Do not include PSSH boxes into media files by default, if they will be included into manifests as well

[vladimir-kazakov]

By default, when creating protected DASH content, Shaka Packager adds PSSH boxes both into media and manifest files. This can be reproduced using the following command:

packager \
  'in=In/aac-lc-128k.m4a,stream=audio,output=Out/aac-lc-128k.mp4' \
  'in=In/h264-360p-750k.mp4,stream=video,output=Out/h264-360p-750k.mp4' \
  --protection_scheme cbcs --clear_lead 0 \
  --enable_raw_key_encryption --protection_systems Widevine \
  --keys 'label=:key_id=11111111111111111111111111111111:key=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA' \
  --segment_duration 2 --fragment_duration 2 \
  --mpd_output Out/dash.mpd

Both DASH-IF IOP (4.3; the latest currently) and CMAF (1st edition; the latest currently) recommend to include PSSH boxes only into manifests.

For example, DASH-IF IOP, in the section 7.7.1, says:

'pssh' boxes SHOULD NOT be present in Initialization Segments

There is also an explanation why it's a bad idea to include PSSH boxes into media files. Other sub-sections of the section 7 may also provide additional information.

Another example - CMAF, in section 7.4.3, says:

CMAF streaming applications should signal license acquisition information in the manifest and should not duplicate the information in this box in CMAF headers.

The section 8 provides more info about this recommendation.

Of course, there is an option to explicitly tell to the packager to not include PSSH boxes into media files:

--mp4_include_pssh_in_stream=false

It works as expected, but the problem is that by default the packager tries to be compatible with DASH-IF IOP, which does not recommend such behavior. The packager does it, because of the following option:

--generate_dash_if_iop_compliant_mpd

Which by default is set to true.

So, if generate_dash_if_iop_compliant_mpd is set to true, the mp4_include_pssh_in_stream must be implicitly set to false. In other words, DASH-IF IOP and CMAF compliant content must not contain PSSH boxes in media files, if these PSSH boxes will be added to manifests.

I'm using Shaka Packager c257113-release on Ubuntu 18.04.3 inside a Docker container (google/shaka-packager, b5ec0eef40bc).

[kqyang]

@vladimir-kazakov Thanks for the reminder. We do plan to enable the flag 'mp4_include_pssh_in_stream' by default at some time. I'll add it to the next milestone so we don't forget about it.

[kqyang]

Move it to v2.5 milestone, but will do it in v2.4.1 minor release.