I've trying to convert a video from 60FPS to 50FPS to prevent beat effect, but I fails to do so.
In the Video Output, I change to Nvidia H264, and select "Filters" than "Change FPS", than the source FPS is NTSC and destination FPS PAL. But this don't eliminates the beat effect at all.
How I should do this?
First of all, you probably wanted to resample fps, keeping the duration. Regarding the beat effect, if it was created during video shooting, this is impossible to reduce it this way. You might want to try the video filter "luma stabilizer" by szlldm, just merged into git master of Avidemux. You need to build Avidemux yourself for that or wait until nightly builds get refreshed.
https://avidemux.org/nightly/