fix: video having no duration (with recordrtc dependency from GitHub)

[marob]

When recording the presentation, the resulting video is corrupted as the duration is not/incorrectly detected by video players.

This issue explains the problem and gives a solution: we have to wrap the blob in getSeekableBlob function.

An important thing to note is that getSeekableBlob function requires EBML as dependency.

I have developed several PR solving the problem and using different ways to import EBML as each of them have pros and cons.

This PR imports recordrtc dependency twice (second time from GitHub URL instead of from npm registry) in order to have the required EBML.js file (which is not packed in the npm registry version of recordrtc)
Cons: we declare the same dependency twice and we use GitHub dependency (not a good practice?).

See other PRs:

• fix: video having no duration (with CDN) #489
• fix: video having no duration (with ts-ebml dependency from GitHub) #491

[antfu]

Thanks but I'd prefer to have this fixed upstream.