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

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fc9355e
Default the generate key frame algorithm to all layers.
jan-ivar Aug 5, 2025
60b6c4a
Rework algorithm to function sans rids as well
jan-ivar Sep 19, 2025
1bf37d2
s/rid/RID/ in one place
jan-ivar Sep 19, 2025
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30 changes: 17 additions & 13 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -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}
Expand Down Expand Up @@ -1003,32 +1004,35 @@ 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. Remove from |layers| all layers that are not {{RTCRtpEncodingParameters/active}}, or whose
corresponding {{RTCRtpSender}} track has ended.
1. If |rid| is not undefined, 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. 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. Remove from |layers| all layers already [=list/contained|found=] in any `[[layers]]` of any tasks in |encoder|.`[[pendingKeyFrameTasks]]`.
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@youennf youennf Oct 2, 2025 •
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Maybe we can do that step first before creating the pending key frame task.

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. 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. If |frame| was generated for a layer
[=list/contained=] in |task|.`[[layers]]`, remove that layer from |task|.`[[layers]]`.
If this causes |task|.`[[layers]]` to become empty, then run the following steps:
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Let's resolve the promise as soon as we have a frame, that way, whether there are multiple key frames or just one, it is consistent.

1. Remove |task| from |encoder|.`[[pendingKeyFrameTasks]]`.
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.
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.
Expand Down