[whatwg] Quality Values for Media Source Elements

[Aryeh Gregor]

On Sat, Dec 12, 2009 at 9:32 PM, Hugh Guiney <hugh.guiney at gmail.com> wrote:
> So, in my first foray into preparing Theora/Vorbis content, for use
> with <video>, I realized that I wasn't sure with what settings to
> encode my materials. Should I:
>
> A.) Supply my visitors with the best possible quality at the expense
> of loading/playback speed for people on slower connections
>
> B.) Just account for the lowest common denominator and give everyone a
> low quality encode
>
> or
>
> C.) Go halfway and present a medium quality encode acceptable for
> "most people"?

The usual tactic taken by popular video sites today is to provide
multiple quality levels, serve one by default, and give the user an
option to choose their preferred quality level.  For Flash video, you
might use some kind of Flash script, while for HTML video, you'd use
JavaScript and/or hyperlinks, but the effect is pretty much the same.
HTML video seems to be precisely on par with Flash video in this
regard right now.

> <video controls>
>  <source src='video-hd.ogv' quality='1.0' type='video/ogg;
> codecs="theora, vorbis"'>
>  <source src='video-hq.ogv' quality='0.5' type='video/ogg;
> codecs="theora, vorbis"'>
>  <source src='video-sd.ogv' type='video/ogg; codecs="theora, vorbis"'>
> </video>
>
> . . .
>
> The UA could then have a playback setup that would allow the user to
> specify how it should handle content negotiation for multiple-source
> media. This could be based solely on the quality attribute if
> provided, or if @type is also provided, also based on what
> content-type the user prefers.

I don't think the proposed syntax is useful if you use a
floating-point number with no fixed scale for quality.  Different
sites would use the same number to mean different things, so users
couldn't usefully specify a global preference.  A bitrate or something
would make more sense.

I'm not sure the benefit of permitting quality preferences to be set
across all sites would end up being worth it.  Users are probably
happy enough setting them per site, especially since different sites
might have better or worse video for a given bitrate (or any
artificial quality metric you might think up).  At best, I'd think
this falls into the "don't consider for addition to spec until
browsers have implemented what's already there" category.