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Re: Encrypted Media proposal (was RE: ISSUE-179: av_param - Chairs Solicit Alternate Proposals or Counter-Proposals)

From: Kornel Lesiński <kornel@geekhood.net>
Date: Tue, 28 Feb 2012 00:39:50 -0000
To: "Mark Watson" <watsonm@netflix.com>
Cc: "HTML WG (public-html@w3.org)" <public-html@w3.org>, "Adrian Bateman" <adrianba@microsoft.com>, "David Dorwin" <ddorwin@google.com>
Message-ID: <op.wac5gofste2ec8@aimac.local>
On Mon, 27 Feb 2012 23:27:42 -0000, Mark Watson <watsonm@netflix.com>  
wrote:

>>> We'd like to get people's feedback on the proposal. It is posted here:
>>> http://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media.html
>>
>>
>> In section 5.1. of the proposal there are steps:
>>
>> 2. Detect whether the frame is encrypted.
>> 	 If the frame is encrypted
>> 	 Run the steps above. ([...] Use handler to Decrypt the block [...])
>>
>> 3. Decode the frame.
>>
>> 4. Provide the frame for rendering.
>>
>>
>> Do I understand correctly that once user is authorized CDM gives  
>> browser access to the decrypted bitstream of the media being played?
>
> It's not as clear as it could be, but the intention is that all three of  
> the following are possible, depending on the CDM:
>
> (1) The CDM returns the decrypted frame to the browser
> (2) The CDM handles decryption and decoding and returns the decoded (raw  
> pixels) frame to the browser
> (3) The CDM handles decryption, decoding and rendering and (possibly)  
> returns some kind of reference to the decoded frame to the browser
>
> (3) for example might be what happens on a TV that includes a secure  
> media pipeline as part of the platform. In that case the CDM doesn't  
> itself implement the decrypt/decode/render operations but makes use of  
> platform capabilities to achieve these.

Could this be made explicit in the specification (e.g. by adding necessary  
steps to the playback algorithm)? Currently the section 5.1 is normative  
and in my understanding does not enable CDMs to support cases (2) and (3)  
you've listed.

-- 
regards, Kornel Lesiński
Received on Tuesday, 28 February 2012 00:40:21 UTC

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