So i've seen many videos that are basically 1 hour long and contain around 12 songs from different artists, and an image as a background. Almost all of these videos have ads on them which leads me to the following question: Can i also do the same? is it considered fair use?
I think you can buy those song or they are from free sources otherwise i don't think they could monetize it
The ads may have been placed on the video from the original copyright holders of each of the songs and not necessarily by the person creating the mixes. You should not monetize any videos on your account that do not contain material 100% created by you, or that do not have the proper permission from the copyright holders whose material you are taking from.
Taken from the Google support page - Video monetisation criteria - YouTube Help
Examples of content that would NOT be eligible for monetisation
Taken from the Google support page - Video monetisation criteria - YouTube Help
Examples of content that would NOT be eligible for monetisation
- Your video has music that you purchased on iTunes or content that you taped off the television.
- You edit together a compilation of content created by others.