It's impossible to know whats going on without more details about your workflow. If you import an image sequence, then check the file interpretation to make sure the frame rate is correct, then you create a new comp from the footage and render the comp using any of the standard output module or AME templates your video will be rendered at the same frame rate as the composition.
If your comp plays back at a constant frame rate as indicated by the info panel but the action speeds up then there is a problem with your original footage. AE will not drop frames or change the timing between frames unless you tell it to do so with one of the time effects. When the video seems to speed up check the movement between frames and see if the motion stays constant by stepping through the comp one frame at a time. I'm just guessing here but I suspect that the camera slowed down as the video was being recorded and the time between each frame changed while you were shooting. I am guessing that Magic Lantern was running into frame buffer problems or write speed problems so the frame rate decreased as more time passed.
First of all thank you!
As i come back home i try to put in act your tips.
Meanwhile I can tell you that i made other 3 video with the same prcedure and same duration and I encounter the same identical problem.
Could be a problem I'm shooting in NTSC?