[whatwg] Serving up Theora <video> in the real world

[Philip Jagenstedt]

On Fri, 10 Jul 2009 19:23:44 +0200, Aryeh Gregor
<Simetrical+w3c at gmail.com> wrote:

> On Fri, Jul 10, 2009 at 4:57 AM, Robert O'Callahan<robert at ocallahan.org>  
> wrote:
>> The way we've implemented in Firefox, we'll return "yes" if you specify  
>> a
>> codecs parameter and we support every codec in your list. So
>> v.canPlayType("video/ogg; codecs=vorbis,theora") returns "probably" in
>> Firefox 3.5. I think this is reasonable because I believe that, modulo  
>> bugs
>> in our implementation, we support the full Theora and Vorbis specs. On  
>> the
>> other hand, we will return "maybe" for v.canPlayType("video/ogg"). I  
>> think
>> this distinction will be useful.
>
> In what use-case would an author want to make use of the distinction?
> In either case, your only course of action is to try playing the
> video.  Maybe you'd try testing all the video types you support, and
> if one is "maybe" while another is "probably" you'd go with
> "probably"?  That seems like a pretty marginal use case to help for
> the sake of such a confusing API.  Programmers expect binary logic,
> not ternary (look at the complaints about SQL's NULL).

I agree that the current interface is ugly and quite fail to see what the
use for it is. With a boolean return value, canPlayType("application/ogg")
would return true if one can demux Ogg streams.
canPlayType("application/ogg; codecs=vorbis,dirac") would return true if
one can demux Ogg and decode vorbis + dirac. Differentiating between
"maybe"/"probably" really seems like an edge use case, but you could if
you really wanted to:

function tertiaryCanPlayType(mime) {
     [container, codecs] = mime.split(";");
     if (canPlayType(mime)) {
       return codecs ? "probably" : "maybe";
     } else {
       // if there are codecs, canPlayType(container) would tell you if
problem is with the container format or the codecs
       return ""; // was "no"
     }
}

Unless there's some compelling use case that can't be handled with the
above I'd support canPlayType returning a boolean. The only issue I can
see is that canPlayType(foo)==true might be interpreted as a strong
promise of playability which can't be given. In that case just rename the
function to wouldTryTypeInResourceSelection (no, not really).

-- 
Philip Jägenstedt
Core Developer
Opera Software