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

From: <bugzilla@jessica.w3.org>
Date: Tue, 01 Oct 2013 14:45:07 +0000
To: public-html-bugzilla@w3.org
Message-ID: <bug-17673-2486-TKvG316yFh@http.www.w3.org/Bugs/Public/>

--- Comment #30 from johnsim@microsoft.com ---
It has been proposed that section 7.2 - as originally proposed 
(https://www.w3.org/Bugs/Public/show_bug.cgi?id=17673#c4) - 
- only specify initialization data for ISOBMFF Media using the “cenc”
protection scheme. 

This does not address the issue first brought up by David Singer at TPAC 2012 -
that other protection schemes are possible and should be supported. The
proposal at that time was to go beyond concatenated 'pssh' boxes to include the
protection scheme information box 'sinf', which includes the scheme type box
'schm' and the scheme information box 'schi'. Doing this, however, has led to
numerous problems, as documented in this bug - including complexity.

Two proposals: 1) retain the more general formulation in the specification to
allow flexibility for any future protection schemes. 2) as suggested by David
Dorwin, https://www.w3.org/Bugs/Public/show_bug.cgi?id=17673#c14 - avoid trying
to address the general case and include specific instances for each protection
scheme proposed.

I prefer the former, since I am aware of no protection schemes other than
'cenc' that are being proposed to be used with EME, at least in our conference
calls. Providing a general solution as well as the "cenc" specific solution
would address all known issues.

In either case, for "cenc", there would be the simple, concatenated 'pssh' box
formulation of InitData, and a separate ISOBMFF section for the general case.

I would recommend removing any reference to the 'tenc' box in the 'cenc'
section, since as David points out - this information is irrelevant to the
license server - and by design the contents of the 'pssh' box are intended to
convey all information needed for key acquisition.


This does, I believe, address the key rotation issues raised by Steven
Robertson https://www.w3.org/Bugs/Public/show_bug.cgi?id=17673#c10, because key
rotation in practice for "cenc" is conveyed through 'pssh' boxes embedded in
the track fragments.

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