RTCRtpScriptTransformer: writable property
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
The writable
read-only property of the RTCRtpScriptTransformer
interface returns a WritableStream
instance that can be used as a sink for encoded media frames enqueued on the corresponding RTCRtpScriptTransformer.readable
.
When the corresponding RTCRtpScriptTransform
is inserted into the WebRTC sender and receiver pipelines, encoded media frames (RTCEncodedVideoFrame
or RTCEncodedAudioFrame
) may be enqueued on the RTCRtpScriptTransformer.readable
.
A WebRTC encoded transform can read the frames from readable
, modify them as needed, and then send them back into the WebRTC pipeline by sending them to this writable
.
A common way to perform this operation is to pipe the frames through a TransformStream
.
Value
Examples
The following example shows how RTCRtpScriptTransformer.readable
is piped through a TransformStream
to RTCRtpScriptTransformer.writable
.
addEventListener("rtctransform", (event) => {
let transform;
// Select a transform based on passed options
if (event.transformer.options.name == "senderTransform")
transform = createSenderTransform(); // A TransformStream
else if (event.transformer.options.name == "receiverTransform")
transform = createReceiverTransform(); // A TransformStream
else return;
// Pipe frames from the readable to writeable through TransformStream
event.transformer.readable
.pipeThrough(transform)
.pipeTo(event.transformer.writable);
});
The code implements a handler for the rtctransform
event, which is fired at the global worker object on construction of the corresponding RTCRtpScriptTransform
, and when new frames are enqueued for processing.
event.transformer
is the RTCRtpScriptTransformer
that has the writable
and readable
properties.
An different TransformStream
is created to process outgoing and incoming frames, using createSenderTransform()
or createReceiverTransform()
, respectively (implementations not shown).
The event handler chooses the correct transform stream to use based on options passed through from the RTCRtpScriptTransform
constructor and assigns it to transform
.
The code calls ReadableStream.pipeThrough()
on the readable
to pipe encoded frames through the selected TransformStream
, and then ReadableStream.pipeTo()
to pipe them to the RTCRtpScriptTransformer.writable
.
Specifications
Specification |
---|
WebRTC Encoded Transform # dom-rtcrtpscripttransformer-writable |
Browser compatibility
BCD tables only load in the browser