[XviD-devel] Re: Aspect Ratio

[Christoph Lampert]

On Thu, 24 Oct 2002, Milan Cutka wrote:

> C> If its easy to do and both dshow filters for XviD, means ffdshow
> C> and xvid filter, support it, there are no incompatibilities either,
> C> maybe only with elder playback filters.
> 
> I'm not sure if this will be so easy to support, because ffdshow (and
> XviD DirectShow filter propably too) needs to know aspect ratio before
> decoding first frame. MPEG2 demuxers provide this information in
> VIDEOINFOHEADER2 structure, but I don't know where this information
> would be stored in AVI - maybe appended to VIDEOINFOHEADER (if that's
> possible).

My point that first of all it's _easy_ to implement the encoding 
stage. It's just 4 bits. 

In my oppinion, the decoder doesn't really have to care about it, unless
it has a buildin rescale-mode. 
But in times of video-overlay, output scaling is most likely done by
hardware in the graphics card, so the decoder would just need an option to
determine the AR information to the player (and the player an option to
read it, of course). 

gruel