FF (Fast Forward) Speed, what governs it ?

[NX3]

I've got a couple of Sony Bravia tv's, 2010 and 2011 series, PS3, Asus O!play, all let you FF at x 3 speed from Serviio. I just assumed this was a DLNA limit as they all have the same max speed. We also have a WDTV which I don't often use but playing around with it today it let FF the same mkv file up to x16 !!

What governs how fast a device can fast forward ? x3 is good but a little faster would be really neat.

[zip]

the client sends requests for bytes range, that's it. So up to the client what kind of ranges it chooses to send.