, which the developers have. (I don't, although I used to.)

-- 
       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.