support for replace video source file

Support added for replacing video source file

`v.replace('video_uri', 'myvideo.mp4', 'redirect_url')`
The indentation for this should be cleaned up since it's not really clear that the `upgrade_to_1080` value is there.

I think this is all safe to outdent a bit more so that it's 1 tab in and you'll have space to fit it.