[Theora-dev] Problems with Theora DirectShow filters

illiminable ogg at illiminable.com
Wed Sep 15 17:36:21 PDT 2004

----- Original Message ----- 
From: "Timothy B. Terriberry" <tterribe at vt.edu>
To: "illiminable" <ogg at illiminable.com>
Cc: <theora-dev at xiph.org>
Sent: Thursday, September 16, 2004 2:27 AM
Subject: Re: [Theora-dev] Problems with Theora DirectShow filters

> illiminable wrote:
>> Doesn't only one of the input colourspaces to theora work ? I dunno where 
>> i got that impression from... but i thought only the 4:2:0 YUV input 
>> worked at present ?
> I think you are confusing color space with pixel format. When I say "color 
> space", I am talking about the particular primaries, white points, gamma 
> curves, and for Y'CbCr, the mixing coefficients, offsets, extents, etc. 
> Theora defines two different such color spaces, one for PAL content and 
> one for NTSC content. It is expected that the encoder convert content into 
> one of these two spaces, thus minimizing the number of conversion routines 
> needed by a decoder. My understanding was that Windows APIs have no 
> standard way of communicating these parameters to, for example, hardware 
> conversion engines. Most graphics cards these days have some form of 
> YUV->RGB conversion for final display of the output, but what they mean by 
> "YUV" or "RGB" is anybody's guess.

Most of that went over my head ! I'm pretty much just winging it here :-P

I'll go on a google mission !

These are the two references i'm using for YUv/RGB wrt directshow.



> 4:2:0 is just a pixel format. It describes a certain decimation of the 
> chroma components, however those components happen to be defined. It is by 
> itself still an insufficient description, as there are multiple different 
> conventions for where the subsampled chroma values are located spatially. 
> JPEG places them at the average of 4 (for 4:2:0, or 2 for 4:2:2) luma 
> locations, as did MPEG1. MPEG2 only averages in the vertical

Yeah... i've seen this part... the sampling positions of the various DS 
formats are shown on the links above.

I'll have to look a bit more closely !



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