If you want always the same speed when starting the scene, you could set the initialize setting. You'll find it with a right click on the value you like to set. This way the speed will always start at the same speed, when starting the scene, despite it was changed afterwards.

If you want the video to run in a loop, or have multiple speedvariations, you can do a variant of @Michel solution. The inside range in combination with a selector actor can do a variation of two speeds.

If you need more, you can go with Michels solution and use it as many times as you want the speed to change.
An alternative would be the use of the comparator actor.

But the ultimate solution for timed value changes would be the envelope actor. This way you could even do smooth speed changes over time.

<p>but how do I do if I Want control  2 different speed ? <br /></p>

Couldn't you do the same thing, but with 2 of each actor?

If you want to fade the speed up and down, instead of just change, you could use an envelope generator instead of a trigger value actor.

Cheers,

Hugh

but how do I do if I Want control  2 different speed ? 

For exemple : at the beginning of the video, I want a specific speed and at the middle I want another one..

thank you very much for help

Angelique

Yes you can use the "inside range" actor to trigger a "trigger value"

actor.