diff --git a/index.bs b/index.bs
index e47097a..0d36aeb 100644
--- a/index.bs
+++ b/index.bs
@@ -889,7 +889,7 @@ partial interface DedicatedWorkerGlobalScope {
 interface RTCRtpScriptTransformer : EventTarget {
     // Attributes and methods related to the transformer source
     readonly attribute ReadableStream readable;
-    Promise<unsigned long long> generateKeyFrame(optional DOMString rid);
+    Promise<undefined> generateKeyFrame(optional DOMString rid);
     Promise<undefined> sendKeyFrameRequest();
     // Attributes and methods related to the transformer sink
     readonly attribute WritableStream writable;
@@ -997,32 +997,34 @@ 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. Let |videoEncoders| be a list of video encoders from |encoder|, ordered according to their negotiated RIDs if any.
+    1. If |rid| is not undefined, remove from |videoEncoders| any video encoder that does not match |rid|.
     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|.
+
+        Note: |videoEncoders| is expected to be empty if the corresponding {{RTCRtpSender}} encoding is not
+            {{RTCRtpEncodingParameters/active}}, or the corresponding {{RTCRtpSender}} track is ended.
+
     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>false</code> if |encoder|.`[[pendingKeyFrameTasks]]` contains a task whose `[[rid]]`
-        value is equal to |rid|, and <code>true</code> otherwise.
+        value is either undefined or 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. If |shouldTriggerKeyFrame| is <code>true</code>, then for each |videoEncoder| in |videoEncoders|, instruct
+        |videoEncoder| to generate a key frame for its 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]]`.
-1. If |encoder| or |encoder|.`[[pendingKeyFrameTasks]]` is undefined, abort these steps.
+1. If |encoder| or |encoder|.`[[pendingKeyFrameTasks]]` are 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. If |frame| was generated by a video encoder identified by |task|.`[[rid]]`, or |task|.`[[rid]]` is undefined and
+        all video encoders have generated one frame since the generation of |frame| was triggered, run the following steps:
         1. Remove |task| from |encoder|.`[[pendingKeyFrameTasks]]`.
-        1. Resolve |task|.`[[promise]]` with |frame|'s timestamp.
+        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 video encoders, it is resolved when all of them have generated a key frame.
 
 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.
@@ -1039,16 +1041,16 @@ An additional API on {{RTCRtpSender}} is added to complement the generation of k
 
 <pre class="idl">
 partial interface RTCRtpSender {
-    Promise&lt;undefined&gt; generateKeyFrame(optional sequence &lt;DOMString&gt; rids);
+    Promise&lt;undefined&gt; generateKeyFrame(optional DOMString rid);
 };
 </pre>
 
 ## Extension operation ## {#sender-operation}
 
-The <dfn method for="RTCRtpSender">generateKeyFrame(|rids|)</dfn> method steps are:
+The <dfn method for="RTCRtpSender">generateKeyFrame(|rid|)</dfn> method steps are:
 
 1. Let |promise| be a new promise.
-1. [=In parallel=], run the [$generate key frame algorithm$] with |promise|, |this|'s encoder and |rids|.
+1. [=In parallel=], run the [$generate key frame algorithm$] with |promise|, |this|'s encoder and |rid|.
 1. Return |promise|.
 
 # Privacy and security considerations # {#privacy}