If after loading your video, Mixcraft does one of the following:
If one of the above is happening, it could definitely be the DirectX video decoder. The best advice is to convert your video file into an AVI or WMV. AVI and WMV files are tested to be compatible with Mixcraft. AVI files will use less CPU power, as well.
Search the Internet for "video converter software" that will convert from your video format to AVI and/or WMV.