Aspect ratio correction.

Possibly out of scope, but please consider a per-video flag that allows setting a corrected aspect ratio for the uploaded video. E.g. a 4:3 source is erroneously stretched to 16:9. This flag could potentially be utilised by external players and userscripts alike.

YouTube themselves once supported this feature as part of the upload interface, as a special class of tags. E.g. `yt:stretch=4:3`.