Issues with cbcs protected content playback on chrome (fixed)

[ashish157]

Hi All,

As per conversation with @dsilhavy I'm bringing this topic for discussion. So recently we added cbcs protection scheme support for our content and during testing on the browsers we found that on Chrome (installed on Ubuntu 18.04.5 LTS) the playback failed with MEDIA_ERR_DECODE (CHUNK_DEMUXER_ERROR_APPEND_FAILED error with latest dash.js (full error below). To note, this also happened with latest shaka-player. The playback works fine on firefox with both the players.
@dsilhavy hinted that the issue could be related to the content itself. After backtracking it turned out to be an issue with the senc box in media segments. If we add initialization Vector (IV) in senc box the playback fails on chrome. But if we check Common encryption specs. IV is indeed expected and firefox conforms to this:

aligned(8) class SampleEncryptionBox
extends FullBox(‘senc’, version=0, flags)
{
        unsigned int(32) sample_count;
        {
                unsigned int(Per_Sample_IV_Size*8) InitializationVector;
                if (flags & 0x000002)
                {
                        unsigned int(16) subsample_count;
                        {
                                unsigned int(16) BytesOfClearData;
                                unsigned int(32) BytesOfProtectedData;
                        } [ subsample_count ]
                }
        }[ sample_count ]
}

As of now we don't see any issues and playback works fine on chrome and firefox with both dash.js and shaka-player.

Screenshot of full error on chrome:

[vodlogic]

Please can you confirm what the "fix" was for this issue?

The description suggests that removing the IV made it work on Chrome, but Firefox expects the IV according to the CENC spec.
Did Chrome fix the spec mis-alignment?