Re: Sourcing language information for media tracks

Hi Sergey,

I agree with your changes. There is a pending pull request mentioning 
the elng box (officially defined in ISO/IEC 14496-12), see:
https://github.com/w3c/HTMLSourcingInbandTracks/pull/33

HTH,
Cyril

Le 11/03/2016 02:26, Sergey Volk a écrit :
> 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.
>
>


-- 
Cyril Concolato
Multimedia Group / Telecom ParisTech
http://concolato.wp.mines-telecom.fr/
@cconcolato

Received on Tuesday, 15 March 2016 12:34:19 UTC