[mythtv] A prelude to transcoding MPEG2->MPEG2

Geoffrey Hausheer ou401cru02 at sneakemail.com
Sat Dec 6 10:38:23 EST 2003

On Sat, 6 Dec 2003 02:40:26 -0500, "Jim Paris jim-at-jtan.com
|mythtv/1.0-Allow|" <elxwhpgqut0t at sneakemail.com> said:
> Yeah, seems like MPEG really just wasn't designed for cutting.
> What we really need is a way to say "here's a frame, decode it to use
> as a reference but don't display it".  Could you pull some trickery
> like giving a bogus PTS to make that happen?

Hard to say, as I still don't really understand how the PTS works.

> Yeah, audio sync could be a pain.  Are you even guaranteed that the
> cut for both audio and video will occur in the same PES?

I dunno.  This is why I'm now considering demuxing/remuxing the audio. 
When I make DVDs using DVD-Lab
 (for Windows), I always need to demux the audio.  I'm not sure why, but
 i think it makes adding chapters easier (you can make sure the PES
 starts at a chapter boundary perhaps?)

> > Considering the complexiity of keeping an MPEG2 stream compliant, I think
> > the easier approach will be the GOPchop approach.
> GOPchop still has issues with audio sometimes, I've heard.  It doesn't
> really handle audio -- it apparently just keeps all non-video data
> along for the ride while doing his chopping and hopes that it works.

Good to know.  Sounds like I should steer clear of GOPchop from what you
and James are saying.

> > However, if anyone knows where I can find a reasonable spec for the MPEG2
> > stream format, I'd be much obliged.  My google searching has turned up
> > lots of useful stuff, but not enough for me to really understand how to
> > begin (for instance I've been able to find zilch on the actual PES and
> > GOP formats.
> I think that there was useful info at http://www.mpucoder.com/dvd/
> (like "MPEG Quick Reference" and "PES headers"), but apparently it's
> no longer freely accessible, so you'll have to make something like a
> $5 donation to get it.  I remember mirroring it once, but I don't
> think I still have it.
> In case you haven't seen it already, there might also be some info
> in this thread:
>     http://www.linuxtv.org/mailinglists/vdr/2003/04-2003/msg00523.html
Thanks for the links.  I sent them my $5.  We'll see what we get (lloks
like a good site tho).  I also found:
which has some good info, though it is in DOC and RAR-compressed.


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