How often should an artist release a music video ?  

I think one every 3 months is good. It depends on the artist and genre though. At least two a year should be a minimum but having one per season I think is ideal for most.

I agree about one every 3 months. That will keep your music relevant without working too hard. I think for artists who are touring and doing live events, it is hard to pump out a music video every month. 

If you're just starting out and have an EP or album to promote, it's best to release a music video for each song.

This creates a lot of content that people can find through YouTube searches and browsing, which gives the artist more opportunities for fans to discover their work.

As an artist becomes more successful, they may release one music video every few months or so, or even do a "video-of-the-month" type series to create regular content for fans.

Every other month. I think this is good for newer artists. Once you have an established fanbase, then you can stop releasing so many of them. 

Three months! I feel like that is good enough for most artists. If you are an indie artist or very new, you can benefit from doing more videos. 

I think every 7 months is good for them to come up with their ideas also preparing 

I'd say twice a year. You can do a new one per album/EP as well as a few lyric videos and you are good to go. You don't need to do them that often.