It's neither a high-throughput filesystem nor responsive to sluggishness.

That is, a system that is designed to stream video will respond to congestion or other slowness by lowering quality. Reading a file directly from a normal network filesystem is going to skip and jerk and pause and otherwise screw up when something bad happens, which it will.

I guess what I'm saying is that for a DVD player app, you don't really care about every little piece of data. If you miss a few, it's not so bad. You want it to keep progressing in real time through the media. On the other hand, SMB is going to try to get you every bit of data, in order, no matter how long it takes, and no matter if that one bit halfway through is going to take three hours, blocking the rest. (Obviously, the app could do more random file access than that, but something like WiMP isn't going to.)