Target: Hotfixes - [x] Add ffmpeg back to the Dockerfile dependencies - [x] Create a management command that: - [x] Loops through all file objects that have an audio or video preset and for which duration is `null` - [x] Gets that file from GCS - [x] Reads the duration from it using ffprobe (example command here: https://github.com/learningequality/ricecooker/blob/develop/ricecooker/utils/videos.py#L107) - [x] Sets that duration on *all* files that share the same MD5