Fixing node/video.js to support transparent mov files

[webtonicAI]

I had to make a patch to get a transparent mov file to not show the alpha channel as black. In the video.js file I changed:

Line 53 - this.voImageExtra = conf.voImageExtra === undefined ? 'png' : conf.voImageExtra; //jpg to png

Line 318 - let opts = -loglevel info -start_number 0 -vf fps=${fps},format=rgba -qscale:v ${qscale}.split(' '); //added format=rgba

I'd appreciate if you added this fix to the core project.