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Remove Discovery Section #104

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May 16, 2024
Merged

Remove Discovery Section #104

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3a825ef
Remove Discovery Section
aboba May 9, 2024
a8239ec
Remove redundant text
aboba May 9, 2024
6e67b21
Clarify language
aboba May 9, 2024
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93 changes: 47 additions & 46 deletions index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -125,7 +125,7 @@ <h2>Dictionary {{RTCRtpEncodingParameters}} Members</h2>
<p>
A case-sensitive identifier of the scalability mode to be
used for this stream. Scalability modes are defined in
Section 6.
Section 5.
</p>
</dd>
</dl>
Expand Down Expand Up @@ -302,40 +302,26 @@ <h3>{{RTCRtpSender/getParameters()}}</h3>
temporal scalability modes (e.g. [="L1T1"=],[="L1T2"=],[="L1T3"=], etc.).
</p>
</section>
</section>
</section>
<section id="discovery" class="informative">
<h2>Discovery</h2>
<p>
The [[?Media-Capabilities]] API enables discovery of encoder and decoder
support for scalable video coding. {{VideoConfiguration//scalabilityMode}}
is used to query whether an encoder supports a particular
{{RTCRtpEncodingParameters/scalabilityMode}} value. The API indicates
whether the {{RTCRtpEncodingParameters/scalabilityMode}} value
is "supported", "smooth" and "power efficient".
</p>
<p>
The [[?Media-Capabilities]] API also provides information on decoder support
for spatial scalablity modes. {{VideoConfiguration/spatialScalability}}
indicates whether a decoder has the ability to support spatial prediction,
which requires the ability to use frames of a resolution different than
the current resolution as a dependency. If {{VideoConfiguration/spatialScalability}}
is set to <code>true</code>, the decoder can decode any
{{RTCRtpEncodingParameters/scalabilityMode}} value supported by the encoder.
If {{VideoConfiguration/spatialScalability}} is set to <code>false</code>
or is absent, the decoder cannot decode spatial scalability modes, but can
can decode all other {{RTCRtpEncodingParameters/scalabilityMode}} values
supported by the encoder.
</p>
<section id="sfmnegotiation" class="informative">
<h2>Negotiation with an SFM</h2>
<h2>Negotiation issues</h2>
<p>
The <a title="Selective Forwarding Middlebox">SFM</a>
can provide information on the codecs and scalability modes it can
decode by providing its receiver capabilities.
After exchanging capabilities, the application can compute the
intersection of codecs and {{RTCRtpEncodingParameters/scalabilityMode}}
values supported by the browser's {{RTCRtpSender}} and the
SVC is most often employed in video conferencing, where a conferencing
server such as a <a title="Selective Forwarding Middlebox">SFM</a>
selectively forwards layers to participants based on their device
characteristics and available bandwidth. In such an environment,
the application will negotiate codecs to be sent and received with
the conferencing server. However, since scalability modes are not
negotiated in Offer/Answer, the application needs to determine
which scalability modes the conference server supports by other
means.
</p>
<p>
One way to handle this is for the SFM to indicate the codecs
and scalability modes it can decode in the form of receiver
capabilities. After exchanging capabilities, the application
can compute the intersection of codecs and
{{RTCRtpEncodingParameters/scalabilityMode}} values supported
by the browser's {{RTCRtpSender}} and the
<a title="Selective Forwarding Middlebox">SFM</a>'s receiver. This
can be used to determine the arguments passed to the browser's
{{RTCPeerConnection/addTransceiver()}} and {{RTCRtpSender/setParameters()}}
Expand All @@ -362,7 +348,7 @@ <h2>Negotiation with an SFM</h2>
supported, and if so, what scalability modes the
<a title="Selective Forwarding Middlebox">SFM</a> can handle. For example,
an <a title="Selective Forwarding Middlebox">SFM</a> that can only support
reception of a maximum of 2 simulcast encodings on a single SSRC with the
reception of a maximum of two simulcast encodings on a single SSRC with the
AV1 codec would only indicate support for the [="S2T1"=] and [="S2T1h"=] scalability
modes in its receiver capabilities.
</p>
Expand All @@ -379,7 +365,8 @@ <h2>Negotiation with an SFM</h2>
<a title="Selective Forwarding Middlebox">SFM</a> may not be determined until
completion of the Offer/Answer negotiation.
</p>
</section>
</section>
</section>
</section>
<section id="scalabilitymodes*">
<h3>Scalability modes</h3>
Expand All @@ -388,7 +375,7 @@ <h3>Scalability modes</h3>
as well as their associated identifiers and characteristics, are provided in the table
below. The names of the {{RTCRtpEncodingParameters/scalabilityMode}} values (which are
case sensitive) are provided, along with the scalability mode identifiers assigned in
[[?AV1]] Section 6.7.5, and links to dependency diagrams provided in Section 10.
[[?AV1]] Section 6.7.5, and links to dependency diagrams provided in Section 9.
</p>
<p>
While the [[?AV1]] and VP9 [[?VP9]] specifications support all the
Expand Down Expand Up @@ -707,7 +694,7 @@ <h3>Guidelines for addition of {{RTCRtpEncodingParameters/scalabilityMode}} valu
<ol>
<li>
The proposed {{RTCRtpEncodingParameters/scalabilityMode}} MUST define entries to the table in
Section 6, including values for the Scalabilty Mode Identifier, spatial and
Section 5, including values for the Scalabilty Mode Identifier, spatial and
temporal layers, Resolution Ratio, Inter-layer dependency and the corresponding
AV1 scalability_mode_idc value (if assigned).
</li>
Expand All @@ -727,7 +714,7 @@ <h3>Guidelines for addition of {{RTCRtpEncodingParameters/scalabilityMode}} valu
frames have their temporal identifier shifted upward.
</li>
<li>
A dependency diagram MUST be supplied, in the format provided in Section 10.
A dependency diagram MUST be supplied, in the format provided in Section 9.
</li>
</ol>
</section>
Expand Down Expand Up @@ -940,17 +927,31 @@ <h2>Persistent information</h2>
is decodable for the codec in use can be obtained,
which provides more information on hardware capabilities.
</p>
<p>
The [[?Media-Capabilities]] API enables discovery of encoder and decoder
support for scalable video coding. {{VideoConfiguration//scalabilityMode}}
is used to query whether an encoder supports a
{{RTCRtpEncodingParameters/scalabilityMode}} value, indicating whether
it is "supported", "smooth" and "power efficient".
</p>
<p>
The [[?Media-Capabilities]] API also provides information on decoder support
for spatial scalablity modes. {{VideoConfiguration/spatialScalability}}
indicates whether a decoder has the ability to support spatial prediction,
which requires the ability to use frames of a resolution different than
the current resolution as a dependency. If {{VideoConfiguration/spatialScalability}}
is set to <code>true</code>, the decoder can decode any
{{RTCRtpEncodingParameters/scalabilityMode}} value supported by the encoder.
If {{VideoConfiguration/spatialScalability}} is set to <code>false</code>
or is absent, the decoder cannot decode spatial scalability modes, but can
can decode all other {{RTCRtpEncodingParameters/scalabilityMode}} values
supported by the encoder.
</p>
<p>
As noted in [[?Media-Capabilities]] Section 3.1, the Media
Capabilities API "will likely provide more accurate and
consistent information" than is available from the
WebRTC-SVC API. Media Capabilities provides information
on encoder and decoder capabilities, indicating whether
a proposed configuration (including a
{{RTCRtpEncodingParameters/scalabilityMode}} value) is
"supported", "smooth" and "power efficient".
[[?Media-Capabilities]] API also indicates whether the
decoder supports spatial prediction. As noted in
consistent information" than is available from this
specification. As noted in
[[?Media-Capabilities]] Section 3.1, "This information is
expected to have a high correlation with other information
already available to the web pages as a given class of
Expand Down
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