[whatwg] Proposal: channel attribute on HTMLMediaElement

[Mounir Lamouri]

Hi,

As Wes suggested it recently [1], we need a way for content to be able
to ask for their media to be played in the background. This is
particularly useful on Mobile when applications could have their audio
shut down when they are in the background. However, we can imagine that
someone listening to a web music player might want to keep that music
stream playing when the browser is no longer in the foreground. Also, it
will help browsers to know when to keep media playing or pause them when
a tab is put in the background.

However, that problem is a sub-class or a larger problem about assigning
media elements to a specific channel. This is a problem Firefox OS and
Windows 8 have tackled recently with proprietary extensions to
HTMLMediaElement [2][3]. This is a feature other platforms have, like
Android [4] or PulseAudio (GNU/Linux) [5].

Based on the prior work, Paul Adenot and I tried to figure out the use
cases that would apply on the web.

Our proposal is to add a channel attribute on HTMLMediaElement. That
attribute would give information about the type of channel to use and
thus help the UA to know if the channel should be muted or not based on
the current context. In addition, depending on the type of channel, the
UA could decide to whether or not create a low-latency channel.

There is open question regarding the default behaviour. Our proposal
makes the default behaviour to only play the media when the website is
visible but this is not the common default behaviour and such behaviour
might break some websites. Depending on how critical this
retro-compatibility issue is, we could add a 'Default' state that would
have an undefined behaviour to do whatever retro-compatibility requires.

The proposal is the following:

The channel attribute gives a hint about the type of channel the author
is expecting the UA to use. It is an enumerated attribute that uses the
following keywords and states:

Keyword: media
State: Foreground Media
Fallback: none
Description: To be used for media element that wants to play basic media
such as an audio or video stream that should be paused when the page is
put in the background.

Keyword: background-media
State: Background Media
Fallback: Foreground Media
Description: To be used for media element that wants to play basic media
such as an audio or video stream that should not be paused when the page
is put in the background. Music, podcast or radio players are expected
to use this state.

Keyword: effects
State: Effects
Fallback: Foreground Media
Description: To be used for media element that creates short and quick
effects such as button click, game effects. It is intended to be used
for effects that are being heard while using the page, not for
notifications. When on this state, the media should use a low latency
channel.

Keyword: notification
State: Notification
Fallback: effects
Description: Like the effects state, this intends to be used fort short
and quick media but that require to catch user attention whether the
page is currently visible or not. For example, this state could be used
for a sound notification when there is a new email in the user's inbox.

Keyword: communication
State: Communication
Fallback: Background Media
Description: To be used for media element that transmits real time
communication such as phone calls or VOIP. When on this state, the media
should use a low latency channel.

Keyword: alarm
State: Alarm
Fallback: Notification
Description: To be used for media element that wants to make sure to be
played even if the device is currently muted. Typical use case would be
an alarm clock.

The UA might not support some channels or not allow a specific media
element to use some channels, in which case the fallback state should be
used.

The missing value default is the Foreground Media state.

[1]
http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2013-March/039202.html
[2] https://wiki.mozilla.org/WebAPI/AudioChannels
[3] http://msdn.microsoft.com/en-us/library/windows/apps/hh767375
[4]
https://developer.android.com/reference/android/media/AudioManager.html
(see STREAM_* constants)
[5]
http://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/Developer/Clients/ApplicationProperties#line-58
(see PA_PROP_MEDIA_ROLE)

Thanks,
--
Mounir