Re: [csswg-drafts] Adding of video-* properties and dynamic-range to handle bi-plane scenarios (#4678)

Hi @gregwhitworth, I'm sorry for being so far behind. I do have some feedback, which I'll put it here first, but depending on responses it'll make its way into separate issues / PRs.

## procedural / editorial 
* This PR was made against mq4, but the original issue was tagged against mq5, and I do think it would be a better fit there. Also, MQ4 is in CR already, so effectively under a (soft) feature freeze.
* I'd make all the `video-*` media features be subsections of `6.7. Video Prefixed Features` (turn them from `<h3>`s into `<h4>`s): they're not full fledged sections, but just saying "video-foo is the same as foo, in except in this different context" with some clarifications, so I don't think they should have the same importance in the table of contents.

## Substantive
* For section `6.6 Determining contrast and brightness of display`, I'd do it a little differently. I think non-normative isn't exactly what we're shooting for, and "UA defined" would be a better phrasing. Also, while I agree it should be up to the UA rather than tightly defined by the spec, it still needs some degree of guidance about what the intent is. We are talking about the screens that have the ability to do "brighter than white" highlights and the like, as typically found in video, rather than screens which have a "normal" top brightness and particularly deep blacks, which could also reasonably be described as being high contrast, but aren't what we're interested in here. While leaving the specifics UA defined, there should be some text to express the intent of that definition.

* The definition of `video-width` (same thing for `video-height`) includes this:
    > For continuous media, this is the width of the viewport (as described by CSS2, section 9.1.1 [[!CSS21]]) including the size of a rendered scroll bar (if any). For paged media, this is the width of the page box (as described by CSS2, section 13.2 [[!CSS21]]).

  That text comes from the definition of `width`, but I don't think it is relevant here: I don't think there currently exists such a thing as a paginated media with a dedicated video plane (or a paginated video plane being itself paginated).
  On the other hand, we should add a mention that this is about the size of the entire video plane, not the layout-dependent portion of it that is being clipped and composited with the rest of the page.

* The definition of `video-width` (same thing for video-height) include this:
    > lengths are interpreted according to [[#units]].
 
   I suspect that means we're doing things like measuring in CSS px, not in device pixels. If so, we should be very explicit about this, as this may be counter-intuitive for video. Also, maybe we should consider actually reporting physical pixels here when there is that separate video plane (and if so, also returning 1 as the video-resolution).


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Depending on the responses to the points above, I might file issues / PRs differently, but for now, I expect I'll probably directly commit on the master branch for the first 2 points, propose PRs for the next 2, and to open a new issue for the last one.

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Received on Wednesday, 8 April 2020 03:01:37 UTC