Guidance for user-defined VideoFrameMetadata entries

[chrisn]

Web developers could use the VideoFrameMetadata dictionary to store their own custom metadata. Should we provide guidance in the spec or the registry, e.g., on naming convention, so developers avoid conflicts with platform-defined entries?

[chrisn]

Metadata is copied both when passed to the VideoFrame constructor and when returned from metadata() so applications can use any custom dictionary entries without affecting the browser's no behaviour, even if they use the same names. An application might need to rename its own metadata entries if a new registry entry is defined with a name they're using and they want to use both. So could be worth giving developer advice to use something like an underscore prefix for their own metadata values?

[Djuffin]

Frankly I'm not sure that this the intended use for VF metadata. I would only copy metadata members known to the UA.

dictionary VideoFrameMetadata {
  // Possible members are recorded in the VideoFrame Metadata Registry.
};

[Djuffin]

cc @aboba @padenot for opinion

[aboba]

The WebCodecs specification indicates that metadata dictionary entries are epected to be recorded in the VideoFrame Metadata Registry. But do we really expect the UA to only support dictionary members recorded in the Registry? This seems like a maintenance (and interop) headache. Supporting all dictionary members (including custom ones) seems simpler.

[padenot]

I seem to recall professionals in the industry requesting metadata pass-through. Or was it @youennf ?

It's harmless enough to simply forward them.

[Djuffin]

Media WG: let's have a note in the metadata registry along the lines

This registry will never have entries starting with `some prefix`

I'll check if the existing web standards have precedence for such prefixes