Hello,
First of all i'm new in joomla.
I 've installed Allvideos (plugin) and when i play the same video from youtube is working perfect, but when i play it from my local web server it doesn't work, although the music is playing but i see a black screen.
Can you help me ?

I am having same issue with mp4 files. They work fine on mobile device. But on PC i can only hear sound, no video.

Make sure that the format of your video is MP4 (H.264 Video).