Address the common algorithms (transform setter, RTCRtpTransform)

Author: jan-ivar

index.bs

@@ -93,27 +93,39 @@ partial interface RTCRtpReceiver {
 };
 </pre>
 
-This allows manipulation of encoded frames in the media pipeline
-between the processing steps of an {{RTCRtpSender}}'s underlying
-<dfn>encoder</dfn> and <dfn>packetizer</dfn>, and/or
+This allows manipulation of <dfn>encoded frames</dfn> in the media
+pipeline between the processing steps of an {{RTCRtpSender}}'s
+underlying <dfn>encoder</dfn> and <dfn>packetizer</dfn>, and/or
 between an {{RTCRtpReceiver}}'s underlying <dfn>depacketizer</dfn>
 and <dfn>decoder</dfn>.
 
-## Extension operation ## {#operation}
+The [=encoder=] and [=depacketizer=] each have a
+<dfn>[[transformFrameAlgorithm]]</dfn> internal slot initialized to
+the <dfn>passthrough algorithm</dfn> which, given an [=encoded frame=]
+|frame|, is to return |frame|.
+
+Whenever the [=encoder=] outputs a [=encoded frame|frame=], the user
+agent MUST invoke the [=encoder=].[=[[transformFrameAlgorithm]]=] with
+it and pass the result to the associated [=packetizer=] in place of
+the original frame.
 
-At the time when a codec is initialized as part of the encoder, and the
-corresponding flag is set in the {{RTCPeerConnection}}'s {{RTCConfiguration}}
-argument, ensure that the codec is disabled and produces no output.
+Whenever the [=depacketizer=] outputs a [=encoded frame|frame=], the
+user agent MUST invoke the [=depacketizer=].[=[[transformFrameAlgorithm]]=]
+with it and pass the result to the associated [=decoder=] in place of
+the original frame.
+
+## Extension operation ## {#operation}
 
 At construction of each {{RTCRtpSender}} or {{RTCRtpReceiver}}, run the following steps:
 1. Initialize [=this=].`[[transform]]` to null.
 1. Initialize [=this=].`[[pipeToController]]` to null.
+1. Initialize [=this=].`[[frameSource]]` to [=this=]'s [=encoder=] if [=this=] is an {{RTCRtpSender}} or [=this=]'s [=depacketizer=] otherwise.
 1. [=Queue a task=] to run the following steps:
     1. If [=this=].`[[pipeToController]]` is not null, abort these steps.
-    2. Set [=this=].`[[pipeToController]]` to a new {{AbortController}}.
-        <!-- FIXME: Fix aborting. -->
-        <p class="note">TODO: Specify details of how
-        [=this=].`[[pipeToController]]` aborts streaming in the worker.</p>
+    1. Set [=this=].`[[pipeToController]]` to a new {{AbortController}}.
+    1. Let |frameSource| be [=this=].`[[frameSource]]`.
+    1. [=In parallel=], set |frameSource|.[=[[transformFrameAlgorithm]]=] to the
+        [=passthrough algorithm=].
 
 ### Stream processing ### {#stream-processing}
 
@@ -173,9 +185,7 @@ As [$writeEncodedData$] ensures that the transform cannot reorder frames, this w
 
 ## Extension attribute ## {#attribute}
 
-A RTCRtpTransform has private slots:
-* `[[readable]]` of type {{ReadableStream}}.
-* `[[writable]]` of type {{WritableStream}}.
+An RTCRtpTransform has a private slot:
 * `[[owner]]` of type {{RTCRtpSender}} or {{RTCRtpReceiver}}, initialized to null.
 
 Each RTCRtpTransform has an <dfn abstract-op for=RTCRtpTransform>association steps</dfn> set, which is empty by default.
@@ -185,28 +195,23 @@ The <dfn attribute for="RTCRtpSender,RTCRtpReceiver">transform</dfn> getter step
 
 The `transform` setter steps are:
 1. Let |transform| be the argument to the setter.
-1. Let |checkedTransform| set to |transform| if it is not null or to an [=identity transform stream=] otherwise.
-1. If |checkedTransform|.`[[owner]]` is not null, throw a {{InvalidStateError}} and abort these steps.
-1. Let |reader| be the result of [=ReadableStream/getting a reader=] for |checkedTransform|.`[[readable]]`.
-1. Let |writer| be the result of [=WritableStream/getting a writer=] for |checkedTransform|.`[[writable]]`.
-1. Set |checkedTransform|.`[[owner]]` to [=this=].
+1. If |transform| is not null and |transform|.`[[owner]]` is not null, throw a {{InvalidStateError}} and abort these steps.
+1. Set |transform|.`[[owner]]` to [=this=].
 1. Initialize |newPipeToController| to a new {{AbortController}}.
 1. If [=this=].`[[pipeToController]]` is not null, run the following steps:
-    1. [=AbortSignal/Add=] the [$chain transform algorithm$] to [=this=].`[[pipeToController]]`'s [=AbortController/signal=].
+    1. [=AbortSignal/Add=] the [$apply transform$] to [=this=].`[[pipeToController]]`'s [=AbortController/signal=].
     2. [=AbortController/signal abort=] on [=this=].`[[pipeToController]]`.
-1. Else, run the [$chain transform algorithm$] steps.
+1. Else, run the [$apply transform$] steps.
 1. Set [=this=].`[[pipeToController]]` to |newPipeToController|.
 1. Set [=this=].`[[transform]]` to |transform|.
 1. Run the steps in the set of [$association steps$] of |transform| with [=this=].
 
-The <dfn abstract-op>chain transform algorithm</dfn> steps are defined as:
+The <dfn abstract-op>apply transform</dfn> steps are defined as:
 1. If |newPipeToController|'s [=AbortController/signal=] is [=AbortSignal/aborted=], abort these steps.
-2. [=ReadableStreamDefaultReader/Release=] |reader|.
-3. [=WritableStreamDefaultWriter/Release=] |writer|.
-4. [=Assert=] that |newPipeToController| is the same object as |rtcObject|.`[[pipeToController]]`.
-<!-- FIXME: Use pipeTo algorithm when available. -->
-5. Call <a href="https://streams.spec.whatwg.org/#readable-stream-pipe-to">pipeTo</a> with |rtcObject|.`[[readable]]`, |checkedTransform|.`[[writable]]`, preventClose equal to false, preventAbort equal to false, preventCancel equal to true and |newPipeToController|'s [=AbortController/signal=].
-6. Call <a href="https://streams.spec.whatwg.org/#readable-stream-pipe-to">pipeTo</a> with |checkedTransform|.`[[readable]]`, |rtcObject|.`[[writable]]`, preventClose equal to true, preventAbort equal to true, preventCancel equal to false and |newPipeToController|'s [=AbortController/signal=].
+1. [=Assert=] that |newPipeToController| is the same object as |rtcObject|.`[[pipeToController]]`.
+    <!-- FIXME: Fix aborting. -->
+    <p class="note">TODO: Specify details of how
+    [=this=].`[[pipeToController]]` replaces the transform in the media pipeline.</p>
 
 This algorithm is defined so that transforms can be updated dynamically.
 There is no guarantee on which frame will happen the switch from the previous transform to the new transform.
@@ -931,7 +936,7 @@ The <dfn constructor for="RTCRtpScriptTransform" lt="RTCRtpScriptTransform(worke
 
 Each {{RTCRtpScriptTransform}} has the following set of [$association steps$], given |rtcObject|:
 1. Let |transform| be the {{RTCRtpScriptTransform}} object that owns the [$association steps$].
-1. Let |frameSource| be |rtcObject|'s [=encoder=] if |rtcObject| is an {{RTCRtpSender}} or |rtcObject|'s [=depacketizer=] otherwise.
+1. Let |frameSource| be |rtcObject|'s `[[frameSource=]]`.
 1. [=Queue a task=] on the DOM manipulation [=task source=] |worker|'s global scope to run the following steps:
     1. Let |transformer| be the {{RTCRtpScriptTransformer}} object associated to |transform|.
     1. Set |transformer|.{{[[frameSource]]}} to |frameSource|.