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RE: [media] issue-152: documents for further discussion

From: Bob Lund <B.Lund@CableLabs.com>
Date: Fri, 20 May 2011 09:41:30 -0600
To: David Singer <singer@apple.com>
CC: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>, "Mark Vickers @ Comcast" <mark_vickers@cable.comcast.com>, Eric Winkelman <E.Winkelman@CableLabs.com>, David Agranoff <d.agranoff@CableLabs.com>
Message-ID: <114DAD31379DFA438C0A2E39B3B8AF5D0185B204B3@srvxchg>
Hi Dave,

Would this be in the context of MPEG-2 TS or some other container format? If the MPEG-2 TS case, is the PMT still used to identify the "track" PID?

Thanks,
Bob

> -----Original Message-----
> From: David Singer [mailto:singer@apple.com]
> Sent: Thursday, May 19, 2011 5:29 PM
> To: Bob Lund
> Cc: Silvia Pfeiffer; HTML Accessibility Task Force; Mark Vickers @
> Comcast; Eric Winkelman; David Agranoff
> Subject: Re: [media] issue-152: documents for further discussion
> 
> I may be getting into the middle of something I don't understand, but...
> 
> * we can easily add a metadata tag to MP4 tracks to declare their
> kind/role
> * MP4 has metadata tracks, that could be used to carry any format (it
> just needs defining)
> * we can use caption track events with a caption track that has no
> visible text (we may need a tag for the 'cookie')
> 
> On May 18, 2011, at 8:44 , Bob Lund wrote:
> 
> >
> >
> >> -----Original Message-----
> >> From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
> >> Sent: Tuesday, May 17, 2011 7:36 PM
> >> To: Bob Lund
> >> Cc: HTML Accessibility Task Force; Mark Vickers @ Comcast; Eric
> >> Winkelman; David Agranoff
> >> Subject: Re: [media] issue-152: documents for further discussion
> >>
> >> On Wed, May 18, 2011 at 12:44 AM, Bob Lund <B.Lund@cablelabs.com>
> wrote:
> >>> Hi Silvia,
> >>>
> >>> I had considered @data- attributes but was unsure of the
> >>> implications
> >> of this statement in section 3.2.3.8 of the current HTML5 spec
> >> (http://dev.w3.org/html5/spec/Overview.html#embedding-custom-non-
> >> visible-data-with-the-data-attributes):
> >>>
> >>> "User agents must not derive any implementation behavior from these
> >> attributes or values. Specifications intended for user agents must
> >> not define these attributes to have any meaningful values."
> >>>
> >>> In the case of in-band tracks, the user agent will have to create
> >>> the
> >> DOM equivalent of the @data- attribute for metadata tracks. This
> >> appeared to me as being in conflict with the second sentence of the
> >> above quote. Is this not the case?
> >>
> >>
> >> Where would a UA get the information about the special track type
> >> from from in-band metadata tracks?
> >
> > MPEG-2 transport streams contain program map tables that identify each
> program id with a type, e.g. video, audio, EISS
> (http://www.cablelabs.com/specifications/OC-SP-ETV-AM1.0-I06-
> 110128.pdf)m etc. MPEG-2 TS may be used directly over HTTP or as the
> fragment format in HTTP live streaming and DASH.
> >
> >> Do you know fields in MP4, Ogg and WebM that provide such
> >> information?
> >
> > Fragmented MP4 will be carried in some adaptive bit-rate containers,
> e.g. certain DASH profiles. In this case, the metadata tracks will be
> identified in the manifest file. However, with respect to the HTML5
> "timed text track" API these are still in-band, i.e. not sourced from an
> external file. In this case, there is still the need to identify the
> type of metadata. Discussions are taking place now in MPEG and other
> places regarding requirements for identifying metadata tracks in DASH.
> >
> >> If there is such a field that you need exposed on top of what is
> >> already there, then it would indeed make sense to include that.
> >
> > As described above, there is or will be such a field.
> >
> >> But I honestly doubt that you will find in-band tracks that will tell
> >> you that they contain adinsertion information or syncwebcontent data.
> >
> > See above.
> >
> >> This is all very application-specific
> >
> > You are right these are application specific but in the broadcast
> > industry these applications are common: ETV
> > (http://www.cablelabs.com/advancedadvertising/etv/), ad insertion
> > (http://www.scte.org/documents/pdf/standards/ANSI_SCTE%2035%202007%20D
> > igital%20Program%20Insertion%20Cueing%20Message%20for%20Cable.pdf) and
> > parental control content advisories
> > (http://www.ce.org/Standards/browseByCommittee_2524.asp)
> >
> >> and therefore can only be solved with external text tracks IMHO.
> >
> > Out-of-band timed text tracks work well for file based content but I
> don't think will work for linear streams with no start or end.
> >
> >> Always open to hear a real-world use case though!
> >
> >>
> >> Cheers,
> >> Silvia.
> >
> > Thanks,
> > Bob
> >
> 
> David Singer
> Multimedia and Software Standards, Apple Inc.
Received on Friday, 20 May 2011 15:41:58 GMT

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