[Bug 24859] New: Automatic Video and Audio Track Selection Based on User Preferences and Terminal Characteristics

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24859

            Bug ID: 24859
           Summary: Automatic Video and Audio Track Selection Based on
                    User Preferences and Terminal Characteristics
           Product: HTML WG
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: CR HTML5 spec
          Assignee: robin@w3.org
          Reporter: oipfjon@gmail.com
        QA Contact: public-html-bugzilla@w3.org
                CC: public-html-admin@w3.org

This issue is raised on behalf of HbbTV - see http://www.hbbtv.org, an
organisation specifying the use of web technologies in television receivers.
HbbTV is in the process of adding the HTML5 video element to its specification.
The current HbbTV specification uses the <object> element for presenting video
in an HTML page.

The HTML5 spec defines automatic track selection based on user preferences for
text tracks as follows;

http://www.w3.org/TR/html5/embedded-content-0.html#perform-automatic-text-track-selection

Specifically;

"If the user has expressed an interest in having a track from candidates
enabled based on its text track kind, text track language, and text track
label,"

There is no equivalent language for video and audio tracks. Further, for video
tracks and audio tracks, the resource fetch algorithm includes the following;

"If either the media resource or the address of the current media resource
indicate a particular set of audio or video tracks to enable, then the selected
audio tracks must be enabled in the element's audioTracks object, and, of the
selected video tracks, the one that is listed first in the element's
videoTracks object must be selected. All other tracks must be disabled."

The last sentence of this can be interpreted as excluding the UA selecting
video or audio tracks based on user preferences and/or terminal
characteristics.

We have two use-cases where automatic track selection based on user preferences
and other terminal characteristics for video and audio tracks is important.

1) In TV receivers, typically users can set a range of preferences in the
receiver for preferred audio language, preferred subtitle language and other
audio and subtitle preferences related to accessibility (e.g. a preference for
so-called "clean" audio or for audio tracks including description). These
preferences are held in the receiver and applied automatically by the receiver
for broadcast television. The user can also change these dynamically, for
example depending on the sound track of a particular TV show. In our current
specification, the media player underlying the <object> element follows these
preferences automatically unless the HTML page over-rides it. This particular
use-case is very related to audio. It is generally believed that a single
consistent way of setting these kind of preferences for TV (regardless of how
it is delivered) benefits users.

2) Our current specification supports MPEG DASH for HTTP adaptive streaming.
The MPEG DASH manifest file (MPD) can contain multiple "adaptation sets" (sets
of interchangeable encoded versions of a media component) which can differ in
terms of codec, DRM, language, kind (called "role" by MPEG) and for audio,
number of channels, e.g. stereo / 5.1 / 7.1. In our current specification, the
DASH player automatically selects which video and audio adaptation set to
present based on user preferences and terminal characteristics such supported
codec / DRM and the number of audio channels on the output - stereo, 5.1 or
7.1. The adaptation sets are made visible to apps as our equivalent of
VideoTracks and AudioTracks so that an app can over-ride the automatic
selection if it so desires. We are deliberately not very prescriptive about how
the automatic track selection works and there are a number of situations when
an app might want to over-ride it.

Given these use-cases, we would appreciate your feedback about whether the
HTML5 specification does indeed exclude automatic track selection for video and
audio tracks based on user preferences and terminal characteristics. If this is
excluded, can you please say if this is deliberate or accidental? If it's
deliberate, can you please share the reasons for this? 

If it is excluded, can you to consider removing this exclusion.

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Received on Friday, 28 February 2014 15:44:54 UTC