From one of the answer in Copy synced videos in/from Dailymotion,
Go to the cache, and find the file that you want to play. There will be 2 files with the same name, one will be only a few kb, the other will be the video (should be a few MB).
Long press on the file until you get the menu. Then select "open as", then "video", then select a video player.
I did that process, but when I select "video", after buffering it shows a dialogue that says "Can't play this video".
Any solution to this problem?