Given the direction of gaming and streaming, your mp4 example seems apt... I think being able to do a 1080p stream at 30-60fps in JS is an appropriate goal for both hardware, and software. Canvas+JS is likely to be the "thin" client structure or the future... I think if it were possible to do this in JS, we wouldn't need ignorant plugin points for DRM.. encrypted streaming could "just work" on any platform, not that I want more DRM.
I like that we are finally at a point, where legacy emulators in JS are a reality. I do think some attention to worker interaction, and perhaps locking say a canvas, or audio channel to a worker should be something able to be done.
I think being able to do a 1080p stream at 30-60fps in JS is an appropriate goal
Why is that an appropriate goal? How about a video element -- which the browser implements in the ideal manner (which is usually a thin layer over hardware decoding) -- that handles h264? Why in the world would you want to do that in JavaScript, besides as a "because I can" challenge?
Further your notion that DRM would "just work" is really unclear. I don't think you understand the concerns of the DRM folks if you think that you'll just do it in decrypt.js and all will be good.
I like that we are finally at a point, where legacy emulators in JS are a reality. I do think some attention to worker interaction, and perhaps locking say a canvas, or audio channel to a worker should be something able to be done.