Animated character with skeleton : publish problem (.MP4)

Hello

I've just downloaded Animate on my PC (21.0), and tested the animated faremer exercise.

When I publish my animated character in .gif, everything is OK. (loop animation)

When I publish it in .MP4, I can only see one image of my farmer. He's not walking anymore.

Am I alone to have this problem ?

Thanks for your help.

Best regards