Can iPhone5 to play my own recorded video stored on a flashdrive?
To the best of my knowledge, OTG flash drives come in either microUSB or USB Type-C versions. 

As no past or current model of iPhone or iPad natively support these connections, it's unlikely that OTG flash drives will bundle the software and adapter needed to be used by your iPhone. That's because iOS itself would require specific apps to allow data to be accessed from an external device, and also because it'd need to support a Lightning port connection in some way.

The only options I've seen that would allow you to do what you want, are custom designed solutions specifically targeting iOS devices. For example, there are iPhone cases that include storage and an app to allow the iPhone to use that storage. Likewise there are specific flash drives that do the same.

Below are three examples:


Mophie Space Pack
SanDisk iExpand Flash Drive
Lexar microSD Reader


NOTE: I have not personally used any of these devices - I list them purely as examples of what I'm referring to.