Imported flv becomes slow when playing

I imported a flv video(in_a_club_cut20.flv) to my Animate(dino_in_a_club.fla), length is < 8 seconds, 24fps.

put on stage, modify frame rate to be 20fps

test movie(Control > test movie > in animate ), the video becomes slow, about 1/3 of original speed. I exported a mp4 named dino_in_a_clubTestExpirt.mp4 for your reference.

I tried 24fps and modify Animate file to be 24fps, but it still becomes slow speed.

Please help, thank you

The original speed should be in_a_club_cut.mp4

The .fla is removed automatically by this sit due to the reason above:

Correct the highlighted errors and try again.

• The attachment's dino_in_a_club.fla content type (application/octet-stream) does not match its file extension and has been removed.

I don't know why.