Skip to content

Commit

Permalink
Update introduction section
Browse files Browse the repository at this point in the history 
This removes mention of Media Playback Quality, which isn't
in scope, display capability detection which is solved elsewhere,
and the comparison with isTypeSupported() and canPlayType().

It also makes a few other minor editorial improvements.
  • Loading branch information
@chrisn
chrisn authored Jul 18, 2024
1 parent d91623a commit 1d52c00
Showing 1 changed file with 28 additions and 53 deletions.
81 changes: 28 additions & 53 deletions index.bs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -103,43 +103,18 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
<em>This section is non-normative</em>

<p>
This specification relies on exposing the following sets of properties:
<ul>
<li>
<p>
An API to query the user agent with regards to the decoding and
encoding abilities of the device based on information such as the
codecs, profile, resolution, bitrates, etc. The API exposes
information such as whether the playback should be smooth and power
efficient.
</p>
<p>
The intent of purposes of the decoding capabilities API is to provide
a powerful replacement to API such as
{{MediaSource/isTypeSupported()}} or
{{HTMLMediaElement/canPlayType()}} which are vague and mostly help the
callers to know if something can not be decoded but not how well it
should perform.
</p>
</li>
<li>
<p>
Better information about the display properties such as supported
color gamut or dynamic range abilities in order to pick the right
content for the display and avoid providing HDR content to an SDR
display.
</p>
</li>
<li>
<p>
Real time feedback about the playback so an adaptative streaming can
alter the quality of the content based on actual user perceived
quality. Such information will allow websites to react to a pick of
CPU/GPU usage in real time. It is expected that this will be tackled
as part of the [[media-playback-quality]] specification.
</p>
</li>
</ul>
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>

Expand Down Expand Up @@ -174,7 +149,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte

<p>
The input to the decoding capabilities is represented by a
{{MediaDecodingConfiguration}} dictionary and the input of the encoding
{{MediaDecodingConfiguration}} dictionary and the input to the encoding
capabilities by a {{MediaEncodingConfiguration}} dictionary.
</p>
<p>
Expand Down Expand Up @@ -241,7 +216,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
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 a plain file
represent a configuration that is meant to be used for plain file
playback.</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
Expand Down Expand Up @@ -269,7 +244,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
<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
<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
Expand Down Expand Up @@ -630,14 +605,14 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte

<p>
The <dfn for='AudioConfiguration' dict-member>bitrate</dfn> member
represents the number of average bitrate of the audio track. The bitrate
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>
represents the samplerate of the audio track in. The samplerate is the
number of samples of audio carried per second. samplerate is only
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}}.
Expand Down Expand Up @@ -961,7 +936,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
<a>Document</a>.
</li>
<li>
Let <var>implementation</var> be the implementation of <code>config.keySystemConfiguration.keySystem</code>
Let <var>implementation</var> be the implementation of <code>config.keySystemConfiguration.keySystem</code>.
</li>

<li>
Expand Down Expand Up @@ -1001,11 +976,11 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
<ol>
<li>
Set the {{EME/robustness}} attribute to <code>
config.keySystemConfiguration.audio.robustness</code>
config.keySystemConfiguration.audio.robustness</code>.
</li>
<li>
Set the {{EME/encryptionScheme}} attribute to <code>
config.keySystemConfiguration.audio.encryptionScheme</code>
config.keySystemConfiguration.audio.encryptionScheme</code>.
</li>
</ol>
</li>
Expand All @@ -1029,7 +1004,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
</li>
<li>
Set the {{EME/encryptionScheme}} attribute to <code>
config.keySystemConfiguration.video.encryptionScheme</code>
config.keySystemConfiguration.video.encryptionScheme</code>.
</li>
</ol>
</li>
Expand Down Expand Up @@ -1065,7 +1040,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
</li>
</ol>
</li>
<li>Return <var>access</var></li>
<li>Return <var>access</var>.</li>
</ol>
</p>
</section>
Expand Down Expand Up @@ -1191,7 +1166,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
already be discovered via experimentation with the exception that the
API will likely provide more accurate and consistent information. This
information is expected to have a high correlation with other
information already available to the web pages as a given class of
information already available to web pages as a given class of
device is expected to have very similar decoding/encoding capabilities.
In other words, high end devices from a certain year are expected to
decode some type of videos while older devices may not. Therefore, it is
Expand All @@ -1200,8 +1175,8 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
</p>

<p>
HDR detection is more nuanced. Adding colorGamut, transferFunction, and
hdrMetadataType has the potential to add significant entropy. However,
HDR detection is more nuanced. Adding {{colorGamut}}, {{transferFunction}}, and
{{hdrMetadataType}} has the potential to add significant entropy. However,
for UAs whose decoders are implemented in software and therefore whose
capabilities are fixed across devices, this feature adds no effective
entropy. Additionally, for many cases, devices tend to fall into large
Expand All @@ -1212,7 +1187,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
<p>
If an implementation wishes to implement a fingerprint-proof version of
this specification, it would be recommended to fake a given set of
capabilities (ie. decode up to 1080p VP9, etc.) instead of returning
capabilities (i.e., decode up to 1080p VP9, etc.) instead of returning
always yes or always no as the latter approach could considerably
degrade the user's experience. Another mitigation could be to limit
these Web APIs to top-level browsing contexts. Yet another is to use a
Expand Down Expand Up @@ -1372,7 +1347,7 @@ spec: encrypted-media-draft; for: EME; urlPrefix: https://w3c.github.io/encrypte
</div>

<div class="note">
The following example can also be found in e.g.
The following example can also be found in
<a href="https://codepen.io/miguelao/pen/bWNwej/left?editors=0010#0">
this codepen</a> with minimal modifications.
</div>
Expand Down

0 comments on commit 1d52c00

Please sign in to comment.