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: [EME] specification question: key Sytem selection

From: Zhouhaojun <zhouhaojun@huawei.com>
Date: Mon, 2 Jul 2012 17:42:04 +0800
To: "'Mark Watson'" <watsonm@netflix.com>
CC: <public-html-media@w3.org>
Message-ID: <004001cd5836$f0e1f1b0$d2a5d510$@com>
Hi Mark,


I think Erics question is that its not clear how UA get to know the key
systems supported by the file.


Here is my understanding: UA can get the information of key systems from the
HTMLSourceElement.keySystem (which is mentioned explicitly in the draft)  or
from the metadata in the file (which is not mentioned in the draft
explicitly, maybe we need some words to explain it).


How UA get initData is not clear too.  See example 7.2.2 other content
decryption module, the app get initData from key needed event before
calling generateKeyRequest. So it seems that UA can get the initData from
the file and set the MediaKeyNeededEvent.initData. Some clarifying words may
be needed also.


Btw, can MediaKeyNeededEvent.keySystem contain multiple supported key
systems, so app can select preferred one from them?



Best Regards,


Haojun Zhou

Email: zhouhaojun@huawei.com

Huawei Nanjing R&D Center, 101 Software Avenue, Yuhuatai District, Nanjing,
Jiangsu, PRC.




: Mark Watson [mailto:watsonm@netflix.com] 
ʱ: 201271 11:43
ռ: Sunyang (Eric)
: public-html-media@w3.org
: Re: [EME] specification question: key Sytem selection


The key system is selected with the call to generateKeyRequest(). If that
keysystem is not supported (by the browser, or by the file) then the call
will fail and the app can try a different keysystem. 


Note that all three of the app, the file and the browser may support
multiple keysystems. Only a keysystem in the intersection of these three
sets may be used. There may still be more than one. The app needs to choose
its favorite from that set, as there may be commercial implications of the
choice for the app. The way we chose to implement that was by allowing the
app to attempt generateKeyRequest with different key systems, in preference
order, until one succeeded. That seems actable given that the set of
keysystems in the intersection I describe above is likely to be very small
(coming up with an example where there are 3, say, is already a challenge).




On Jun 29, 2012, at 8:30 PM, Sunyang (Eric) wrote:

After reading the specification, I have a question on Key System selection.


If media elements source attribute has a keySystem attribute then we use
this as selected keySystem, this is OK.

If no selected KeySystem, the specification says jump to Key Presence


The question is :


At jump to Key Presence is a else if of selected key system, so here
we have no idea about key system,

We may need let app or CDM to analyze the initData to find the KeySystem,
but I have not seen any text for

Analyzing initData here, or I miss something?


So where we select the Key System if no selected key system in media




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Received on Wednesday, 4 July 2012 06:57:41 UTC

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