Allow transferring ArrayBuffer into VideoFrame, AudioData, EncodedVideoChunk, EncodedAudioChunk, ImageDecoder constructors
Currently when creating any of the VideoFrame, AudioData, EncodedVideoChunk, EncodedAudioChunk, ImageDecoder objects
from corresponding *Init objects constructors make a copy of ArrayBuffer contents into an internal memory buffer.
In many cases the ArrayBuffer is never used again for anything else after a WebCodecs object is created.
It means that this copy can be avoided by transfering (moving) ArrayBuffer contents into the WebCodecs objects.
Remember, memcpy is murder.
Let's add a transfer list to WebCodecs *Init objects, that would allow developers to signal when they don't need
the ArrayBuffer after the object is created. If the transfer list contains the data ArrayBuffer, the ArrayBuffer is detached and
its contents are used in the WebCodecs objects without a copy. This is consistent with the approach taken by structuredClone and postMessage
dictionary VideoFrameBufferInit {
.......
sequence<ArrayBuffer> transfer = [];
};
dictionary ImageDecoderInit {
.....
sequence<ArrayBuffer> transfer = [];
};
dictionary EncodedVideoChunkInit {
.....
sequence<ArrayBuffer> transfer = [];
};
dictionary AudioDataInit {
.....
sequence<ArrayBuffer> transfer = [];
}
dictionary EncodedAudioChunkInit {
.....
sequence<ArrayBuffer> transfer = [];
}
let prototype_frame = new VideoFrame(canvas, { timestamp: 0 });
let size = prototype_frame.allocationSize();
let buf = new ArrayBuffer(size);
let layout = await prototype_frame.copyTo(buf);
let init = {
format: prototype_frame.format,
timestamp: prototype_frame.timestamp,
codedWidth: prototype_frame.codedWidth,
codedHeight: prototype_frame.codedHeight,
layout: layout,
transfer: [buf]
};
// |buf| is transfered here and becomes detached
let new_frame = new VideoFrame(buf, init);
- WebCodecs github issue: w3c/webcodecs#104
- Prototype CL for VideoFrame: https://chromium-review.googlesource.com/c/chromium/src/+/4529012
- w3c Media Working Group discussion: https://www.w3.org/2023/05/30-mediawg-minutes.html#t01