[MPlayer-users] Re: changing aspect ratio in avi without reencoding

[ChristianHJW]

"Vladimir Mosgalin" <mosgalin at VM10124.spb.edu> schrieb im Newsbeitrag
news:Pine.LNX.4.51.0302161012390.8915 at localhost.localdomain...
> Documentation says that aspect ratio can be stored in mpeg4-inside-avi
> files, but only mplayer will understand it (although I don't think it's
> a problem to add this to windows players, if you mail their authors).
> But that's enough for me.
> Vladimir

Unfortunately its not that easy on Windows, as most players there are
DirectShow based. The problem is ( as Milan Cutka was pointing out ) that
you have to know the output AR before rendering the playback graph.
Unfortunately you can only read the AR flag from the codec header AFTER the
graph is already built, so you are in deep shit.

Milan was recommending to 'abuse' some of AVIs comment tags to store the AR
there. That way the value could be read before the playback graph is
rendered and correct width/height be set on output. MPEG container does have
such a flag and it will be read from MPEG DShow parser before building the
graph, so it works fine for MPEG on DShow, but not for AVI.

Christian
http://matroska.org