[Bug 21333] New: consequences of requirement in section 8 on initialisation segments

https://www.w3.org/Bugs/Public/show_bug.cgi?id=21333

            Bug ID: 21333
           Summary: consequences of requirement in section 8 on
                    initialisation segments
    Classification: Unclassified
           Product: HTML WG
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Media Source Extensions
          Assignee: adrianba@microsoft.com
          Reporter: oipfjon@gmail.com
        QA Contact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-media@w3.org

This issue arises from joint discussions between the Open IPTV Forum, HbbTV and
the UK DTG. These organizations originally sent a liaison statement to the W3C
Web & TV IG:

https://lists.w3.org/Archives/Member/member-web-and-tv/2013Jan/0000.html (W3C
member only link)

We have some concerns about the following language in section 8.1.

"The following rules apply to all initialization segments within a byte stream: 
1.    The number and type of tracks must be consistent.
For example, if the first initialization segment has 2 audio tracks and 1 video
track, then all initialization segments that follow it in the byte stream must
describe 2 audio tracks and 1 video track.
....
4. Codecs changes are not allowed.

For example, a byte stream that starts with an initialization segment that
specifies a single AAC track and later contains an initialization segment that
specifies a single AMR-WB track is not allowed. Support for multiple codecs is
handled with multiple SourceBuffer objects."

Firstly we are trying to understand the consequences for our advert insertion
use-cases.

Adverts are unlikely to have the same video and audio tracks as the main
content item and may not have the same codec (particularly audio). Hence these
restrictions would seem to force adverts to be handled as separate SourceBuffer
objects from the main content items.

Is a (relatively) seamless transition between content from different
SourceBuffers possible with MSE?

Secondly all 3 organisations had lengthy and controversial debates last year
about requirements for a common initialisation segment in DASH. It is
understood that MPEG are defining new boxes to enable new initialisation data
to be carried in-band. This language would seem to exclude the use of those new
boxes and again would force the use of separate SourceBuffers. Is this correct?

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Received on Tuesday, 19 March 2013 12:44:54 UTC