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

[Sébastien Mazy]

On Tue, Aug 5, 2008 at 11:41 PM, The Wanderer
<inverseparadox at comcast.net> wrote:
> 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.

Thanks for the clarification.

> 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.

A positive value, delays the video as stated in the man page. The
sound stills plays immediately.

> 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.

Sorry this "blank audio" vocabulary was confusing. There is no audio
during the 14 first seconds of the file indeed. I can confirm that
with VLC for example (I can hear my sound card coming out of
auto-suspend power mode after 14s of playing, which shows that VLC
does not send sound to the sound card before that time).

> 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?

The demuxed audio doesn't contain any blank sound, which confirms what
you said. I'm pretty sure prepending blank sound will solve the
problem but it will not be the same video then.

>> 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...

Let me put an example:
1) you let mplayer play the file without interfering from the begining until 20s
2) you start playing at 20s directly (by seeking with a keyboard
shortcut or the -ss option)
In both cases you are at the same time of the video (20s), but you do
not hear the same sound. 1) is 14 sec earlier than 2). That's not
consistent.

>> 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.)

http://dl.free.fr/pPpCUreUq should be accessible by anyone.


Since other players such as VLC/Xine/Totem can handle this file, I
think there are two possibilities:
- either it is "standard" (provided avi is a standard) to have a sound
track in an avi file which starts at any time and mplayer doesn't
handle this (-> bug)
- or it isn't, a sound track should always start at 0s in an avi file
and the other players are to blame for being too tolerant with a non
standard avi file ().


Cheers,
-- 
Sébastien Mazy