Re: 答复: [EME] specification question: key Sytem selection

On Mon, Jul 2, 2012 at 5:42 PM, Zhouhaojun <zhouhaojun@huawei.com> wrote:

> Hi Mark,****
>
> ** **
>
> I think Eric’s question is that it’s 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).****
>
> **
>

Right, I guess the UA or CDM will analyze the initialization data in meda
data of the media content,  then the UA will know the key system, and fire
in the needKey event, but I have not seen the description.


>  **
>
> 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?
>

I am also wondering about it, so this will save the canPlayBack call to the
UA


> ****
>
> ** **
>
> ** **
>
> Best Regards,****
>
> ** **
>
> Haojun Zhou****
>
> Email: zhouhaojun@huawei.com****
>
> Huawei Nanjing R&D Center, 101 Software Avenue, Yuhuatai District,
> Nanjing, Jiangsu, PRC.****
>
> ** **
>
> ** **
>
> ** **
>
> *发件人:* Mark Watson [mailto:watsonm@netflix.com]
> *发送时间:* 2012年7月1日 11:43
> *收件人:* Sunyang (Eric)
> *抄送:* public-html-media@w3.org
> *主题:* 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).
> ****
>
> ** **
>
> …Mark****
>
> ** **
>
> 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 element’s 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
> element?****
>
>  ****
>
>  ****
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> 华为技术有限公司 Huawei Technologies Co., Ltd.
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-- 
Yang
Huawei