Currently, we can get keyframes for videos via Document.load_uri_to_video_tensor(only_keyframes=True). However, use-cases typically require us to be able to link keyframes back to the source video. It would be very helpful to be able to:

1. Load the video using load_uri_to_video_tensor
2. Then extract keyframes in a way that retains or outputs the frame number of the keyframes.

This is so that we can access the video at keyframes and extract snippets of film.