Thanks. I used TexturePacker and adapted my code.
I divided all my sprites to single files (yoshi-slurp_1, yoshi-slurp-2... etc) then used TexturePacker.
I define only one the images (ie, slurp to the right img) and use .flip to get it to the left. flip makes a symmetry.. Since I've centered the foots of my yoshi, that shouldn't cause any problems. That doesn't seems to cause problem with walk action but with tongue stuck action..
When WhitespaceStrip is False, That's works, I can get my yoshi walks.. stucks his tongue in both direction.
When WhitespaceStrip is True, That doesn't work. My yoshi walks in both direction but he can't stuck his tongue in a direction correctly..
I don't know why...
Maybe because AtlasRegion store the whitespace informations but don't apply it then the cast to TextureRegion can't be done..
But Animation takes TextureRegion constructor parameter only.
Packed stripped: http://imageshack.us/photo/my-images/849/game1copie.png/
Packed nonstripped: http://imageshack.us/photo/my-images/836/game1le.png/
I can provide you the entire sources if needed..