[webkit-dev] Position on emerging standard: WebCodecs

Chris Cunningham chcunningham at chromium.org
Wed Feb 10 15:07:54 PST 2021

On Tue, Feb 9, 2021 at 4:20 PM Chris Cunningham <chcunningham at chromium.org>

> +mmaxfield at apple.com, who mentioned similar privacy concerns in a WebGPU
> meeting back in October.
> +jer.noble at apple.com, since we're recently talking about this spec in
> Media WG meetings.
> Hi Group,
> Sorry to revive an old thread! I want to give a few updates.
> One request: please offer replies in the form of github issues. This helps
> us track/scope the feedback.
> https://github.com/WICG/web-codecs/issues
> > (let me know if there is a more detailed proposal).
> The specification is now quite detailed.
> https://wicg.github.io/web-codecs/
> > - Any media pipeline should be off the JS main thread, by default.
> > This does not seem guaranteed by the proposal.
> The spec now mandates that the media pipeline work be offloaded to a
> "codec thread". This may in fact be a fan out of many threads, but is not
> allowed to be the main ("control") thread.
> > Capabilities is indeed an issue. The more you need to understand the
> > codec, the wider is the API and the potential fingerprinting surface.
> The spec has an outstanding PR
> <https://github.com/WICG/web-codecs/pull/120> to add a capabilities API
> like so:
> let supportInfo = await VideoDecoder.isConfigSupported({ codec: 'vp8', ...
> });
> We agree that this adds to the fingerprinting surface. I've added a Privacy
> Considerations section
> <https://wicg.github.io/web-codecs/#privacy-considerations> to describe
> this in more detail and suggest possible mitigations. Happy to discuss this
> more on the github.
> > WebCodec might also potentially expose precise timing information in
> > how long it takes to decode/encode frames. Is it a way to identify
> > which hardware is being used underneath?
> Possibly. Implementers might mitigate by adding artificial delay to emit
> codec outputs.
> Best,
> Chris

Apologies, I'm re-sending because my first attempt bounced for not having
subscribed to this list.
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