Problem with my iphone regarding videos

Hi
I have a problem with my Iphone 6 S with the latest IOS (13.3). When I want to watch a video on the apple tv app, the volume of the audio and Voiceover increases quite a bit. When i go out of the video the volume resets to the volume i had before. This also happens when I watch a video on the "sky go" app. The strange thing is that when I want to watch something on youtube everything is normal.
Does anyone have this problem, and if so, is there a fix for it?
Thanks,
Matteo