YUV format in WebM

[Philip Jägenstedt]

We're re-implementing color space converters for the WebM integration in
Opera and can find no authoritative definition of what the color space is.
VP8 does not define a color space beyond "YUV 4:2:0", so presumably it is
left to the container.

Our best guess is that it is ITU-R BT.601 [1] but does that mean that HD
content in ITU-R BT.709 [2] cannot be correctly represented in WebM? Does
any browser support both formats? How about the TH_CS_ITU_REC_470M (NTSC)
and TH_CS_ITU_REC_470BG (PAL/SECAM) color spaces that Theora supports?

[1] http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
[2] http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.709_conversion

--
Philip Jägenstedt
Core Developer
Opera Software

[John Koleszar]

I think today it's defacto 601 only. There's nothing in the container
to indicate otherwise. The VP8 spec is imprecise and refers to a
"601-like" colorspace, which I read to say it's up to the applications
to coordinate. Content in 709 and other colorspaces should be
rematrixed before being encoded to WebM. 601 is what the other browers
are doing AFAIK, but doing a proper survey would probably be a good
idea. It'd be good to be able to say something more concrete than
this.