AnimationClip from FBX file can't be loaded from assetbundle.

2486860--171500--u1.png

I have a scriptable object ,which has a reference to the animationclip. like this:

[Serializable]
class A:ScriptableObject{
    public AnimationClip B;
}

I bundle the scriptable file and fbx file together. Then I use WWW.LoadFromCacheOrDownload to load the assetbundle.

But the new loaded animationclip is an empty one.
2486860--171502--u3.png

The load code is like below. the idle_bundle is empty!

using(var w = WWW.loadFromCacheOrDownload(url,path){
yield return www;
var asset = www.assetbundle;
var clips = asset.LoadAllAssets<AnimationClip>();
var idle_bundle = clips[0];
etc.....
}

Is any admin or oldbird here?

New found:
Maybe it’s not the load problem but the bundle problem.
the arthur idle.anim file is 495kb. but after bundle, it is 51kb. That’s why it is empty?
setting is : BuildAssetBundleOptions.UncompressedAssetBundle | BuildAssetBundleOptions.ForceRebuildAssetBundle | BuildAssetBundleOptions.DeterministicAssetBundle