[Bilal_io]

MediaCapabilites.IsTypeSupported was very unhelpful when used to check if mimetype is supported for encoding instead of decoding. But perhaps that's not what it was created for.

[DaleCurtis]

Yes, it was originally for decoding information only.

https://developer.mozilla.org/en-US/docs/Web/API/MediaCapabi... is on the way. I believe the latest Safari preview has it implemented and Chromium should have it shortly as well.