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

From: David Singer <singer@apple.com>
Date: Fri, 20 May 2011 16:36:04 -0700
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: <1BA48D7D-D634-4842-B65C-F917A561B50C@apple.com>
To: Bob Lund <B.Lund@CableLabs.com>

On May 20, 2011, at 8:41 , Bob Lund wrote:

> 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?

I'd have to do some study of the right/best place to put this in m2ts, I'm afraid.

> 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 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.

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Friday, 20 May 2011 23:36:32 UTC

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