[Bug 17673] Define Initialization Data for implementations that choose to support the ISO Base Media File Format

https://www.w3.org/Bugs/Public/show_bug.cgi?id=17673

--- Comment #38 from Adrian Bateman [MSFT] <adrianba@microsoft.com> ---
(In reply to David Dorwin from comment #37)
> In http://lists.w3.org/Archives/Public/public-html-media/2014Jan/0037.html,
> I suggested that we might use a simple identifier that is *not* a MIME type
> (e.g. "video/mp4") to identify the format of the initData parameter and
> attribute.
> 
> *If* we used an identifier that is *not* a MIME type, we could specifically
> identify the protection scheme in ISO BMFF (i.e. "cenc") and avoid the
> ambiguity or generic solution that has been discussed in this bug.

We've discussed this at Microsoft and we agree that it would be beneficial to
identify the format of the initdata with a string other than the simple MIME
type and doing so would simplify both the spec and implementations by allowing
for "CENC" to be supported without having to handle generic BMFF data even if
the engine will never support anything but CENC content.

> If we did this, we may need some way to detect what format(s) are supported
> since isTypeSupported() currently takes a MIME type. However, we already
> have this issues with ISO BMFF - applications can query whether "video/mp4"
> is supported, but that does not indicate whether "cenc" or some other
> protection scheme is supported.

Separately we agree that isTypeSupported doesn't sufficiently indicate
potential playback support of content. There are a number of arguments to this
determination including key system, container, encryption scheme (e.g. CENC),
encoding format, and probably others. For example, a media engine may support a
particular key system and it may support a particular container but it might
not have a binding for the key system to a particular encoding.

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Received on Tuesday, 28 January 2014 06:38:09 UTC