[VCDImager Bugs/Devel] Re: SVCD out of sync

[Udo Wolter]

Andrew Stevens wrote:

>> I'm using DV material and conbvert it with the mjpegtools to
>> MPEG2 (SVCD format). After getting the mpg-files I'm using vcdimager
>> & cdrdao to burn them. Under Linux it's absolutely no problem, mplayer
>> can read and play them correctly, no matter if you
>> play the files directly or as track from the SVCD.
>
> How odd...   is the time offset constant or does it grow/decrease with
> playing time?  Do you get the same problems if you encode from some

No. It's constant, maybe between 1/10 to 3/30 seconds.

> other source than DV? If it stays constant you can neatly correct for it 
> using mplex'

I don't have any other source at this time. Anyway, the DV streams look
fine and even the converted mpegs are fine.

> sync offset (the -O flag). If you mux with -O 100 all the video frames will
> have their presentation (playback) timestamps set 100mSec
> later relative to audio and so play back 1/10 second later.

When I'm doing this, I cannot play them correctly with a soft mpeg player
(with linux). So, this is no option for me. The stream should play
perfectly in as many devices as I can use.

>> Or is it vcdimager, cdrdao or even the mjpegtools ?
> -----------------------^
> No chance of the mjpegtools being wrong. They're well known for
> being absolutely *perfect* *bug-free* and *wonderful* ;-) ;-) :-)

:-) Indeed, they're a little slow in MPEG encoding (best quality mode on
an Athlon 1200: 2-3 frames/second), but the output is perfect.
I think it's one of the best free software. Although I have some
problems to compile lav2yuv with DV support (really hard). The
rest is easier.

> Actually, if its not just something in the way DV is being handled I'd

No, I think the DV part is ok. I can play it with several players
and had no problems.

> bet on an mjpegtools problem.   There's really very little cdrdao or
> vcdimager can to affect the relative sync of audio and video (that's

Ok, if you're sure it can't be cdrdao & vcdimager, it can only
be mplex (or maybe mpeg2enc).

> set by the original data-streams fed to mpeg2enc and mp2enc,
> and then modified by mplex).

Today I'll try the new version (1.5.0) from the CVS tree.

>> mplex to 2336 ? Is it better to write 2336 size blocks with
>> vcdimager ?
>
>Roughly: the sector size mplex worries about is *payload* the size vcdimager
>adds some extra info to this when building the image to burn.  2324 is the
>right blocksize.

Ok, Arnd Bergmann told almost the same. I'll believe you two. :-)

>> Another thing is the number of buffers in mplex. In the manual it
>> says it's important for playback. What are they for ?
>
> If you've set standard SVCD output the buffer size assumed by
> mplex will be correct.

No, the old mplex only had upto standard SVCD. I've seen in the new
one the user-rate SVCD. But not tested yet.

> If you're using "user-rate" SVCD then:
>
> 1) You need to specify the buffer size you're assuming for the player
> (anything over 230KB is definately over the specification).

How big is a buffer ? 1 KB ?

> The size number is simply the size mplex *assumes* the decoder playing
> the stream has.  More allows for more efficient handling of temporary bursts
> of activitiy in the video.   Too much means the player can't play it at all!

I've never had this problem, although I pushed the buffers to 300 (whatever
this means in KB).

> If in doubt: 224KB.  N.b. you need to tell mpeg2enc this parameter too
> otherwise it can produce a stream mplex can't *fit* to the assumed buffer
> size.

In mpeg2enc I'm using normally 100 buffers. Is this ok ?
Should buffers-mpeg2enc = buffers-mplex ?

>2) There's no guarantee the SVCD will be playable by every player!

No, but if it's possible to play it in mine (and it does) I'd like to have
it in sync mode. :-)
I hope I'll make it sometime...

Thanx for all your hints, I think I can see some progress here. Although
this forum is not the right place to discuss the mjpegtools, it's a
little bit OT. Anyway, in a way it all belongs together, I can't use
vcdimager without the mjpegtools, maybe other people use other
software. But I don't even know about other (linux) software
doing this...

Bye,
        Udo
-- 
Udo Wolter
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