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[whatwg] Scripted <video> query proposal

From: Eric Carlson <eric.carlson@apple.com>
Date: Fri, 22 Aug 2008 16:21:05 -0700
Message-ID: <6B79BF34-2C34-4437-BB34-915B0F3CF882@apple.com>

On Aug 22, 2008, at 2:36 PM, Robert O'Callahan wrote:

> On Sat, Aug 23, 2008 at 1:46 AM, Eric Carlson  
> <eric.carlson at apple.com> wrote:
>
> On Aug 21, 2008, at 8:56 PM, Robert O'Callahan wrote:
>
>> Does that actually enumerate all supported codecs? Looking at the  
>> Webkit code and the Quicktime docs, it looks like it's just  
>> enumerating file/container types.
>>
>
>   Indeed the code enumerates movie importers and just builds a list  
> of the MIME types supported by QuickTime, so it can not yet deal  
> with a type string with an RFC4281 "codecs" parameter. We are  
> working on that requirement, but the current approach is still  
> useful because the "codecs" parameter is not yet widely used.
>
> That will require extensions to Quicktime, right?
>
   Correct.

> So using your current approach implement Tim's proposed API, we can  
> use this to answer "yes" or "no" if the MIME type contains no codec  
> string, and if the MIME type does contain a codec string we can  
> either answer "no" (if the container is not supported) or "maybe".
>
> I suppose if Tim's willing to assume that anything supporting the  
> Ogg container supports Theora and Vorbis, that's good enough for  
> now ... for Quicktime. We'll have to look into whether something  
> similar is possible with GStreamer and DirectShow. But I guess even  
> if it isn't, a 3-value version of Tim's proposed API is better than  
> nothing.
>
   A three state return is an interesting idea, but wouldn't you then  
be required to return "maybe" for MIME types that can describe  
multiple formats? For example, "video/mpeg" can be used to describe a  
video elementary stream, an MPEG-1 system stream, an MPEG-2 program  
stream, or an MPEG-2 transport stream. "application/ogg" can include  
dirac, flac, theora, vorbis, speex, midi, cmml, png, mng, jng, celt,  
pcm, kate, and/or yuv4mpeg. And then there is "video/quicktime"...

   I think it makes more sense to leave it as a boolean, where "no"  
means the UA does not support the type, and "yes" means that the UA  
implements some support for the type but errors can occur during  
loading and/or decoding.

eric
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