It is at a very high bitrate, at least 8Mbps(1M bytes per second, a 30 seconds video is larger than 40MB). Most of the Wireless environment could not afford such speed. The most important is not the Wireless router itself, but the performance of the Wireless card of Android box.
Maybe you can try to pause on the box for a while ( there is a pause button on our controlling bar if you use the remote controller to bring up the controlling bar) before you play.
I have tested at least 5 Android boxes, while testing, all of my devices is within a distance of 2 meters from the Wireless router:
1) The transfer speed from my iPad2 while sending is about 0.8-1.2M Bytes per second;
2) The speed of 4 of my Android devices while receiving is about 0.6-0.9MB per second, only one reaches 0.9-1.6M per second
so buffering is nearly unavoidable.
By the way, the transfer speed depends on:
1) The performance of Wireless card's CPU;
2) The design of Wireless card's antenna;
3) The encrypt arithmetic: WEP or WPA or OPENED, normally OPENED mode will promote about 10% transfer speed.