If I remember corectly at v15 I had the same problem on the animations.. update to AssetStudio.x64.v0.12.49 and should work but still.. animations are frame by frame, no video file from what I remember. Maybe I'm wrong!I think yes.
There are texture2d files and animation clips in the animation asset file. No problem extracting texture2d files which are "individual frames". Got hiccup trying to extract animation clips files. I think the animation clip are not real motion video file rather than a script that combine the "individual frames" for the game. That is what i think, am not a programmer.
Would love to hear it if there are ways to extract the animation clips.
//or not, I was wrong.
AnimationClip not extractable