[whatwg] Video source selection based on quality (was: <video> feedback)

[Gregory Maxwell]

On Tue, Feb 16, 2010 at 10:33 AM, Tim Hutt <tdhutt at gmail.com> wrote:
[snip]
> It's up the UA. It can ping the server if it wants. If I were writing
> the UI for firefox, for example I would have it do the following:
[snip]
> 3. If the default isn't the highest quality, show a little "Better
> quality available" tooltip similar to youtube's "Watch in HD".
> 4. If the video stutters a lot, and there is a lower quality video
> available, display a (non-modal) message along the lines of "Lower
> quality video is available, it may work better."


Imagine that you are a user-agent. Place these streams in order of "quality":

1.  854x480 4:2:0 @  1mbit/sec. average rate.
2. 1280x720 4:2:0 @  1mbit/sec. average rate.
3.  640x360 4:4:4 @  2mbit/sec. average rate.

Or these:

1. 640x360 4:2:0 @   1mbit/sec. average rate peaking to 1.4mbit/sec
(over 64 frames).
2. 640x360 4:2:0 @ 0.7mbit/sec. average rate peaking to 8mbit/sec
(over 64 frames).

Or:

1. 640x360 "simple profile" @ 800kbit/sec average
2. 640x360 "super-ultra mega profile requiring a water-cooled
supercomputer to decode" @ 700kbit/sec average.


I don't think it's hard to imagine that in each of these cases there
exists a real "quality" ranking which the creator of the videos could
be well aware of, but that no user-agent could determine
automatically.

Moreover, even the "switch to a lower rate if you are exhausting your
buffer" isn't a necessary a good strategy when the 'lower rate' stream
is one which places more buffer pressure.