Well, first, I don't watch videos on my phone. I have a laptop and a tablet for that. However, let's assume for the purposes of this discussion that I did...
you lower it's volume, and ALWAYS remember to increase it for the ringtone?
Yes. Not only is changing the volume brain-dead simple, it's also how almost every other device we use on a regular basis works. Commercials too loud on your TV? Turn the volume down, turn it back up when the commercials are over. Car stereo not loud enough with the windows down? Turn the volume up, turn it back down when you roll the windows up.
You don't forget to do that, do you? You don't suffer because the volume is up too loud, do you? No, you adjust the volume. Many times without thinking... your hand almost instinctively grabs the remote, or turns the dial.
This is such a simple thing, such an individualized thing, that I'm almost starting to think you're winding me up on purpose for S&Gs.