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

https://www.w3.org/Bugs/Public/show_bug.cgi?id=17673

--- Comment #18 from johnsim@microsoft.com ---
(In reply to comment #17)
> (In reply to comment #16)
> > As I understand it, the various DRMs include different things in their
> > headers, not just the key id in different format. I'm told their choices of
> > what to include are tightly tied to their design and specifically their use
> > or not of certain IPR.
> 
> EME+PlayReady and EME+Widevine are already out there. What do they *need* to
> include in pssh? Looking at the YouTube EME demo files that have pssh boxes
> for PlayReady and another key system (maybe Widevine, but I'm not sure), all
> the data in the pssh boxes seems redundant to me:
> http://lists.w3.org/Archives/Public/public-html-media/2013May/0025.html
> 
> (Redundant assuming that the CENC layer knows about key ids, CENC fixes the
> key length & the algorithm and the Web app knows its own license server
> URLs.)

The contents of the protection system specific header ('pssh') box are by
design protection system specific. It is true that some of the parameters are
the same between DRMs, but when we envisioned DRM-interoperability, we
determined that standardizing metadata specific to key acquisition was a lot of
negotiations for very little gain, so we focused on DRM-interoperable encoding.
I would argue that the adoption of CENC shows we struck the right balance.

In the case of PlayReady, the information you ask about is publicly documented
at this website: http://www.microsoft.com/playready/documents, In the document
"PlayReady Header Object". 

This is the same information which can be conveyed in a DASH MPD PlayReady
ContentProtection element. Arguably it is better to encode this information in
the MPD so that the media itself is service provider agnostic - and therefore
more interoperable. 

The rules for using this ContentProtection element with PlayReady can be found
at the same website, in the document "DASH Content Protection using Microsoft
PlayReady".

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Received on Thursday, 15 August 2013 20:33:19 UTC