Not updating init-data for In-band key rotation signalling is inefficient/wasteful

[prasadkhambete]

https://dashif.org/docs/IOP-Guidelines/DASH-IF-IOP-Part6-v5.0.0.pdf Section 9.3 does not mention that init-data needs to be updated at each key-rotation. Some content packaging providers interpret this to mean that they do not need to update the init-data for each key-rotation.

As per section 9.3 - "The initialisation segment has one PSSH box per DRM allowing to access content and a default_KID value
in the tenc box" - this means that a) content packager cannot omit the PSSH in the moov and default_KID in tenc and b) that it is for "allowing to access content" which means it always needs to fetch a valid license.

If the content packaging providers do not update the init-data, it will have a PSSH for a key that has long since rotated. One particular packaging provider is adding PSSH to every moof, and their expectation was that since the default_KID/PSSH in moof overrides the one in the init-data/moov, the stream should play fine.

For the players/parsers - they have no way of knowing after downloading the init-data that they can or should ignore the PSSH in the init-data. Players will send out the license request as soon as they see the PSSH. A player cannot distinguish easily if the key resulting from the PSSH in the init-data may still be required (for example it may be required to decrypt content until the first in-band key rotation) or not (when the init-data is not updated by the packaging provider). Due to this, it will always issue a license request.

If packaging providers do not update the init-data for each key-rotation this will result in a request for a license that will never be used (which is inefficent and wasteful) and there is also burden on the license provider to provide a valid license response for a key that has already been rotated and no longer active, otherwise playback might fail.

DASH-IOP spec should provide some clarifications that the init-data needs to be updated at key-rotation, and that the same PSSH could be added to the moof segments that follow (until the next key rotation)