[whatwg] A new attribute for <video> and low-power devices

[Benjamin M. Schwartz]

As I have mentioned earlier, there are some devices that will be unable to
render <video> faithfully inline, due to the limitations of hardware video
accelerators.  However, it occurs to me that there are two essentially
different uses for <video>

1. Important content for the webpage.  An example would be the central
video on a web page whose purpose is to allow users to view that video.
This is currently done principally using Adobe Flash and (to a lesser
extent) <object> tags.

2. Incidental animations.  Examples include decorative elements in a web
page's interface, animated sidebar advertisements, and other small page
elements of this kind.  This was historically a popular use for
animated-GIF, though Flash has largely overtaken it here as well.

In case 1, a browser on a low-powered device may show the video
"full-screen or in an independent resizable window" (to quote the spec).
The browser might also show the video at the specified size, but on top of
the page, rather than at its "correct" location in the middle of the
rendering stack.

However, for case 2, showing the video full-screen or moving it to the top
of the rendering stack would clearly be a bad idea, as the video does not
contain the content of interest to the user.  In this case, if browsers
cannot display the video as specified, they should probably fall back to
the "poster" image.

With the current tag definition, browsers will have to grow ugly
heuristics for this case, based on video's size, aspect ratio, "loop", and
"controls".  To avoid this heuristic hack, I suggest that <video> gain an
additional attribute to indicate which behavior is preferable.  A boolean
attribute like "decorative", "incidental", or "significant" would greatly
assist browsers in determining the correct behavior.

--Ben

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