To jump on the back of this topic even if they have no sound and you have the mute button ticked videos will hijack the phones audio and pause what you are listening to in other apps.

I can't then unpause the other media and come back to the video as it will instantly hijack audio again.

I 2nd this bug. I hadn't noticed before but double checked and same result. No sound with mute off or on downloaded saved file. Open link and view from source then I can hear sound.

Semi-related is when you save these videos, the filename is appended with "-silent" which perhaps suggests the wrong stream is being loaded