Re: Sourcing language information for media tracks

Well, as long as that is what the editors want :) It also makes for a nicer
URL.

On Fri, Mar 11, 2016 at 6:28 PM, Yosuke Funahashi <yosuke@w3.org> wrote:

> I can set up a Github repo for this spec under the W3C account If you
> prefer.
>
> Yosuke
>
> On 3/11/16 5:53 PM, Philip Jägenstedt wrote:
>
>> Silvia, any chance of maintaining this spec on GitHub so that you can
>> accept
>> PRs? Not that I'm volunteering, of course, but this seems like the kind
>> of thing
>> where it'd be appropriate :)
>>
>> On Fri, Mar 11, 2016 at 8:26 AM, Sergey Volk <servolk@chromium.org
>> <mailto:servolk@chromium.org>> wrote:
>>
>>     Hi,
>>     I've been working on adding media track support in Chromium and was
>>     trying to use  the spec at
>>     https://dev.w3.org/html5/html-sourcing-inband-tracks/ for reading
>>     various media track properties.
>>     I've ran into a few issues (see the discussion at
>>     https://codereview.chromium.org/1735003004/ for details):
>>
>>     1. The current draft says that for MPEG-4 ISOBMFF files the language
>>     for audio/video tracks should be: "Content of the language field in
>>     the MediaHeaderBox."
>>     But according to various sources (e.g.
>>
>> https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html
>> ,
>>     https://www.scribd.com/doc/10911307/26/mdhd-box, etc) the language
>>     field in MDHD box is a zero-padded 16-bit value that encodes a
>>     3-letter ISO 639-2/T language code:
>>     3-character code specifying language(see ISO 639-2/T); each character
>>     isinterpreted as 0x60 + (5 bit) code to yield an ASCII character.
>>     Yet according to the HTML5 spec (see
>>
>> https://html.spec.whatwg.org/multipage/embedded-content.html#dom-audiotrack-language
>> )
>>     A/V track language attributes must return BCP-47 language tag strings,
>>     not the 3-character ISO 639-2/T codes.
>>     So the inband-tracks-sourcing spec should probably mention that the
>>     language read from MDHD.language field needs to be translated into
>>     BCP-47.
>>
>>     2. Again, according to multiple sources on the internet (for example
>>     see
>>
>> https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html
>> ).
>>     There is a new way to specify language info for media tracks in MP4
>>     files, see the 'Extended Language Tag Atom' section in the link above.
>>     The ELNG box is optional, but when present it will have a BCP-47
>>     language info. So when the ELNG box is present in the .mp4 file, it
>>     should probably be preferred over the language field of MDHD box.
>>
>>
>>
> --
> Yosuke Funahashi
> Web and TV IG co-chair, Entertainment vertical champion,
> HTML Media Extensions WG team contact at W3C
> Project Associate Professor at Keio University
>