[MPlayer-users] mpeg2video for DVD authoring?

Fabio Papa f.papa at mcmspa.it
Mon Sep 8 15:34:39 CEST 2003

On Monday 08 September 2003 13:10, Erik Slagter wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > Okay, I haven't gotten around to testing a new stream yet, but I managed
> > to find out the real DVD keyframe requirements.  First I was searching
> > using the word keyframe, which didn't work.. then I searched using
> > i-frame, which didn't work. Finally I realized that what I wanted was
> > to search for "GOP length". It's not that DVDs require a certain rate
> > of i-frames, oh no, its just that there's one I frame per GOP, and
> > there IS a maximum GOP length. grr... Anyway, it turns out this
> > length is 18 for MPEG1 NTSC, 15 for MPEG1 PAL, 36 for MPEG2 NTSC, and
> > 30 for MPEG2 PAL.  If I'm lucky, mplex creates the GOP's accordingly.
> I am afraid mplex can't help you out here. It's the encoder that
> determines the gop size.
> What a strange gop sizes? 30 for MPEG2 PAL means 1 second + 5 frames...

Well, gop lenght determines how much frames the player will skip at once when 
doing fforward or rewind operations. Such values ar not the only correct 
ones, but are in fact the _maximum_ ones. Some sources suggests to use 6 for 
PAL material, which is about a quarter of a sec. The maximum setting is 
supposed to give maximum compression, but it's not noticeable. Furthermore 
some good DVD players, like mine, are able to handle huge gops, even of 250 

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Fabio Papa
Engineering division
Machining Centers Manufacturing S.p.A.
viale F. e G. Celaschi 19 - Vigolzone (PC) Italy

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