Videos were not occasionaly autplayed in Viewer

[FrankMejzlik]

Problem:
Sometimes when task started, video didn't start automatically.

Reason:

1. Viewer window didn't have any interaction yet and such window cannot autoplay unmuted video in Chrome.
2. Ontimeupdate callback was called before video was in playable state which caused exception.

Solution:

1. Check promise and catch exceptions. Have video muted by default and unmute it afterwards.
2. Check if video is in a playable state in ontimeupdate callback.

[FrankMejzlik]

Fixed in branch "FIX_handle-play-promise-properly-according-to-new-chrome-version".

[klschoef]

Frank, we have one question:
in case the promise is rejected and the video is muted and played again, do you think that the functionality of looping and blurring etc. will still work?

[FrankMejzlik]

I tested that and realized that this approach does not always work (at least not in my Chrome 78.0.3904.108) and sometimes video hasn't started playing after all.

So I took another approach - by default I marked video HTML tag as muted so the browser will autoplay them without complaining and I call unmuteVideo() afterwards.

At least in Chrome it should be guaranteed that muted video tags are allowed to autoplay even without window interaction.
Source: https://developers.google.com/web/updates/2017/09/autoplay-policy-changes

I pushed the new branch with this tiny change: FIX_use-muted-video-with-unmute-call-if-possible.

With this, I wasn't able to get to the state where a video was not autoplayed correctly.