Are AMVs considered stealing content?

So recently I've heard someone say something about AMVs that has made me feel a little guilty. I haven't made many AMVs (if you can even call them that) but I do tend to enjoy making them when I have the time. But after hearing this statement, it's made me feel unmotivated. I don't like the idea of stealing or piracy and I try to avoid as often as possible. But now that I think more about it, could AMVs be considered stealing content?
As long as you give credit to wherever it’s due then yer good IMO...