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

> 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


Makes sense?


-- Pierre

On Wed, Apr 9, 2014 at 2:22 PM, David Singer <> 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 <> 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 <> 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
>>> <> 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:
>>>> 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
>>>>> <> 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
>>>>> <> 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
>>>>> <>
>>>>> 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
>>>> @cconcolato
> David Singer
> Manager, Software Standards, Apple Inc.

Received on Wednesday, 9 April 2014 21:28:25 UTC