1. It doesn't matter that you didn't intend to infringe copyright; you did. If you truly did not intend to infringe copyright, you should have done some research on copyright law and how to make sure you don't break it, intentionally or otherwise. You get lots of helpful information by clicking "copyright" in the yellow box at the top of this page, or by asking a legal expert.

2. Just because other people's videos are fine doesn't mean yours will be. They may have purchased a licence to use the material, or simply been lucky enough not to have been caught out (but their luck could run out any moment).

3. For the record: Copyright law protects every creative work of artistic or literary merit. This includes not just music, but photographs and other images, including the ones you find with Google Image Search.