Ability to mirror videos

I would love for folks to have the option to mirror videos. This could just be a simple toggle.

Use cases:

• Fitness accounts demonstrating an exercise. Some folks want to see exercises mirrored; others don't.

• A video recorded in selfie mode is flipped, and all the text is backwards.

• Tutorials made for right-handed people can then be easily flipped for lefties (<- this is my personal use case).

This just avoids needing duplicated videos or needing to re-upload.