Default the generate key frame algorithm to all layers. (#276)

* Default the generate key frame algorithm to all layers and use infra more

Author: jan-ivar

index.bs

@@ -53,6 +53,7 @@ spec:webidl; type:dfn; text:resolve
 </pre>
 <pre class=link-defaults>
 spec:streams; type:interface; text:ReadableStream
+spec:infra; type:dfn; text:list
 </pre>
 
 # Introduction # {#introduction}
@@ -1028,32 +1029,36 @@ The <dfn abstract-op>generate key frame algorithm</dfn>, given |promise|, |encod
     in Section 10 of [[!RFC8851]], then reject |promise| with {{TypeError}} and abort
     these steps.
 1. [=In parallel=], run the following steps:
-    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, [=queue a task=] to 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. 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. Let |layers| be a new [=list=] of the layers for this |encoder|, ordered by negotiated encoding index.
+    1. [=list/Remove=] from |layers| all layers that are not {{RTCRtpEncodingParameters/active}}, or whose
+        corresponding {{RTCRtpSender}} track has ended.
+    1. If |rid| is not undefined, [=list/remove=] from |layers| all layers whose RID is not |rid|.
+
+       Note: If no |rid| is passed in, keyframes are generated for all active layers.
+
+    1. If |layers| is now empty, [=queue a task=] to reject |promise| with {{NotFoundError}} and abort these steps.
+    1. [=list/Remove=] from |layers| all layers already [=list/contained|found=] in any `[[layers]]` of any tasks in |encoder|.`[[pendingKeyFrameTasks]]`.
+    1. Create a pending key frame task called |task| with |task|.`[[layers]]` set to |layers| and |task|.`[[promise]]` set to |promise|.
     1. If |encoder|.`[[pendingKeyFrameTasks]]` is undefined, initialize |encoder|.`[[pendingKeyFrameTasks]]` to an empty set.
-    1. Let |shouldTriggerKeyFrame| be <code>false</code> if |encoder|.`[[pendingKeyFrameTasks]]` contains a task whose `[[rid]]`
-        value is equal to |rid|, and <code>true</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.
+    1. [=set/Append=] |task| to |encoder|.`[[pendingKeyFrameTasks]]`.
+    1. For each |layer| in |layers| (if any), instruct |encoder| to generate a key frame for its
+        next provided video frame to that |layer|.
 
 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]]`.
 1. If |encoder| or |encoder|.`[[pendingKeyFrameTasks]]` is undefined, abort these steps.
 1. If |frame| is not a video {{RTCEncodedVideoFrameType/"key"}} frame, abort these steps.
 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. If |frame| was generated for a layer [=list/contained=] in |task|.`[[layers]]`,
+        then run the following steps:
+        1. [=list/Remove=] that layer from |task|.`[[layers]]`.
+        1. If |task|.`[[layers]]` is now empty, then [=list/remove=] |task| from
+            |encoder|.`[[pendingKeyFrameTasks]]`.
+        1. [=Resolve=] |task|.`[[promise]]` with undefined.
 
 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.
-If the promise is associated to several rid values, it will be resolved when the first key frame corresponding to one the rid value is enqueued.
+If the promise is associated with several layers, it will be resolved once key frames have been enqueued for all of them.
 
 The <dfn abstract-op>send request key frame algorithm</dfn>, given |promise| and |depacketizer|, is defined by running these steps:
 1. If |depacketizer| is undefined, reject |promise| with {{InvalidStateError}}, abort these steps.