If you just record a video with the default video/camera app on your phone, Google photos (assuming you have the app and have it set to auto backup at default quality) will back it up on the cloud.
If you have to stop recording before having the video backed up, all a bad actor needs to do is physically destroy your device, and you'll lose your evidence.
As it happens, such apps seem to already exist. Another comment in this thread: https://news.ycombinator.com/item?id=10284629