aillez, The average frame rate is around 30 frames per second, when you convert to AMV (Version 3.68) and use high frame rate setting it sets the frame to 12 fps so what the converter does is use every second frame up to the 24th frame and then drops the last 6 frames which causes a skip.
If you convert to AMV using the Medium Frame Rate setting it will convert at 10 frames per second so it will use every third frame up to 30 and not drop any frames at the end.
So although you are losing 2 frames per second the video will be smoother.
Here are the settings I recommend:
