W3C home > Mailing lists > Public > public-html-media@w3.org > April 2014

Re: [MSE] Resolving Bug 24370

From: Jim Ley <jim.ley@gmail.com>
Date: Wed, 2 Apr 2014 08:04:06 +0100
Message-ID: <CA+30114MbEjqQ0RMm+7uveHMxR8=v7BM_AscT20iHoKcn87Zjw@mail.gmail.com>
To: Aaron Colwell <acolwell@google.com>
Cc: "<public-html-media@w3.org>" <public-html-media@w3.org>
On 2 April 2014 01:17, Aaron Colwell <acolwell@google.com> wrote:

> 2. Allowing kind & language to change during playback could result in all
> sorts of added complexity to the HTML5 spec.
>
> *I'd like the people who care about this particular feature to answer the
> following questions so that we can make some progress.*
>
> 1. What do you expect the UA to do when kind and/or language is changed on
> a xxxTrack object?
> 2. Why isn't the language & kind data simply placed in the initialization
> segments instead of only being in a DASH manifest?
> 3. Are there real world, compelling examples that require support for
> language and/or kind to be able to change during playback?
>

Isn't the use case for language being mutable simply live subtitles of a
live "channel" that has programmes in different languages and therefore has
closed captions / subtitles in different languages.   Similarly alternate
audio tracks may also change for similar reasons, and knowing the current
language of a text track or audio stream is important, not just for user,
but also for applications, Spoken Subtitling would require the language of
the text in the subtitles/captions to be able to provide any sort of Text
to speech on it.

In BBC Wales in the UK, broadcasts both in English and Welsh and a live
stream of that will switch between languages.  Hixie's suggestion that
no-one watches long running live broadcast-like TV on the web is I'd say
completely wrong, few do it with the VIDEO element certainly, but that's
where MSE and DASH are coming to help.

The spec currently says "The language of a text
track<http://www.whatwg.org/specs/web-apps/current-work/#text-track-language>
 can change dynamically, in the case of a text
track<http://www.whatwg.org/specs/web-apps/current-work/#text-track>
 corresponding to a
track<http://www.whatwg.org/specs/web-apps/current-work/#the-track-element>
 element."
http://www.whatwg.org/specs/web-apps/current-work/#text-track-language

So it seems the UA problems all need to be addressed for that use case
which is already been a stable part of the spec for many years, so I
believe the UA complexity is a red herring to the question, that is
required to be addressed for both text tracks that change and text tracks
that get added / removed.   I don't particularly see why that is limited to
text track's defined in a Track element but not in-band.

Jim.
Received on Wednesday, 2 April 2014 07:04:34 UTC

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