Prevent bpsproxy from auto-rotating proxies and making them differ from source files

Mobile devices (iOS, Android), generally write their video in the same orientation always and use only mp4 metadata to indicate rotation.

Blender's behaviour on adding an mp4 with rotation metadata to the sequencer is to ignore the metadata and show the video as written. Thus a mobile video recorded "upside down" would look just fine in any modern player, but will show in the Blender VSE as upside down. This is not impossible to deal with and at least it is consistent.

BUT, when bpsproxy uses ffmpeg to encode the proxy video, ffmpeg's default behaviour on encode is to auto-rotate the resulting file and reset the rotation flag in metadata. When source files are metadata-rotated, this default behaviour results in bpsproxy-produced proxies being oriented differently from their source clips in the VSE. I.e. they show up upside down in the viewer.

I have added -noautorotate to the ffmpeg command line. With this, if a source video is rotated by metadata, the proxy will be in sync. If the source video has no such metadata, then nothing changes and they are in sync.