If you don't own the rights to the media you're advertising, your ad may be flagged for copyright violation. This commonly occurs with music in video ads.
How to fix: If you have permission to use the media, appeal the approval process here. In the description box, inform Facebook that you were given the right to run this media.
Another option to get your ad live is to limit your video to less than 20 seconds. Then, edit your campaign to include the new video and update/relaunch your campaign.