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Re: [webrtc-encoded-transform] Need for modifying metadata (#135)

From: Harald Alvestrand via GitHub <sysbot+gh@w3.org>
Date: Wed, 22 Jun 2022 12:41:00 +0000
To: public-webrtc-logs@w3.org
Message-ID: <issue_comment.created-1163048409-1655901658-sysbot+gh@w3.org>
Synchronous = SetMetadata() returns immediately, having affected the metadata
Asynchronous = SetMetadata() (probably) posts a task that performs the modification, and returns a promise that will resolve when the modification is done.
I don't think exposing the attributes as individually mutable makes sense, and having one mutator for each piece of modifiable metadata seems an invitation to interface cruft.

I also imagine that the only time SetMetadata makes sense is after a frame has been created or received, and before enqueueing it to its destination; modifying it at any other time would be a positive invitation to a race condition.

webcodecs (https://w3c.github.io/webcodecs/#encodedvideochunk-interface) seems to have ignored frame-attached metadata. Instead, it chose to emit EncodedVideoChunkMetadata on its callback interface, alongside the video frame itself: https://w3c.github.io/webcodecs/#encoded-video-chunk-metadata

One of the pieces of their metadata is the "VideoDecoderConfig".

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