What is the ruling on filming a video mocking prayer that has spread among people, and what is the expiation for this sin?

Regretting mocking prayer is a praiseworthy act and the essence of repentance. One must cease the sin, regret it, and resolve not to return to it. You should try to erase the effect of this mockery by publishing another video that shows repentance and glorifies prayer. If you exert your utmost effort in this, your repentance will be accepted, even if some trace of the act remains. As for the friends who participated in it, you should advise them and invite them to repent. If they do not repent, then forsake them for the sake of Allah.