Its better to read JUST this post , it's well explained AND documented with LOT of screenshots!!!
https://www.scirra.com/forum/how-do-i-play-videos-under-android_t167376
Lost 4 full days trying to solve this, with this fantastic problem.............
Develop games in your browser. Powerful, performant & highly capable.
Closing, please always follow the bug report guidelines otherwise as usual we will close without investigation.