In media side-edit there are several actions that you can perform by clicking on "Actions" button:
Delete - if status is NOT "Validating" or "Transcoding"'.
By clicking this action a new Edit video file pop-up window will open.
Insert a file before, middle or after the video by adding media from your library.
Trim a file by entering start and end time.
You can insert and trim a file that is not transcoded and has one source video file!
For transcoded assets you can only Extract a new file, by entering new file name and start, end time. Transcoded asset should have one source video file.