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Re: [DASH] [MSE] Summary of "Resolving Bug 24370" thread and proposed next steps

From: Pierre-Anthony Lemieux <pal@sandflow.com>
Date: Wed, 9 Apr 2014 14:46:32 -0700
Message-ID: <CAF_7JxBWJv1KgrFRBnewEVBstOrmRDfnpOjwMNKkq8JeutWGkQ@mail.gmail.com>
To: David Singer <singer@apple.com>
Cc: Mark Watson <watsonm@netflix.com>, Cyril Concolato <cyril.concolato@telecom-paristech.fr>, "public-html-media@w3.org" <public-html-media@w3.org>, "dash@lists.uni-klu.ac.at" <dash@lists.uni-klu.ac.at>
Hi David,

> Um, no, IF it is in the file, it's in the kind user-data box in the track.

It might be in a manifest, outside of the ISO BMFF file.

Thanks,

-- Pierre

On Wed, Apr 9, 2014 at 2:31 PM, David Singer <singer@apple.com> wrote:
>
> On Apr 9, 2014, at 23:27 , Pierre-Anthony Lemieux <pal@sandflow.com> wrote:
>
>>> it can really help to have self-describing content.
>>
>> Yes. The "self-description" might not always be in the box specified
>> at [1], and the suggestion is that MSE should support alternative
>> means.
>>
>> [1] http://lists.w3.org/Archives/Public/public-html-media/2014Apr/0055.html
>>
>> Makes sense?
>>
>
> Um, no, IF it is in the file, it's in the kind user-data box in the track.  It doesn't help to be vague, does it?
>
>> Thanks,
>>
>> -- Pierre
>>
>> On Wed, Apr 9, 2014 at 2:22 PM, David Singer <singer@apple.com> wrote:
>>> all agreed, but in a pipeline workflow, where the content creator is not the HTML author (not unlikely) it can really help to have self-describing content.
>>>
>>>
>>> On Apr 9, 2014, at 21:22 , Pierre-Anthony Lemieux <pal@sandflow.com> wrote:
>>>
>>>>> I've no objection to specifying a way to add them into the file, but not all files will have this,
>>>>> so it remains useful to be able to specify these programmatically.
>>>>
>>>> Right. It seems pretty limiting to assume that all ISOBMFF files will
>>>> have the proposed box. In particular, some content might already have
>>>> the information outside the ISOBMFF file, e.g. in a manifest, and/or
>>>> in existing boxes.
>>>>
>>>> Based on the short discussion this morning, it sounds like an
>>>> immediate question is how to tie a 'kind' value with a specific track
>>>> at init, before a TextTrack object is created. Did I get this right?
>>>>
>>>> Best,
>>>>
>>>> -- Pierre
>>>>
>>>> On Wed, Apr 9, 2014 at 10:44 AM, Mark Watson <watsonm@netflix.com> wrote:
>>>>> My comment on this at the meeting was that the track kinds need to be
>>>>> available to the application before any media is downloaded so that the
>>>>> application can decide what media to download. So, they will be in the
>>>>> manifest.
>>>>>
>>>>> I've no objection to specifying a way to add them into the file, but not all
>>>>> files will have this, so it remains useful to be able to specify these
>>>>> programmatically. However, once specified for a track it does not need to be
>>>>> possible to change the kind.
>>>>>
>>>>> ...Mark
>>>>>
>>>>>
>>>>> On Wed, Apr 9, 2014 at 5:56 PM, Cyril Concolato
>>>>> <cyril.concolato@telecom-paristech.fr> wrote:
>>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> As a data point for this discussion, Bob Lund and I submitted a
>>>>>> contribution to the MPEG meeting, held last week in Valencia, to highlight
>>>>>> the problem in the mapping of DASH Role to HTML5 kind. The contribution is
>>>>>> available here:
>>>>>> http://biblio.telecom-paristech.fr/cgi-bin/download.cgi?id=14553
>>>>>> The MPEG group agreed to define 3 new role values ("description", "sign"
>>>>>> and "metadata") as part of the amendment 2 of DASH.
>>>>>>
>>>>>> Cyril
>>>>>>
>>>>>> Le 07/04/2014 09:05, Aaron Colwell a écrit :
>>>>>>>
>>>>>>> In the interest of trying to move forward on the MSE bug 24370, I'm going
>>>>>>> to try to provide a high level summary of the "Resolving Bug  24370" thread
>>>>>>> and propose a way forward. Please forgive me if I accidentally misrepresent
>>>>>>> something.
>>>>>>>
>>>>>>> *Summary:*
>>>>>>>
>>>>>>> 1. Changes in languages are allowed during the course of a presentation,
>>>>>>> but there is some debate about how these should be represented in HTML5. The
>>>>>>> majority opinion in the thread appears to prefer immutable language & kind
>>>>>>> attributes and track objects being added & removed to reflect language
>>>>>>> changes.
>>>>>>>
>>>>>>> 2. Currently track kind can't be signalled in ISO-BMFF content. A new
>>>>>>> box/atom needs to be defined
>>>>>>> <http://lists.w3.org/Archives/Public/public-html-media/2014Apr/0018.html> to
>>>>>>> signal this information.
>>>>>>>
>>>>>>> 3. No argument or example has been given that requires Javascript to
>>>>>>> explicitly change the language or kind of a track. My interpretation of Jim
>>>>>>> Ley's comment
>>>>>>> <http://lists.w3.org/Archives/Public/public-html-media/2014Apr/0015.html> is
>>>>>>> that the application only wants to be notified of changes in the media and
>>>>>>> does not need to be able to change the values on the tracks.
>>>>>>>
>>>>>>> 4. Bob Lund and David Singer appear to explicitly support removing the
>>>>>>> mutable attribute definitions. I believe Silvia Pfeiffer implicitly supports
>>>>>>> their removal based on the arguments she has made in the thread. I also
>>>>>>> support removal of the mutable attribute definitions.
>>>>>>>
>>>>>>> *Proposed Next Steps:*
>>>>>>>
>>>>>>> 1. Remove the mutable attribute definitions for language and kind. I'm
>>>>>>> unclear about the process around this sort of change since this is not an
>>>>>>> "at risk" feature. I'd hate to have to go through a long Last Call process
>>>>>>> again for this.
>>>>>>>
>>>>>>> 2. Work with David Singer and other MPEG savy folks to define a new
>>>>>>> box/atom for ISO-BMFF to carry track kind information. This definition could
>>>>>>> initially live in the ISO-BMFF byte stream format spec
>>>>>>> <https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/isobmff-byte-stream-format.html>
>>>>>>> while it is waiting to be officially standardized by MPEG.
>>>>>>>
>>>>>>>
>>>>>>> 3. Sylvia and/or Hixie update the HTML specs to reflect the expected
>>>>>>> behavior for language & kind changes. I don't have concrete proposals for
>>>>>>> this at the moment, but it seems like there has been confusion around the
>>>>>>> intended behavior when track changes occur mid-playback and whether or not
>>>>>>> the track attributes can change value during playback.
>>>>>>>
>>>>>>>
>>>>>>> *Please indicate your support or opposition to the summary and proposed
>>>>>>> next steps.*
>>>>>>>
>>>>>>> Thank you,
>>>>>>> Aaron
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Cyril Concolato
>>>>>> Multimedia Group / Telecom ParisTech
>>>>>> http://concolato.wp.mines-telecom.fr/
>>>>>> @cconcolato
>>>>>
>>>>>
>>>>
>>>
>>> David Singer
>>> Manager, Software Standards, Apple Inc.
>>>
>>
>
> David Singer
> Manager, Software Standards, Apple Inc.
>
Received on Wednesday, 9 April 2014 21:47:21 UTC

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