After discussion w/ Chrome security / platform folks, we're on board to add SecureContext restrictions to {Audio|Video|Image}Decoder, {Audio|Video}Encoder. We would like to exempt VideoFrame and AudioData. No strong opinion about Encoded{Audio|Video}Chunk.

We used WebGPU's review as a reference gpuweb/gpuweb#1363

similar circumstances: WC adds a little bit of extra fingerprinting surface and grants access to hardware primitives.
similar tradeoffs : Restricting to SecureContext will prevent passive http injection from using WC to fingerprint while slightly raising the bar for folks to use the API.

We also find extensive precedent beyond WebGPU.

What is Chrome's position on new features generally?

That's here. https://www.chromium.org/Home/chromium-security/prefer-secure-origins-for-powerful-new-features

We don't perfectly meet that document's def of "particularly powerful" (e.g. not as clear cut as geolocation), but Chrome security / platform folks increasingly prefer SecureContext by default. As mentioned in gpuweb/gpuweb#1363 (comment), "use SecureContext unless you have a solid reason to do otherwise".

We did not immediately find "solid reasons to do otherwise". The main concerns are adding obstacles for debugging and limiting the reach of the API. Given that localhost is considered secure and ~95% of traffic is now https, we don't anticipate significant issues. If we learn otherwise we will quickly reconsider.

We do find solid reasons to not restrict VideoFrame and AudioData. These do not expose fingerprint nor hw access, and they are useful with existing APIs (outside of encoding) that are not SecureContext restricted. Folks may use VideoFrame with Canvs, ImageBitmap, etc. Similarly, we speculate that WebAudio could use AudioData.

The Encoded{Audio|Video}Chunk interfaces similarly don't expose fingerprint nor hw access, but they also don't seem very useful without access to the decoder interfaces. Could go either way.

[SecureContext] #350

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