[theora] Re: OGM Container?

ChristianHJW christian at matroska.org
Wed Nov 12 12:06:33 PST 2003

Samuel Torres wrote:
> My questions about Ogg and OGM are: Is there a difference other than the 
> name? I understand why Windows oriented people would want different 
> extensions. I also know that the first tools created for making OGM 
> files were based on modifications of the original Ogg source code.  I'm 
> wondering if the actual methods used by OGM creating tools have strayed 
> off what is planed for the official Ogg methods? Will the containers and 
> their standards be identical, compatible, or incompatible?

Tobias Waldvogel, the author of the original OGM tools based on 
DirectShow Ogg muxer, Ogg splitter, Vorbis decoder and Vorbis encoder 
filters created them such that basically every ACM ( Audio Codec Manager 
) and VCM ( Video Codec Manager ) codec can be used, as well as the ( 
very rare ) DirectShow codecs.

To allow that he found a way to copy the according VfW ( Video for 
Windows ) structures for codec identification and stream description, 
namely BITMAPINFOHEADER ( video, VfW ), WAVEFORMATEX ( audio ), as well 
as VIDEOINFOHEADER and VIDEOINFOHEADER2 ( DirectShow ) into the Ogg 
commentary fields, and read them back from there to initalize the 
decoders during playback.

Its up to the Theora devs to comment how this will match with future 
'official' Theora implementations. After all, Tobias was using libogg in 
a very intelligent way, so for sure the streams itself are very Theora 
compatible with respect to how the frames are packed into the Ogg 
container. It maybe would be a wise thing to consider adding this to the 
official specs as a 'VfW compatibility mode', similar to how this is 
handled on another opensource container format to allow support for all 
VCM and ACM codecs.



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