N.B. Be very careful how you use music on the Web. You can only use material if it is out of copyright (copyright term has expired and is now in the public domain), or if the licence specifically says you may use it in videos and other works. You will need to apply for a licence and give credit to the source. Some sites may charge for the licence, some may not, but a licence must be obtained.
Some music sites state credits are not necessary, but all others require proper acknowledgement of the artist/musician and composer.
Please note that stock music and royalty-free music only apply to US copyright law - it does not apply to South Africa. If using this material in South Africa, you will need to apply for a licence and give credit to the artist/musician and composer.
There are limited exceptions in the SA Copyright Act relating to the use of music for educational or research purposes.
The best option is to use music that is licensed under a Creative Commons licence. The licence must however not be restrictive, e.g. NO DERIVATIVES, as this prevents you from remixing or reusing the music in your video or other works. If you want to use it for commercial purposes, you may not use the Creative Commons licence that says NON-COMMERCIAL, as this means it can only be used for non-commercial purposes.