Unfortunately, we don't have a callback you can use to determine when it stops showing the loading screen.
You can try doing this:
Subscribe like normal. However, have the video displayed OFF the screen (1x1 pixel in -1, -1 coordinates). Have the audio set to mute. Wait 10 seconds to make sure the loading bar is gone. Then put the video on the page, un-mute the audio, and start keeping track of time. You can then determine when the user starts actually seeing the video. Basically start timing them 10 seconds after they subscribe. You can put a little loading bar yourself that goes away after 10 seconds.
Was this post helpful?