Not at all an expert at this, but I can try to help.
I have no direct experience with video spin, but if I have no idea what is actually causing a problem when converting a video, the first thing I try is making sure as many of the properties for the output video are the same as the source video as possible. If the program is typical, there should be some way to change the properties of the output file before its generated; if there is no way to choose what those properties are, I recommend finding a different program to work with, as the program trying to "help" you by generating the properties automatically can sometimes be detrimental.
So, try making sure video resolution is the same, that the aspect ratio is the same, the framerate is the same, the bitrate is the same, the codec used is the same, and so forth. If you want to be really sure, do it for the audio properties as well. Don't worry if the options given by the program aren't exactly right, just set them to be as close a match as possible.
If setting the properties doesn't improve the video, find a different program and try again. There are a million free video editors. One is bound to work without too much fuss.