From 8ddd49c215b04078eb673b1dc889ac6f35990a7f Mon Sep 17 00:00:00 2001
From: Florent Castelli <florent.castelli@gmail.com>
Date: Mon, 27 Mar 2023 18:02:55 +0200
Subject: [PATCH] Add a codec match algorithm for setCodecPreferences

Also remove impossible to implement steps in setCodecPreferences,
as it's always possible to modify a dictionary.

Fixes #2845.
---
 webrtc.html | 42 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 34 insertions(+), 8 deletions(-)

diff --git a/webrtc.html b/webrtc.html
index fee0e333b..6390b8ee1 100644
--- a/webrtc.html
+++ b/webrtc.html
@@ -11110,17 +11110,14 @@ <h2>
                 </p>
                 <p>
                   The <var>codecs</var> sequence passed into
-                  {{setCodecPreferences}} can only contain codecs that are
-                  returned by
+                  {{setCodecPreferences}} can only contain
+                  {{RTCRtpCodec}} values that match values using the [= codec match =]
+                  algorithm that are returned by
                   {{RTCRtpSender}}.{{RTCRtpSender/getCapabilities}}(<var>kind</var>)
                   or
                   {{RTCRtpReceiver}}.{{RTCRtpReceiver/getCapabilities}}(<var>kind</var>),
                   where <var>kind</var> is the kind of the
                   {{RTCRtpTransceiver}} on which the method is called.
-                  Additionally, the {{RTCRtpCodecCapability}} dictionary
-                  members cannot be modified. If <var>codecs</var> does not
-                  fulfill these requirements, the user agent MUST [=
-                  exception/throw =] an {{InvalidModificationError}}.
                 </p>
                 <p class="note">
                   Due to a recommendation in [[!SDP]], calls to
@@ -11196,8 +11193,7 @@ <h2>
                       For each <var>codec</var> in <var>codecs</var>,
                     </p>
                     <ol>
-                      <li>If <var>codec</var> is not in
-                      <var>codecCapabilities</var>, throw
+                      <li>If the result of the [= codec match =] algorithm between <var>codec</var> and each of <var>codecCapabilities</var> items is false, throw
                       {{InvalidModificationError}}.
                       </li>
                     </ol>
@@ -11209,6 +11205,36 @@ <h2>
                     </p>
                   </li>
                 </ol>
+                <p>
+                  The <dfn class="export">codec match</dfn> algorithm given two {{RTCRtpCodec}} or compatible dictionaries <var>first</var> and <var>second</var> is as follows:
+                </p>
+                <ol class=algorithm>
+                  <li>
+                    <p>
+                      If <var>first</var>.{{RTCRtpCodec/mimeType}} is different from <var>second</var>.{{RTCRtpCodec/mimeType}}, return <code>false</code>.
+                    </p>
+                  </li>
+                  <li>
+                    <p>
+                      If <var>first</var>.{{RTCRtpCodec/clockRate}} is different from <var>second</var>.{{RTCRtpCodec/clockRate}}, return <code>false</code>.
+                    </p>
+                  </li>
+                  <li>
+                    <p>
+                      If <var>first</var>.{{RTCRtpCodec/channels}} is different from <var>second</var>.{{RTCRtpCodec/channels}}, return <code>false</code>.
+                    </p>
+                  </li>
+                  <li>
+                    <p>
+                      If <var>first</var>.{{RTCRtpCodec/sdpFmtpLine}} is different from <var>second</var>.{{RTCRtpCodec/sdpFmtpLine}}, return <code>false</code>.
+                    </p>
+                  </li>
+                  <li>
+                    <p>
+                      Return <code>true</code>.
+                    </p>
+                  </li>
+                </ol>
                 <p class="note">
                   If set, the offerer's codec preferences will decide the order
                   of the codecs in the offer. If the answerer does not have any