Make generateKeyFrame take a single RID or none. Resolve the promise …

…with the frame timestamp

index.bs

@@ -337,7 +337,7 @@ interface RTCRtpScriptTransformer {
     readonly attribute ReadableStream readable;
     readonly attribute WritableStream writable;
     readonly attribute any options;
-    Promise<undefined> generateKeyFrame(optional sequence <DOMString> rids);
+    Promise<unsigned long long> generateKeyFrame(optional DOMString rid);
     Promise<undefined> sendKeyFrameRequest();
 };
 
@@ -381,9 +381,9 @@ Each RTCRtpScriptTransform has the following set of [=association steps=], given
     1. Set |transformer|.`[[encoder]]` to |encoder|.
     1. Set |transformer|.`[[depacketizer]]` to |depacketizer|.
 
-The <dfn method for="RTCRtpScriptTransformer">generateKeyFrame(|rids|)</dfn> method steps are:
+The <dfn method for="RTCRtpScriptTransformer">generateKeyFrame(|rid|)</dfn> method steps are:
 1. Let |promise| be a new promise.
-1. Run the [=generate key frame algorithm=] with |promise|, |this|.`[[encoder]]` and |rids|.
+1. Run the [=generate key frame algorithm=] with |promise|, |this|.`[[encoder]]` and |rid|.
 1. Return |promise|.
 
 The <dfn method for="RTCRtpScriptTransformer">sendKeyFrameRequest()</dfn> method steps are:
@@ -408,23 +408,24 @@ The <dfn attribute for="RTCRtpScriptTransformer">writable</dfn> getter steps are
 
 ## KeyFrame Algorithms ## {#KeyFrame-algorithms}
 
-The <dfn>generate key frame algorithm</dfn>, given |promise|, |encoder| and |rids|, is defined by running these steps:
+The <dfn>generate key frame algorithm</dfn>, given |promise|, |encoder| and |rid|, is defined by running these steps:
 1. If |encoder| is undefined, reject |promise| with {{InvalidStateError}}, abort these steps.
 1. If |encoder| is not processing video frames, reject |promise| with {{InvalidStateError}}, abort these steps.
-1. If |rids| is defined, validate each of the RID values in |rids|.
-    If any RID value is invalid, reject |promise| with {{NotAllowedError}} and abort these steps.
+1. If |rid| is defined, validate its value. If invalid, reject |promise| with {{NotAllowedError}} and abort these steps.
 1. [=In parallel=], run the following steps:
-    1. Gather a list of video encoders, named |videoEncoders| from |encoder|.
-    1. If |rids| is not empty, remove from |videoEncoders| any video encoder that does not match a value in |rids|.
+    1. Gather a list of video encoders, named |videoEncoders| from |encoder|, ordered according negotiated RIDs if any.
+    1. If |rid| is defined, remove from |videoEncoders| any video encoder that does not match |rid|.
+    1. If |rid| is undefined, remove from |videoEncoders| all video encoders except the first one.
     1. If |videoEncoders| is empty, reject |promise| with {{NotFoundError}} and abort these steps.
         |videoEncoders| is expected to be empty if the corresponding {{RTCRtpSender}} is not active, or the corresponding {{RTCRtpSender}} track is ended.
-    1. For each |rid| in |rids|, run the following substeps:
-        1. Create a pending key frame task called |task| with ||task|.`[[rid]]` set to rid and |task|.`[[promise]]`| set to |promise|.
-        1. If |encoder|.`[[pendingKeyFrameTasks]]` is undefined, initialize |encoder|.`[[pendingKeyFrameTasks]]` to an empty set.
-        1. If |encoder|.`[[pendingKeyFrameTasks]]` contains a task which is matching |rid|, remove |rid| from |rids|.
-        1. Add |task| to |encoder|.`[[pendingKeyFrameTasks]]`.
-    1. If |rids| is not empty, remove from |videoEncoders| any video encoder that does not match a value in |rids|.
-    1. For each |videoEncoder| in |videoEncoders|, instruct |videoEncoder| to generate a key frame for the next provided video frame.
+    1. Let |videoEncoder| be the first encoder in |videoEncoders|.
+    1. If |rid| is undefined, set |rid| to the RID value corresponding to |videoEncoder|.
+    1. Create a pending key frame task called |task| with |task|.`[[rid]]` set to rid and |task|.`[[promise]]`| set to |promise|.
+    1. If |encoder|.`[[pendingKeyFrameTasks]]` is undefined, initialize |encoder|.`[[pendingKeyFrameTasks]]` to an empty set.
+    1. Let |shouldTriggerKeyFrame| be <code>true</code> if |encoder|.`[[pendingKeyFrameTasks]]` contains a task whose `[[rid]]`
+        value which is equal to |rid|, and <code>false</code> otherwise.
+    1. Add |task| to |encoder|.`[[pendingKeyFrameTasks]]`.
+    1. If |shouldTriggerKeyFrame| is <code>true</code>, instruct |videoEncoder| to generate a key frame for the next provided video frame.
 
 For any {{RTCRtpScriptTransformer}} named |transformer|, the following steps are run just before any |frame| is enqueued in |transformer|.`[[readable]]`:
 1. Let |encoder| be |transformer|.`[[encoder]]`.
@@ -433,7 +434,7 @@ For any {{RTCRtpScriptTransformer}} named |transformer|, the following steps are
 1. For each |task| in |encoder|.`[[pendingKeyFrameTasks]]`, run the following steps:
     1. If |frame| was generated by a video encoder identified by |task|.`[[rid]]`, run the following steps:
         1. Remove |task| from |encoder|.`[[pendingKeyFrameTasks]]`.
-        1. Resolve |task|.`[[promise]]` with undefined.
+        1. Resolve |task|.`[[promise]]` with |frame|'s timestamp.
 
 By resolving the promises just before enqueuing the corresponding key frame in a {{RTCRtpScriptTransformer}}'s readable,
 the resolution callbacks of the promises are always executed just before the corresponding key frame is exposed.