[encrypted-media] "cenc" Initialization Data Format: 'pssh' box selection

tinskip has just created a new issue for https://github.com/w3c/encrypted-media:

== "cenc" Initialization Data Format: 'pssh' box selection ==
Section 1 of the "cenc" [Initialization Data Format specification](https://www.w3.org/TR/eme-initdata-cenc/) states that:
"The format is one or more concatenated Protection System Specific Header ('pssh') boxes [CENC], each for a unique SystemID. One of the concatenated 'pssh' boxes should use the Common SystemID and PSSH Box Format."

Would it not be simpler for the application to just grab all the PSSH boxes and concatenate them into init_data without looking at their contents? What if there is more than one box for  a specific system ID?  If there are multiple PSSH boxes with the same SystemID, how should the application pick one? It would seem that this requirement adds complexity without value.

There are conditions under which multiple PSSH boxes for the same DRM system may be appropriate, such as when having different versions which are understood by different versions of a CDM, and which may be arbitrarily large.  The CDM would select the one for a specific version or feature set, and use it when requesting a license.  The only other way to do this would be having multiple system IDs for the same DRM system, which is not desirable.


Please view or discuss this issue at https://github.com/w3c/encrypted-media/issues/440 using your GitHub account

Received on Monday, 16 April 2018 18:06:53 UTC