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<pre class='metadata'>
Title: Media Capabilities
Repository: w3c/media-capabilities
Status: ED
ED: https://w3c.github.io/media-capabilities/
TR: https://www.w3.org/TR/media-capabilities/
Shortname: media-capabilities
Level: None
Group: mediawg
Editor: Jean-Yves Avenard, w3cid 115886, Apple Inc. https://www.apple.com/
Editor: Mark Foltz, w3cid 68454, Google Inc. https://www.google.com/, https://github.com/markafoltz
Former Editor: Will Cassella, w3cid 139598, Google Inc. https://www.google.com/
Former Editor: Mounir Lamouri, w3cid 45389, Google Inc. https://www.google.com/
Former Editor: Chris Cunningham, w3cid 114832, Google Inc. https://www.google.com/
Former Editor: Vi Nguyen, w3cid 116349, Microsoft Corporation https://www.microsoft.com/
Abstract: This specification intends to provide APIs to allow websites to make
Abstract: an optimal decision when picking media content for the user. The APIs
Abstract: will expose information about the decoding and encoding capabilities
Abstract: for a given format but also output capabilities to find the best match
Abstract: based on the device's display.
!Participate: <a href='https://github.com/w3c/media-capabilities'>Git Repository.</a>
!Participate: <a href='https://github.com/w3c/media-capabilities/issues/new'>File an issue.</a>
!Version History: <a href='https://github.com/w3c/media-capabilities/commits'>https://github.com/w3c/media-capabilities/commits</a>
</pre>
<pre class='link-defaults'>
spec:html; type:dfn; for:realm; text:global object
</pre>
<pre class='anchors'>
spec: media-source; urlPrefix: https://www.w3.org/TR/media-source/
type: interface
for: MediaSource; text: MediaSource; url: #mediasource
type: method
for: MediaSource; text: isTypeSupported(); url: #dom-mediasource-istypesupported
spec: mediastream-recording; urlPrefix: https://www.w3.org/TR/mediastream-recording/#
type:interface
text: MediaRecorder; url: mediarecorder
spec: mimesniff; urlPrefix: https://mimesniff.spec.whatwg.org/#
type: dfn; text: valid mime type; url: valid-mime-type
</pre>
<pre class='biblio'>
{
"SMPTE-ST-2084": {
"href": "https://ieeexplore.ieee.org/document/7291452",
"title": "High Dynamic Range Electro-Optical Transfer Function of Mastering Reference Displays",
"publisher": "SMPTE",
"date": "2014",
"id": "SMPTE-ST-2084"
},
"SMPTE-ST-2086": {
"href": "https://ieeexplore.ieee.org/document/7291707",
"title": "Mastering Display Color Volume Metadata Supporting High Luminance and Wide Color Gamut Images",
"publisher": "SMPTE",
"date": "2014",
"id": "SMPTE-ST-2086"
},
"SMPTE-ST-2094": {
"href": "https://ieeexplore.ieee.org/document/7513361",
"title": "Dynamic Metadata for Color Volume Transform Core Components",
"publisher": "SMPTE",
"date": "2016",
"id": "SMPTE-ST-2094"
},
"ENCRYPTED-MEDIA-DRAFT": {
"href": "https://w3c.github.io/encrypted-media",
"title": "Encrypted Media Extensions",
"publisher": "W3C",
"date": "13 December 2019"
}
}
</pre>
<section class='non-normative'>
<h2 id='introduction'>Introduction</h2>
<em>This section is non-normative</em>
<p>
This specification defines an API to query the user agent with regards
to its audio and video decoding and encoding capabilities,
based on information such as the codecs, profile, resolution, bitrates,
etc., of the media. The API indicates if the configuration is supported
and whether the playback is expected to be smooth and/or power efficient.
</p>
<p>
This specification focuses on encoding and decoding capabilities.
It is expected to be used with other web APIs that provide information about
the display properties, such as supported color gamut or dynamic range capabilities,
which enable web applications to pick the right content for the display and to,
for example, avoid providing HDR content to an SDR display.
</p>
</section>
<section>
<h2 id='decoding-encoding-capabilities'>Decoding and Encoding Capabilities</h2>
<section>
<h3 id='media-configurations'>Media Configurations</h3>
<section>
<h4 id='mediaconfiguration'>MediaConfiguration</h4>
<xmp class='idl'>
dictionary MediaConfiguration {
VideoConfiguration video;
AudioConfiguration audio;
};
</xmp>
<xmp class='idl'>
dictionary MediaDecodingConfiguration : MediaConfiguration {
required MediaDecodingType type;
MediaCapabilitiesKeySystemConfiguration keySystemConfiguration;
};
</xmp>
<xmp class='idl'>
dictionary MediaEncodingConfiguration : MediaConfiguration {
required MediaEncodingType type;
};
</xmp>
<p>
The input to the decoding capabilities is represented by a
{{MediaDecodingConfiguration}} dictionary and the input to the encoding
capabilities by a {{MediaEncodingConfiguration}} dictionary.
</p>
<p>
For a {{MediaConfiguration}} to be a <dfn>valid
MediaConfiguration</dfn>, all of the following conditions MUST be true:
<ol>
<li>
<code>audio</code> and/or <code>video</code> MUST [=map/exist=].
</li>
<li>
<code>audio</code> MUST be a <a>valid audio configuration</a> if
it [=map/exists=].
</li>
<li>
<code>video</code> MUST be a <a>valid video configuration</a> if
it [=map/exists=].
</li>
</ol>
</p>
<p>
For a {{MediaDecodingConfiguration}} to be a <dfn>valid
MediaDecodingConfiguration</dfn>, all of the following conditions MUST
be true:
<ol>
<li>
It MUST be a <a>valid MediaConfiguration</a>.
</li>
<li>
If <code>keySystemConfiguration</code> [=map/exists=]:
<ol>
<li>
The <code>type</code> MUST be {{media-source}} or {{file}}.
</li>
<li>
If <code>keySystemConfiguration.audio</code> [=map/exists=],
<code>audio</code> MUST also [=map/exist=].
</li>
<li>
If <code>keySystemConfiguration.video</code> [=map/exists=],
<code>video</code> MUST also [=map/exist=].
</li>
</ol>
</li>
</ol>
</p>
<p>
For a {{MediaDecodingConfiguration}} to describe [[!ENCRYPTED-MEDIA]], a
{{keySystemConfiguration}} MUST [=map/exist=].
</p>
</section>
<section>
<h4 id='mediadecodingtype'>MediaDecodingType</h4>
<xmp class='idl'>
enum MediaDecodingType {
"file",
"media-source",
"webrtc"
};
</xmp>
<p>
A {{MediaDecodingConfiguration}} has three types:
<ul>
<li><dfn for='MediaDecodingType' enum-value>file</dfn> is used to
represent a configuration that is meant to be used for playback of
media sources other than {{MediaSource/MediaSource}} as defined in
[[media-source]] and {{RTCPeerConnection}} as defined in [[webrtc]]. </li>
<li><dfn for='MediaDecodingType' enum-value>media-source</dfn> is used
to represent a configuration that is meant to be used for playback of
a {{MediaSource/MediaSource}}. </li>
<li><dfn for='MediaDecodingType' enum-value>webrtc</dfn> is used to
represent a configuration that is meant to be received using
{{RTCPeerConnection}}.</li>
</ul>
</p>
</section>
<section>
<h4 id='mediaencodingtype'>MediaEncodingType</h4>
<xmp class='idl'>
enum MediaEncodingType {
"record",
"webrtc"
};
</xmp>
<p>
A {{MediaEncodingConfiguration}} can have one of two types:
<ul>
<li><dfn for='MediaEncodingType' enum-value>record</dfn> is used to
represent a configuration for recording of media,
<span class="informative">e.g., using {{MediaRecorder}} as defined in
[[mediastream-recording]]</span>.</li>
<li><dfn for='MediaEncodingType' enum-value>webrtc</dfn> is used to
represent a configuration that is meant to be transmitted using
{{RTCPeerConnection}} as defined in [[webrtc]]</span>).</li>
</ul>
</p>
</section>
<section>
<h4 id='mime-type'>MIME types</h4>
<p>
In the context of this specification, a MIME type is also called content
type. A <dfn>valid media MIME type</dfn> is a string that is a <a>valid
MIME type</a> per [[mimesniff]].
</p>
<p>
Please note that the definition of MIME subtypes and parameters is
context dependent. For {{file}}, {{media-source}}, and {{record}}, the
MIME types are specified as defined for [[#http|HTTP]], whereas for
{{MediaDecodingType/webrtc}} the MIME types are specified as
defined for [[#rtp|RTP]].
</p>
<p>
A <dfn>valid audio MIME type</dfn> is a string that is a <a>valid media
MIME type</a> and for which the <code>type</code> per [[RFC9110]] is
either <code>audio</code> or <code>application</code>.
</p>
<p>
A <dfn>valid video MIME type</dfn> is a string that is a <a>valid media
MIME type</a> and for which the <code>type</code> per [[RFC9110]] is
either <code>video</code> or <code>application</code>.
</p>
<section>
<h5 id='http'>HTTP</h5>
<p>
If the MIME type does not imply a codec, the string MUST also have one
and only one parameter that is named <code>codecs</code> with a value
describing a single media codec. Otherwise, it MUST contain no
parameters.
</p>
</section>
<section>
<h5 id='rtp'>RTP</h5>
<p>
The MIME types used with RTP are defined in the specifications of the
corresponding RTP payload formats [[RFC4855]] [[RFC6838]]. The codec
name is typically specified as subtype and zero or more parameters
may be present depending on the codec.
</p>
</section>
</section>
<section>
<h4 id='videoconfiguration'>VideoConfiguration</h4>
<xmp class='idl'>
dictionary VideoConfiguration {
required DOMString contentType;
required unsigned long width;
required unsigned long height;
required unsigned long long bitrate;
required double framerate;
boolean hasAlphaChannel;
HdrMetadataType hdrMetadataType;
ColorGamut colorGamut;
TransferFunction transferFunction;
DOMString scalabilityMode;
boolean spatialScalability;
};
</xmp>
<p>
The <dfn for='VideoConfiguration' dict-member>contentType</dfn> member
represents the MIME type of the video track.
</p>
<p>
To check if a {{VideoConfiguration}} <var>configuration</var> is a
<dfn>valid video configuration</dfn>, the following steps MUST be run:
<ol>
<li>
If <var>configuration</var>'s {{VideoConfiguration/contentType}} is
not a <a>valid video MIME type</a>, return <code>false</code> and
abort these steps.
</li>
<li>
If {{VideoConfiguration/framerate}} is not finite or is not greater
than 0, return <code>false</code> and abort these steps.
</li>
<li>
If an optional member is specified for a {{MediaDecodingType}} or
{{MediaEncodingType}} to which it's not applicable, return
<code>false</code> and abort these steps. See applicability rules
in the member definitions below.
<li>
Return <code>true</code>.
</li>
</ol>
</p>
<p>
The <dfn for='VideoConfiguration' dict-member>width</dfn> and
<dfn for='VideoConfiguration' dict-member>height</dfn> members represent
respectively the visible horizontal and vertical encoded pixels in the
encoded video frames.
</p>
<p>
The <dfn for='VideoConfiguration' dict-member>bitrate</dfn> member
represents the average bitrate of the video track given in units of bits
per second. In the case of a video stream encoded at a constant bit rate
(CBR) this value should be accurate over a short term window. For the
case of variable bit rate (VBR) encoding, this value should be usable to
allocate any necessary buffering and throughput capability to
provide for the un-interrupted decoding of the video stream over the
long-term based on the indicated {{VideoConfiguration/contentType}}.
</p>
<p>
The <dfn for='VideoConfiguration' dict-member>framerate</dfn> member
represents the framerate of the video track. The framerate is the number
of frames used in one second (frames per second). It is represented as a
double.
</p>
<p>
The <dfn for='VideoConfiguration' dict-member>hasAlphaChannel</dfn> member
represents whether the video track contains alpha channel information. If
true, the encoded video stream can produce per-pixel alpha channel information
when decoded. If false, the video stream cannot produce per-pixel alpha channel
information when decoded. If undefined, the UA should determine whether the
video stream encodes alpha channel information based on the indicated
{{VideoConfiguration/contentType}}, if possible. Otherwise, the UA should
presume that the video stream cannot produce alpha channel information.
</p>
<p>
If present, the <dfn for='VideoConfiguration' dict-member>hdrMetadataType</dfn>
member represents that the video track includes the specified HDR
metadata type, which the UA needs to be capable of interpreting for tone
mapping the HDR content to a color volume and luminance of the output
device. Valid inputs are defined by {{HdrMetadataType}}. hdrMetadataType is
only applicable to {{MediaDecodingConfiguration}} for types {{media-source}}
and {{file}}.
</p>
<p>
If present, the <dfn for='VideoConfiguration' dict-member>colorGamut</dfn>
member represents that the video track is delivered in the specified
color gamut, which describes a set of colors in which the content is
intended to be displayed. If the attached output device also supports
the specified color, the UA needs to be able to cause the output device
to render the appropriate color, or something close enough. If the
attached output device does not support the specified color, the UA
needs to be capable of mapping the specified color to a color supported
by the output device. Valid inputs are defined by {{ColorGamut}}. colorGamut
is only applicable to {{MediaDecodingConfiguration}} for types
{{media-source}} and {{file}}.
</p>
<p>
If present, the <dfn for='VideoConfiguration' dict-member>transferFunction</dfn>
member represents that the video track requires the specified transfer
function to be understood by the UA. Transfer function describes the
electro-optical algorithm supported by the rendering capabilities of a
user agent, independent of the display, to map the source colors in the
decoded media into the colors to be displayed. Valid inputs are defined
by {{TransferFunction}}. transferFunction is only applicable to
{{MediaDecodingConfiguration}} for types {{media-source}} and {{file}}.
</p>
<p>
If present, the <dfn for='VideoConfiguration' dict-member>scalabilityMode</dfn>
member represents the scalability mode as defined in [[webrtc-svc]]. If
absent, the implementer defined default mode for this
{{VideoConfiguration/contentType}} is assumed (i.e., the mode you get if
you don't specify one via {{RTCRtpSender/setParameters()}}).
scalabilityMode is only applicable to {{MediaEncodingConfiguration}} for
type {{MediaEncodingType/webrtc}}.
</p>
<p>
If present, the <dfn for='VideoConfiguration' dict-member>spatialScalability</dfn>
member represents the ability to do spatial prediction, that is,
using frames of a resolution different than the current resolution as
dependencies. If absent, spatialScalability will default to
<code>false</code>. spatialScalability is closely coupled to
{{VideoConfiguration/scalabilityMode}} in the sense that streams encoded
with modes using spatial scalability (e.g. "L2T1") can only be decoded
if spatialScalability is supported. spatialScalability is only
applicable to {{MediaDecodingConfiguration}} for types {{media-source}},
{{file}}, and {{MediaDecodingType/webrtc}}.
</p>
</section>
<section>
<h4 id='hdrmetadatatype'>HdrMetadataType</h4>
<p>
<xmp class='idl'>
enum HdrMetadataType {
"smpteSt2086",
"smpteSt2094-10",
"smpteSt2094-40"
};
</xmp>
<p>
If present, {{HdrMetadataType}} describes the capability to interpret HDR metadata
of the specified type.
</p>
<p>
The {{VideoConfiguration}} may contain one of the following types:
<ul>
<li>
<dfn for='HdrMetadataType' enum-value>smpteSt2086</dfn>,
representing the static metadata type defined by
[[!SMPTE-ST-2086]].
</li>
<li>
<dfn for='HdrMetadataType' enum-value>smpteSt2094-10</dfn>,
representing the dynamic metadata type defined by
[[!SMPTE-ST-2094]].
</li>
<li>
<dfn for='HdrMetadataType' enum-value>smpteSt2094-40</dfn>,
representing the dynamic metadata type defined by
[[!SMPTE-ST-2094]].
</li>
</ul>
</p>
</p>
</section>
<section>
<h4 id='colorgamut'>ColorGamut</h4>
<p>
<xmp class='idl'>
enum ColorGamut {
"srgb",
"p3",
"rec2020"
};
</xmp>
<p>
The {{VideoConfiguration}} may contain one of the following types:
<ul>
<li>
<dfn for='ColorGamut' enum-value>srgb</dfn>, representing the
[[!sRGB]] color gamut.
</li>
<li>
<dfn for='ColorGamut' enum-value>p3</dfn>, representing the DCI
P3 Color Space color gamut. This color gamut includes the
{{ColorGamut/srgb}} gamut.
</li>
<li>
<dfn for='ColorGamut' enum-value>rec2020</dfn>, representing
the ITU-R Recommendation BT.2020 color gamut. This color gamut
includes the {{ColorGamut/p3}} gamut.
</li>
</ul>
</p>
</p>
</section>
<section>
<h4 id='transferfunction'>TransferFunction</h4>
<p>
<xmp class='idl'>
enum TransferFunction {
"srgb",
"pq",
"hlg"
};
</xmp>
<p>
The {{VideoConfiguration}} may contain one of the following types:
<ul>
<li>
<dfn for='TransferFunction' enum-value>srgb</dfn>, representing
the transfer function defined by [[!sRGB]].
</li>
<li>
<dfn for='TransferFunction' enum-value>pq</dfn>, representing the
"Perceptual Quantizer" transfer function defined by
[[!SMPTE-ST-2084]].
</li>
<li>
<dfn for='TransferFunction' enum-value>hlg</dfn>, representing the
"Hybrid Log Gamma" transfer function defined by BT.2100.
</li>
</ul>
</p>
</p>
</section>
<section>
<h4 id='audioconfiguration'>AudioConfiguration</h4>
<xmp class='idl'>
dictionary AudioConfiguration {
required DOMString contentType;
DOMString channels;
unsigned long long bitrate;
unsigned long samplerate;
boolean spatialRendering;
};
</xmp>
<p>
The <dfn for='AudioConfiguration' dict-member>contentType</dfn> member
represents the MIME type of the audio track.
</p>
<p>
To check if a {{AudioConfiguration}} <var>configuration</var> is a
<dfn>valid audio configuration</dfn>, the following steps MUST be run:
<ol>
<li>
If <var>configuration</var>'s {{AudioConfiguration/contentType}} is
not a <a>valid audio MIME type</a>, return <code>false</code> and
abort these steps.
</li>
<li>
Return <code>true</code>.
</li>
</ol>
</p>
<p>
The <dfn for='AudioConfiguration' dict-member>channels</dfn> member
represents the audio channels used by the audio track. channels is only
applicable to the decoding types {{media-source}}, {{file}}, and
{{MediaDecodingType/webrtc}} and the encoding type
{{MediaEncodingType/webrtc}}.
</p>
<p class='issue'>
The {{AudioConfiguration/channels}} needs to be defined as a
<code>double</code> (2.1, 4.1, 5.1, ...), an <code>unsigned short</code>
(number of channels) or as an <code>enum</code> value. The current
definition is a placeholder.
</p>
<p>
The <dfn for='AudioConfiguration' dict-member>bitrate</dfn> member
represents the average bitrate of the audio track. The bitrate
is the number of bits used to encode a second of the audio track.
</p>
<p>
The <dfn for='AudioConfiguration' dict-member>samplerate</dfn>
member represents the sample rate of the audio track. The sample rate
is the number of samples of audio carried per second. samplerate is only
applicable to the decoding types {{media-source}}, {{file}}, and
{{MediaDecodingType/webrtc}} and the encoding type
{{MediaEncodingType/webrtc}}.
</p>
<p class='note'>
The {{AudioConfiguration/samplerate}} is expressed in <code>Hz</code>
(ie. number of samples of audio per second). Sometimes the samplerates
value are expressed in <code>kHz</code> which represents the number of
thousands of samples of audio per second.<br>
44100 <code>Hz</code> is equivalent to 44.1 <code>kHz</code>.
</p>
<p>
The <dfn for='AudioConfiguration' dict-member>spatialRendering</dfn>
member indicates that the audio SHOULD be rendered spatially. The
details of spatial rendering SHOULD be inferred from the
{{AudioConfiguration/contentType}}. If it does not [=map/exist=], the UA
MUST presume spatial rendering is not required. When <code>true</code>,
the user agent SHOULD only report this configuration as
{{MediaCapabilitiesInfo/supported}} if it can support spatial
rendering for the current audio output device without failing back to a
non-spatial mix of the stream. {{spatialRendering}} is only applicable to
{{MediaDecodingConfiguration}} for types {{media-source}} and {{file}}.
</p>
</section>
</section>
<section>
<h4 id='mediacapabilitieskeysystemconfiguration'>
MediaCapabilitiesKeySystemConfiguration
</h4>
<xmp class='idl'>
dictionary MediaCapabilitiesKeySystemConfiguration {
required DOMString keySystem;
DOMString initDataType = "";
MediaKeysRequirement distinctiveIdentifier = "optional";
MediaKeysRequirement persistentState = "optional";
sequence<DOMString> sessionTypes;
KeySystemTrackConfiguration audio;
KeySystemTrackConfiguration video;
};
</xmp>
<p class='note'>
This dictionary refers to a number of types defined by
[[ENCRYPTED-MEDIA]] (EME). Sequences of EME types are
flattened to a single value whenever the intent of the sequence was to
have {{Navigator/requestMediaKeySystemAccess()}} choose a subset it supports.
With MediaCapabilities, callers provide the sequence across multiple
calls, ultimately letting the caller choose which configuration to use.
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>keySystem</dfn>
member represents a {{MediaKeySystemAccess/keySystem}} name as described in
[[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>initDataType</dfn>
member represents a single value from the {{MediaKeySystemConfiguration/initDataTypes}} sequence
described in [[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>distinctiveIdentifier</dfn>
member represents a {{MediaKeySystemConfiguration/distinctiveIdentifier}} requirement as
described in [[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>persistentState</dfn>
member represents a {{MediaKeySystemConfiguration/persistentState}} requirement as described in
[[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>sessionTypes</dfn>
member represents a sequence of required {{MediaKeySystemConfiguration/sessionTypes}} as
described in [[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>audio</dfn> member
represents a {{KeySystemTrackConfiguration}} associated with the {{AudioConfiguration}}.
</p>
<p>
The <dfn for='MediaCapabilitiesKeySystemConfiguration' dict-member>video</dfn> member
represents a {{KeySystemTrackConfiguration}} associated with the {{VideoConfiguration}}.
</p>
</section>
<section>
<h4 id='keysystemtrackconfiguration'>
KeySystemTrackConfiguration
</h4>
<xmp class='idl'>
dictionary KeySystemTrackConfiguration {
DOMString robustness = "";
DOMString? encryptionScheme = null;
};
</xmp>
<p>
The <dfn for='KeySystemTrackConfiguration' dict-member>robustness</dfn>
member represents a {{MediaKeySystemMediaCapability/robustness}} level
as described in [[!ENCRYPTED-MEDIA]].
</p>
<p>
The <dfn for='KeySystemTrackConfiguration' dict-member>encryptionScheme</dfn>
member represents an {{MediaKeySystemMediaCapability/encryptionScheme}}
as described in [[!ENCRYPTED-MEDIA-DRAFT]].
</p>
</section>
<section>
<h3 id='media-capabilities-info'>Media Capabilities Information</h3>
<xmp class='idl'>
dictionary MediaCapabilitiesInfo {
required boolean supported;
required boolean smooth;
required boolean powerEfficient;
};
</xmp>
<xmp class='idl'>
dictionary MediaCapabilitiesDecodingInfo : MediaCapabilitiesInfo {
required MediaKeySystemAccess keySystemAccess;
MediaDecodingConfiguration configuration;
};
</xmp>
<xmp class='idl'>
dictionary MediaCapabilitiesEncodingInfo : MediaCapabilitiesInfo {
MediaEncodingConfiguration configuration;
};
</xmp>
<p>
A {{MediaCapabilitiesInfo}} has associated <dfn dict-member
for='MediaCapabilitiesInfo'>supported</dfn>, <dfn dict-member
for='MediaCapabilitiesInfo'>smooth</dfn>, <dfn dict-member
for='MediaCapabilitiesInfo'>powerEfficient</dfn> fields which are
booleans.
</p>
<p>
Encoding or decoding is considered <dfn>power efficient</dfn> when the
power draw is optimal. The definition of optimal power draw for encoding
or decoding is left to the user agent. However, a common implementation
strategy is to consider hardware usage as indicative of optimal power
draw. User agents SHOULD NOT mark hardware encoding or decoding as power
efficient by default, as non-hardware-accelerated codecs can be just as
efficient, particularly with low-resolution video. User agents SHOULD
NOT take the device's power source into consideration when determining
encoding power efficiency unless the device's power source has side
effects such as enabling different encoding or decoding modules.
</p>
<p>
A {{MediaCapabilitiesDecodingInfo}} has associated
<dfn dict-member for=MediaCapabilitiesDecodingInfo>keySystemAccess</dfn>
which is a {{MediaKeySystemAccess}} or <code>null</code> as
appropriate.
</p>
<p class='note'>
If the encrypted decoding configuration is supported, the
resulting {{MediaCapabilitiesInfo}} will include a
{{MediaKeySystemAccess}}. Authors may use this to create
{{MediaKeys}} and setup encrypted playback.
</p>
<p>
A {{MediaCapabilitiesDecodingInfo}} has an associated <dfn
dict-member for='MediaCapabilitiesDecodingInfo'>configuration</dfn> which
is the decoding configuration properties used to generate the
{{MediaCapabilitiesDecodingInfo}}.
</p>
<p>
A {{MediaCapabilitiesEncodingInfo}} has an associated <dfn dict-member
for='MediaCapabilitiesEncodingInfo'>configuration</dfn> which
is the encoding configuration properties used to generate the
{{MediaCapabilitiesEncodingInfo}}.
</p>
<section>
<h3 id='info-algorithms'>Algorithms</h3>
<section>
<h4 id='create-media-capabilities-encoding-info'>
<dfn>Create a MediaCapabilitiesEncodingInfo</dfn>
</h4>
<p>
Given a {{MediaEncodingConfiguration}} <var>configuration</var>, this
algorithm returns a {{MediaCapabilitiesEncodingInfo}}. The following
steps are run:
<ol>
<li>
Let <var>info</var> be a new {{MediaCapabilitiesEncodingInfo}}
instance. Unless stated otherwise, reading and writing apply to
<var>info</var> for the next steps.
</li>
<li>
Set {{MediaCapabilitiesEncodingInfo/configuration}} to be a
new {{MediaEncodingConfiguration}}. For every property in <var>
configuration</var> create a new property with the same name and
value in {{MediaCapabilitiesEncodingInfo/configuration}}.
</li>
<li>
If the user agent is able to encode the media represented by
<var>configuration</var>, set {{MediaCapabilitiesInfo/supported}}
to <code>true</code>. Otherwise set it to <code>false</code>.
</li>
<li>
If the user agent is able to encode the media represented by
<var>configuration</var> at the indicated framerate, set
{{MediaCapabilitiesInfo/smooth}} to <code>true</code>. Otherwise
set it to <code>false</code>.
</li>
<li>
If the user agent is able to encode the media represented by
<var>configuration</var> in a [=power efficient=] manner, set
{{MediaCapabilitiesInfo/powerEfficient}} to <code>true</code>.
Otherwise set it to <code>false</code>.
</li>
<li>
Return <var>info</var>.
</li>
</ol>
</p>
</section>
<section>
<h4 id='create-media-capabilities-decoding-info'>
<dfn>Create a MediaCapabilitiesDecodingInfo</dfn>
</h4>
<p>
Given a {{MediaDecodingConfiguration}} <var>configuration</var>, this
algorithm returns a {{MediaCapabilitiesDecodingInfo}}. The following
steps are run:
<ol>
<li>
Let <var>info</var> be a new {{MediaCapabilitiesDecodingInfo}}
instance. Unless stated otherwise, reading and writing apply to
<var>info</var> for the next steps.
</li>
<li>
Set {{MediaCapabilitiesDecodingInfo/configuration}} to be a new
{{MediaDecodingConfiguration}}. For every property in <var>
configuration</var> create a new property with the same name and
value in {{MediaCapabilitiesDecodingInfo/configuration}}.
</li>
<li>
If <code>configuration.keySystemConfiguration</code> [=map/exists=]:
<ol>
<li>
Set {{MediaCapabilitiesDecodingInfo/keySystemAccess}}
to the result of running the <a>Check Encrypted Decoding
Support</a> algorithm with <var>configuration</var>.
</li>
<li>
If {{MediaCapabilitiesDecodingInfo/keySystemAccess}}
is not <code>null</code> set
{{MediaCapabilitiesInfo/supported}} to
<code>true</code>. Otherwise set it to <code>false</code>.
</li>
</ol>
</li>
<li>
Otherwise, run the following steps:
<ol>
<li>
Set {{MediaCapabilitiesDecodingInfo/keySystemAccess}}
to <code>null</code>.
</li>
<li>
If the user agent is able to decode the media represented
by <var>configuration</var>, set
{{MediaCapabilitiesInfo/supported}} to <code>true</code>.
</li>
<li>Otherwise, set it to <code>false</code>.</li>
</ol>
</li>
<li>
If the user agent is able to decode the media represented by
<var>configuration</var> at the indicated framerate
without dropping frames, set {{MediaCapabilitiesInfo/smooth}}
to <code>true</code>. Otherwise set it to <code>false</code>.
</li>
<li>
If the user agent is able to decode the media represented by
<var>configuration</var> in a [=power efficient=]
manner, set {{MediaCapabilitiesInfo/powerEfficient}} to
<code>true</code>. Otherwise set it to <code>false</code>.
</li>
<li>
Return <var>info</var>.
</li>
</ol>
</p>
</section>
<section>
<h4 id='is-encrypted-decode-supported'>
<dfn>Check Encrypted Decoding Support</dfn>
</h4>
<p>
Given a {{MediaDecodingConfiguration}} <var>config</var> where
{{keySystemConfiguration}} [=map/exists=], this algorithm returns a
{{MediaKeySystemAccess}} or <code>null</code> as appropriate. The
following steps are run:
<ol>
<li>
If the {{keySystem}} member of
<code>config.keySystemConfiguration</code> is not one of the
[=Key Systems=] supported by the user agent, return
<code>null</code>. String comparison is case-sensitive.
</li>
<li>
Let <var>origin</var> be the [=/origin=] of the calling context's
<a>Document</a>.
</li>
<li>
Let <var>implementation</var> be the implementation of <code>config.keySystemConfiguration.keySystem</code>.
</li>
<li>
Let <var>emeConfiguration</var> be a new
{{MediaKeySystemConfiguration}}, and initialize it as follows:
</li>
<ol>
<li>
Set the {{MediaKeySystemConfiguration/initDataTypes}} attribute to a sequence containing
<code>config.keySystemConfiguration.initDataType</code>.
</li>
<li>
Set the {{MediaKeySystemConfiguration/distinctiveIdentifier}} attribute to
<code>config.keySystemConfiguration.distinctiveIdentifier</code>.
</li>
<li>
Set the {{MediaKeySystemConfiguration/persistentState}} attribute to
<code>config.keySystemConfiguration.peristentState</code>.
</li>
<li>
Set the {{MediaKeySystemConfiguration/sessionTypes}} attribute to
<code>config.keySystemConfiguration.sessionTypes</code>.
</li>
<li>
If {{MediaConfiguration/audio}} [=map/exists=] in <var>config</var>, set the
{{MediaKeySystemConfiguration/audioCapabilities}} attribute to a sequence containing a
single {{MediaKeySystemMediaCapability}}, initialized as
follows:
<ol>
<li>
Set the {{MediaKeySystemMediaCapability/contentType}} attribute to
<code>config.audio.contentType</code>.
</li>
<li>
If <code>config.keySystemConfiguration.audio</code>
[=map/exists=]:
<ol>
<li>
Set the {{MediaKeySystemMediaCapability/robustness}} attribute to <code>
config.keySystemConfiguration.audio.robustness</code>.
</li>
<li>
Set the {{MediaKeySystemMediaCapability/encryptionScheme}} attribute to <code>
config.keySystemConfiguration.audio.encryptionScheme</code>.
</li>
</ol>
</li>
</ol>
</li>
<li>
If {{MediaConfiguration/video}} [=map/exists=] in <var>config</var>, set the
videoCapabilities attribute to a sequence containing a single
{{MediaKeySystemMediaCapability}}, initialized as follows:
<ol>
<li>
Set the {{MediaKeySystemMediaCapability/contentType}} attribute to
<code>config.video.contentType</code>.
</li>
<li>
If <code>config.keySystemConfiguration.video</code> [=map/exists=]:
<ol>
<li>
Set the {{MediaKeySystemMediaCapability/robustness}} attribute to <code>
config.keySystemConfiguration.video.robustness</code>.
</li>
<li>
Set the {{MediaKeySystemMediaCapability/encryptionScheme}} attribute to <code>
config.keySystemConfiguration.video.encryptionScheme</code>.
</li>
</ol>
</li>
</ol>
</li>
</ol>
<li>
Let <var>supported configuration</var> be the result of
executing the [=Get Supported Configuration=]
algorithm on <var>implementation</var>,
<var>emeConfiguration</var>, and <var>origin</var>.
</li>