Rndering and recording mirrored video stream from camera.

[stepancar]

Description
Added a demo which demonstrates rendering and recording mirrored video stream from camera.

Purpose

Mirroring video is a common case in video processing.
#1626
This demo shows advantage of processing video frame-by-frame in a worker
https://stepancar.github.io/webrtc-samples/src/content/insertable-streams/video-recording/

[hthetiot]

@stepancar I was wondering if you could add the work around to make MediaRecorder recorded video seekable part the of sample. Doing so would inform developers that implement recording of the issue and potentially serve as reference to push Chromium team reconsider the Won't Fix state of the bug (I can always dream) if all other non chromium browsers proves not having the issue.

I would understand if you refuse, at least mentioning that recording file may not be seekable from this sample when using Chromium based browser can in my point of view go in the right direction and help the cause.

Chrome related WontFix bug:

• https://bugs.chromium.org/p/chromium/issues/detail?id=642012

Know working workaround:

• https://github.com/buynao/webm-duration-fix

[stepancar]

@hthetiot , I would be happy do that too, but when I get any comments from maintainers to make sure this sample makes sense

[stepancar]

@fippo , could you review it? Thank you