Content Protection @ref and @refID attributes

[haudiobe]

5th edition of DASH and dash.js support @ref and @refID attribute. This should be added to part 6 of v5. Please check with Alex for details.

[lpiron]

There is an existing small paragraph on this in part 6 (copied here for clarity):

"As it can be seen from the above MPD example, the ContentProtection descriptor may be verbose depending on the DRM system. As an MPD may contain several adaptation sets that are accessed with the same DRM data, either in the same period of between periods, in order to reduce the size of the MDP, [3] clause 5.8.4.1.4 defines a mechanism allowing to reference ContentProtection descriptor. The element having the reference shall copy data from the element that is the source as specified in [3] clause 5.8.4.1.3. In addition, referencing shall be done only between ContentProtection elements with the same @schemeIdUri value."

Should it be extended? Adding an example?

[nicoweil]

The first stream (https://d24rwxnt7vw9qb.cloudfront.net/out/v1/feb9354da126479386ae8d47ba103cf8/index.mpd) in the DRM section of dash.js public samples is an example of such ref/refid stream produced by Elemental MediaPackage. It can be used to craft a sample for the spec if needed.