I don't use quicktime BUT this may help
If movies do not play properly, check the QuickTime connection speed setting.
In Windows and Mac OS 9 or earlier, open the QuickTime Settings in Control Panel, then choose Connection Speed from the pop-up menu.
In Mac OS X, open System Preferences, then click QuickTime. Click the Connection tab to select a speed. It may be that the speed is not set to your BB download rate.
I hope that this helps
If you select a speed slower than your actual connection speed, QuickTime will always try to locate and play versions of the movie authored for the closest match to the slower connection speed. (The resulting movie may be smaller in size and lower in quality than your connection can actually support.)
If you select a speed faster than your actual connection, QuickTime playback may stutter or appear jerky.