1) allow users to upload video and add linked videos
2) user upload video
3) admin edit video and change it to "source type: Link", paste link to YouTube video and save
Result: video folder still keeps MP4 file. If edit video, user (or admin) still can change video type (course) and chose before uploaded MP4 file.
Expected result: If "source type" is changed and video saved, system should delete MP4 file.
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