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Reorder Media Flow and Life-cycle sections.
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@jan-ivar
jan-ivar committed Apr 15, 2024
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Expand Up @@ -759,7 +759,84 @@ <h2>{{MediaStreamTrack}}</h2>
</li>
</ol>
<section>
<h3>Life-cycle and Media Flow</h3>
<h3>Media Flow and Life-cycle</h3>
<section>
<h4>Media Flow</h4>
<p>There are two dimensions related to the media flow for a
{{MediaStreamTrackState/"live"}} {{MediaStreamTrack}} : muted / not
muted, and enabled / disabled.</p>
<p><dfn data-export id=
"track-muted">Muted</dfn> refers to the input to the
{{MediaStreamTrack}}. Live samples MUST NOT be made available to a
{{MediaStreamTrack}} while it is [=muted=].</p>
<p>{{Muted}} is outside the control of web applications, but can be observed by
the application by reading the {{MediaStreamTrack/muted}} attribute and listening
to the associated events {{mute}} and {{unmute}}. The reasons for a
{{MediaStreamTrack}} to be muted are defined by its <a>source</a>.</p>
<p>For camera and microphone sources, the reasons to [=muted|mute=] are
[=implementation-defined=]. This allows user agents to implement privacy
mitigations in situations like:
the user pushing a physical mute button on the microphone, the user
closing a laptop lid with an embedded camera, the user toggling a
control in the operating system, the user clicking a mute button in the
[=User Agent=] chrome, the [=User Agent=] (on behalf of the user) mutes, etc.</p>
<p>On some operating systems, microphone access may
get stolen from the [=User Agent=] when another application with higher-audio priority gets access to it,
for instance in case of an incoming phone call on mobile OS. The [=User Agent=] SHOULD provide
this information to the web application through {{MediaStreamTrack/muted}} and
its associated events.</p>

<p>Whenever the [=User Agent=] initiates such an [= implementation-defined=]
change for camera or microphone sources, it MUST queue a
task, using the user interaction task source, to [=set a track's muted
state=] to the state desired by the user.</p>
<div class="note">This does not apply to [=source|sources=] defined in
other specifications. Other specifications need to define their own steps
to [=set a track's muted state=] if desired.</div>
<p>To <dfn class="abstract-op" id="set-track-muted">set a track's muted state</dfn> to
<var>newState</var>, the [=User Agent=] MUST run the following steps:</p>
<ol class="algorithm">
<li>
<p>Let <var>track</var> be the {{MediaStreamTrack}} in
question.</p>
</li>
<li>
<p>If <var>track</var>.{{MediaStreamTrack/[[Muted]]}} is already
<var>newState</var>, then abort these steps.</p>
</li>
<li>
<p>Set <var>track</var>.{{MediaStreamTrack/[[Muted]]}} to
<var>newState</var>.</p>
</li>
<li>
<p>If <var>newState</var> is <code>true</code> let
<var>eventName</var> be {{mute}}, otherwise
{{unmute}}.</p>
</li>
<li>
<p>[=Fire an event=] named <var>eventName</var> on
<var>track</var>.</p>
</li>
</ol>
<p><dfn data-export id="track-enabled" data-lt="track enabled state|enabled" data-lt-noDefault>Enabled/disabled</dfn> on the other hand is
available to the application to control (and observe) via the
{{MediaStreamTrack/enabled}}
attribute.</p>
<p>The result for the consumer is the same in the sense that whenever
{{MediaStreamTrack}} is muted or disabled (or both) the
consumer gets zero-information-content, which means silence for audio
and black frames for video. In other words, media from the source only
flows when a {{MediaStreamTrack}} object is both
unmuted and enabled. For example, a video element sourced by a muted or
disabled {{MediaStreamTrack}} (contained in a
{{MediaStream}} ), is playing but rendering
blackness.</p>
<p>For a newly created {{MediaStreamTrack}} object, the
following applies: the track is always enabled unless stated otherwise
(for example when cloned) and the muted state reflects the state of the
source at the time the track is created.</p>
</section>
<section>
<h4>Life-cycle</h4>
<p>A {{MediaStreamTrack}} has two states in its
life-cycle: live and ended. A newly created
Expand Down Expand Up @@ -897,80 +974,6 @@ <h4>Life-cycle</h4>
<a href="#ends-nostop">end</a> the track.</p>
</li>
</ol>
<h4>Media Flow</h4>
<p>There are two dimensions related to the media flow for a
{{MediaStreamTrackState/"live"}} {{MediaStreamTrack}} : muted / not
muted, and enabled / disabled.</p>
<p><dfn data-export id=
"track-muted">Muted</dfn> refers to the input to the
{{MediaStreamTrack}}. Live samples MUST NOT be made available to a
{{MediaStreamTrack}} while it is [=muted=].</p>
<p>{{Muted}} is outside the control of web applications, but can be observed by
the application by reading the {{MediaStreamTrack/muted}} attribute and listening
to the associated events {{mute}} and {{unmute}}. The reasons for a
{{MediaStreamTrack}} to be muted are defined by its <a>source</a>.</p>
<p>For camera and microphone sources, the reasons to [=muted|mute=] are
[=implementation-defined=]. This allows user agents to implement privacy
mitigations in situations like:
the user pushing a physical mute button on the microphone, the user
closing a laptop lid with an embedded camera, the user toggling a
control in the operating system, the user clicking a mute button in the
[=User Agent=] chrome, the [=User Agent=] (on behalf of the user) mutes, etc.</p>
<p>On some operating systems, microphone access may
get stolen from the [=User Agent=] when another application with higher-audio priority gets access to it,
for instance in case of an incoming phone call on mobile OS. The [=User Agent=] SHOULD provide
this information to the web application through {{MediaStreamTrack/muted}} and
its associated events.</p>

<p>Whenever the [=User Agent=] initiates such an [= implementation-defined=]
change for camera or microphone sources, it MUST queue a
task, using the user interaction task source, to [=set a track's muted
state=] to the state desired by the user.</p>
<div class="note">This does not apply to [=source|sources=] defined in
other specifications. Other specifications need to define their own steps
to [=set a track's muted state=] if desired.</div>
<p>To <dfn class="abstract-op" id="set-track-muted">set a track's muted state</dfn> to
<var>newState</var>, the [=User Agent=] MUST run the following steps:</p>
<ol class="algorithm">
<li>
<p>Let <var>track</var> be the {{MediaStreamTrack}} in
question.</p>
</li>
<li>
<p>If <var>track</var>.{{MediaStreamTrack/[[Muted]]}} is already
<var>newState</var>, then abort these steps.</p>
</li>
<li>
<p>Set <var>track</var>.{{MediaStreamTrack/[[Muted]]}} to
<var>newState</var>.</p>
</li>
<li>
<p>If <var>newState</var> is <code>true</code> let
<var>eventName</var> be {{mute}}, otherwise
{{unmute}}.</p>
</li>
<li>
<p>[=Fire an event=] named <var>eventName</var> on
<var>track</var>.</p>
</li>
</ol>
<p><dfn data-export id="track-enabled" data-lt="track enabled state|enabled" data-lt-noDefault>Enabled/disabled</dfn> on the other hand is
available to the application to control (and observe) via the
{{MediaStreamTrack/enabled}}
attribute.</p>
<p>The result for the consumer is the same in the sense that whenever
{{MediaStreamTrack}} is muted or disabled (or both) the
consumer gets zero-information-content, which means silence for audio
and black frames for video. In other words, media from the source only
flows when a {{MediaStreamTrack}} object is both
unmuted and enabled. For example, a video element sourced by a muted or
disabled {{MediaStreamTrack}} (contained in a
{{MediaStream}} ), is playing but rendering
blackness.</p>
<p>For a newly created {{MediaStreamTrack}} object, the
following applies: the track is always enabled unless stated otherwise
(for example when cloned) and the muted state reflects the state of the
source at the time the track is created.</p>
</section>
<section>
<h3>Tracks and Constraints</h3>
Expand Down

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