How to control the video's viewport in code?

[JamesXu20150314]

Hello,

I want to control the video's viewport in code, but I don't know how to modified the code,
Should I modify the following code:

var update = quat.fromValues(controls.manualRotateRate[0] * interval,
controls.manualRotateRate[1] * interval,
controls.manualRotateRate[2] * interval, 1.0);
quat.normalize(update, update);
quat.multiply(manualRotation, manualRotation, update);

Also, what's the four number's means in manualRotation?

Who could help me. Thank you very much.

Yours Sincerely,
James Xu