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RE: [EME] Specification Question, do we really need canPlayType("codecs","Key System")?

From: John Simmons <johnsim@microsoft.com>
Date: Tue, 10 Jul 2012 06:45:49 +0000
To: "Sunyang (Eric)" <eric.sun@huawei.com>, "public-html-media@w3.org" <public-html-media@w3.org>
Message-ID: <FF4EB51321FAE847A9650D1E9ABB57A440B3BDA2@TK5EX14MBXC302.redmond.corp.microsoft.com>
The initialization data may not be in the media content. For example, a DASH MPD - live or on-demand - with an initialization segment in the cloud. In addition, there may be more than one CDM available to the UA.

This raises the more general question regarding the scenarios that must be supported by EME.

Where the initialization data resides:

1.  in the media content

2.  in an initialization segment in the cloud

3.  all or in part conveyed with the application (e.g. DASH MPD parsed by the JavaScript which includes ContentProtection elements associated with a Key System)

How many key systems are supported by the media
a. one key system
b. multiple key systems (e.g. common encryption)

How many key systems are on the device support the media
x. none that match the media key system(s)
y. one that matches the media key system(s)
z. multiple that match the media key system(s)

I believe all of these (1-3) x (a-b) x (x-z) = 18 scenarios may occur. And at least some of them require canPlayType() extension. Does this make sense?

John C. Simmons | Media Platform Architect | Microsoft Corporation | direct 425-707-2911  | mobile 425-269-5759

From: Sunyang (Eric) [mailto:eric.sun@huawei.com]
Sent: Monday, July 09, 2012 8:18 PM
To: public-html-media@w3.org
Subject: [EME] Specification Question, do we really need canPlayType("codecs","Key System")?

Does the UA decide Key System based on initialization data of media content?

If the needKey event have not reported Key System to app, it means UA cannot recognize the initData's encrypted mechanism, this may mean that the UA does not support this Key System.

When we touch the UA with canPlayType("codecs" , "key system"), I think we are just trying to find what key systems are supported for certain media formats or containers, but if the UA does not recognize the content's key system, how can it support the key system we embedded in canPlayType.

If we choose a different key system to test the UA, and the UA support, does it mean we need to abort the media resource fetch algorithm and change to a different content format encrypted by supported key system?

So I doubt the real sense of canPlayType extension for key system detection, why not let needKey event report the codesc+key system pairs list to app when the UA cannot recognize the key system from the initialization data? Even if we report this information, the app will change to anther encrypted media source supported by the UA?

Received on Tuesday, 10 July 2012 06:46:43 UTC

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