Question: If it is illegal to download videos and audios from youtube due to copyright reasons, why are there so many youtube to mp4 and mp3 download websites online?

For example <https://freevideotomp3.com//>, one could reason about them just providing a way for users to download youtube content, letting to these users the responsibility to decide whether they will use it for downloading free or copyrighted content.

However most of these websites (just as youtube-mp3) have an internal cache which stores the already processed mp3/mp4 files, so if users download copyrighted material they will store in their server copyrighted content, thus illegal distribution.

How can these websites live without getting sued by google and friends?

Answer: 
YouTube has commented on this topic in the past, stating (paraphrasing) that due to the amount of information that is uploaded to their sites, it simply cannot monitor whether the files are copyrighted with any accuracy or totality. They do have systems in place for standard due diligence and once they are made aware of copyrighted material, whether through trolling via programs designed to identify it, or by report from actual human beings (employees, artists, the public) the material is removed. That being said, it is often replaced in short order by another user or the same with another "handle". YouTube is not offering the material for consumption, they are only a clearinghouse, such that so long as it is in their disclosures are clear that the practice is not only frowned upon but is a definitive violation of their terms and conditions of use that result in the loss of account access, and they do actually, practice due diligence to help combat it, their exposure is limited at best. The individual who downloads copyrighted material has exposure, as does the individual who uploads it, but it would hardly be worthwhile to prosecute ( civilly or criminally) individual infringements as it is about as common as speeding.
OK, I did some research on youtube-mp3.org and I ran across this: 

> 
> if you want to convert YouTube video to MP3 files, you can do so
>  provided that the material is not copyrighted and you are only using
>  the MP3 file for your own personal use.
> 
> 
> 

That came from this site: <http://www.real.com/resources/youtube-to-mp3-converter/> So this proves my theory was right. If you only download them for your own use, like MP3 player, iPod, etc. You're fine. I can breathe better as well because I was a little anxious about this, because anything I download would/will be for my own private use.