[css-color] colorspace for video

[svgeesus]

https://drafts.csswg.org/css-color/#sRGB

Note that this rule does not apply to videos, since untagged video should be presumed to be in CCIR 601.

Really? Isn’t HD video in Rec.709? Shouldn’t video be consistent with images? Or do implementations really do this differently?

Different issue to #286 because video is typically not explicitly tagged; the colorspace is out of band for broadcast video, and absent for web video.

Presuming untagged video to be CCIR 601 is incorrect for video originating from PAL/SECAM systems, incorrect for HD video, and incorrect for 4k video. It is also probably incorrect for video from SLRs and phones. So CCIR 601 is a poor choice as a default here.

Rec.709 is sufficiently close to sRGB (same primaries, very similar transfer curve) that it may be best to assume sRGB. However, it also depends on what existing implementations do and what colorspace conversions are done by hardware video acceleration in current graphics cards.

[svgeesus]

Closing as the spec now clarifies impact of assorted ITU and SMPTE standards on (untagged, broadcast) video.