It's possible that you have downloaded some form of malware onto your phone. It's possible that it installed on your phone without you bring aware if you visited a website or downloaded an app. Have you installed any new apps in the last few days prior to this happening?
Do you mean you are receiving reverse charge video's which are being downloaded to your phone or do you mean your phone is automatically sending video's to your contacts?
If you find nothing to remove via a scan then if this was my phone I'd create a back up and factory reset which wipes everything and takes it back to the last firmware update.
