On Fri, 14 Mar 2008, Thorsten Jordan wrote:

> What about h264, that choses MBAFF on its own, which format must the YUV
> data have for that codec, always progressive or always interlaced? What
> happens on MBAFF/PAFF?
> Can some of the h264 experts give me a hint here please? thanks

I don't know. But I can only think of 2 possibilities that make sense.
A) Specify chroma subsampling format somewhere in the VUI along with all 
the other colorspace metadata. If that is the case, then it's 
user-specifiable but not specified by default in x264, and independent 
of how any given frame or block is coded.
B) Assume interlaced chroma if any interlace-related features are enabled 
anywhere in the stream, otherwise assume progressive.

Currently I think mplayer uses (B), but (A) is more likely to be the 
standard.

> libx264.c doesn't use the INTERLACED flags mentioned above, so i can't
> tell the encoder what to use...

x264 doesn't *care* what the chroma format is, it just encodes samples. 
The default values x264 puts in the VUI are "unspecified", so if you want 
to specify some metadata for the display to use (assuming the decoder also 
preserves that info, which ffh264 doesn't), then figure out which vui 
element and use that option (which is available in libx264, but not in 
lavc-libx264).

--Loren Merritt
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