Fix/web assembly recorder

[jonklein]

Several fixes & improvements for issues I found in using WebAssemblyRecorder:

• fix audio feedback: set video element to muted

• fix truncated video content: don't terminate the worker immediately, wait for the final message indicating that encoding is complete

• fix video timescale not matching framerate: use setInterval instead of repeated setTimeouts to make sure frames are timed correctly instead of slipping

• add a onVideoProcessStarted callback, which is useful for better synchronization of audio/video from different recorders

• add realtime flag, defaulted to true (current behavior), to allow for non-realtime (higher quality) encoding. this is very slow, but may be useful.

[thijstriemstra]

can you add a new release with this @muaz-khan?

[thijstriemstra]

@jonklein did you test this with Firefox and polyfill, e.g. the online demo? https://www.webrtc-experiment.com/RecordRTC/simple-demos/WebAssemblyRecorder.html

18:14:32.051 TypeError: The stream is not in a state that permits enqueue
readable-stream.ts:1274:12
    enqueue readable-stream.ts:1274
    f RecordRTC.js:6008

It breaks the demo (and my project relying on recordrtc) so I have to revert back to recordrtc 5.5.9 for now unfortunately.

cc @muaz-khan

[thijstriemstra]

screenshot:

[muaz-khan]

@thijstriemstra Please check 1fd3e03 . And test demo again on Firefox.

• https://www.webrtc-experiment.com/RecordRTC/simple-demos/WebAssemblyRecorder.html

[thijstriemstra]

thanks @muaz-khan looks good now.