[theora-dev] YUV Format
Timothy B. Terriberry
tterribe at vt.edu
Thu Apr 1 05:00:14 PST 2004
> Heres the list i haev to work from... could someone tell me which of
> these it is ?
I have no idea if Microsoft has a specific code for it. The data is
stored in a planar fashion. Video is stored in an 8-bit per channel
Y'CbCr space. See doc/color.html for a precise specification of the
color space used. The current library only uses 4:2:0 decimation
(decimation of the chroma planes by 2 in both the horizontal and
vertical direction). Each component, Y', Cb, and Cr, are in separate
buffers, as suggested by the three separate pointers to them in struct
The horizontal stride in each buffer is always 1. So the contents of a
single row are always contiguous in memory. The vertical stride in each
buffer is NOT the width. So separate rows are NOT contiguous in memory.
The y_stride and uv_stride variables tell you what to add to your
pointer to get to the next row. The fact that there is only one value
for the Cb and Cr planes indicates that each separate Cb and Cr buffer
uses the same memory organization, NOT that they are stored in the same
buffer. You will note that this value is negative in the buffers
returned by the current library, indicating that each row after the top
row actually comes BEFORE the top row in memory. There is no guarantee
that libtheora will always do this.
Note also that libtheora may overwrite the contents of the buffer the
next time you decode a frame. If either DirectShow does not have a way
of describing the buffer layout given above or you need to keep data
around for longer than a single frame decode cycle, you will need to
copy the contents of the buffer somewhere else. You can then use
whatever memory organization suits your fancy.
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