Clutter 的 timelimes 怎么理解?

[jiyinyiyong]

尝试去看 Clutter 的时候卡在这上面了, 上面这么解释的
The clutter.Timeline() constructor function takes a duration in milliseconds. The actual number of frames per second requested by the timeline will depend on the behaviour of your entire program, the performance of your hardware, and your monitor's refresh rate. It may even vary over time as conditions change. At best, the new-frame signal will be emitted at your monitor's refresh rate. At worst it will be called once at the start and once at the end of your timeline's duration.
http://www.modrana.org/pyclutter_tutorial/tutorial/html/sec-timelines.html
写在函数里面是这个样子, 特别是括号里的参数
timeline = clutter.Timeline(5000) # milliseconds
按解释的, 实际上是硬件和程序性能决定刷新的频率
那么, 这里的这个参数是做什么用的?
而且我尝试去修改这个参数, 看结果一点差别都没有
那么, clutter 用这样一个 API 怎样精确控制动画的速度参数呢?