Many use limit by video number watch.
I also personally use a limit for about 5 videos max.
It cannot be 100% perfect as IPs can be dynamic, but mostly works well.
Best is to have new table in database with fields for IP and videos count.
Then in view_video.php you check for IP, next check this IP in database.
If not exists - you save new record with IP and "1" as video count.
If IP already exists - if videos count is less than your limit - you increase number of video count, if video count exceeds your limit - you assign limit error as smarty variable and use in view video template to show message about video limit.
Suggested is to clear such table (use some time in the past) as it can grow very fast (just one more short mysql query)
I think I posted somewhere sometime little bit more of details, but I'm not sure.
Anyway it's pretty easy for semi experienced programmer, only requires some time, but surely not long hours.