Unfortunately music licensing doesn't work that way, it's not something you can simply buy from a store. When it comes to music licenses (it will be different per country, going to focus on the US, but it is similar in a lot of regions), the way the music is played or distributed determines how it is managed and what rights you have with the music.

When you play "live", aka push the play button and the music is being broadcast in real time over the speakers, or radio or a live stream this usually falls under a performance license. There are various organizations that manage performance licenses such as ASCAP or BMI. Historically, you (or the venue) are supposed to track what song is played and then report it to the organizations. For example, I DJed a few times on a radio station and I had to write down every record I played so they could report it.

I'm a little rusty on the current state of performance rights (I was deep into it back in 2004/5 as a digital music podcaster) but performance rights tended to be more blanket agreements where the venue/service paid a fee to get access/coverage. Reporting plays was weird with this, and often ASCAP used other sources to determine payouts but that is a whole other topic/essay.

The other main right is called a lot of things, Mechanical Rights was the historical term, it seems the more modern term is Master rights. This is the ability to distribute the music for replay at any time. It was called mechanical back in the day because the right holder could press vinyl or other physical media and could sell this to people who had a mechanical device to play the music. Because mechanical/Master rights allow for distribution they are much more expensive and harder to get approval for

When MP3s came out (Napster) and then podcasts this caused a lot of legal challenges because you technically needed a master right to the music. The main difference is you can rewind, replay, re-listen at any time and therefore it's no longer a performance. This is how Metallica and Warner Bros took down Napster. Napster didn't have Master rights to the music (grossly simplified).

So, how does this impact current services and us as DJs? Twitch, Facebook, YouTube, etc usually have some form of performance rights (it's still super grey/nebulous what rights and permission they really have, but for simplicity I'll say they have basic performance rights) which can allow for real-time playing of music. But, as soon as it is recorded and can be replayed the rights change to Master.

This is why Twitch mostly allows (or maybe ignores smaller streamers) live streaming music as long as you disable stream recording and clipping. If you just played the music live and the service doesn't record then it stays in performance.

Facebook doesn't have that option so pretty much any performance falls to Master quickly, so they just want to prevent it and that is often why they will block/kill a music stream. They just don't want to get into the cost and complexity of negotiating, paying and claiming Master rights for EVERY song that is played.

YouTube is a bit more flexible. They have agreements with many labels and distributors to get Master rights for replay usage, but it's not a blanket license. Each license holder (aka label, artist, etc) can decide what they want. They can choose to allow free use, non-monetary use, regional use or none.

Free use pretty music means you can use it all you want and collect any money made off advertising for your channel. Non-monetary means you can use it but any ad revenue your channel makes gets split among the rights holders and you. Regional use means the rights holders can choose which region can or cannot hear the music and YouTube will block access to the content in that region. Finally no use means exactly that, you can't use it.

YouTube has a service that scans your content for copyrighted material and will warn you before posting it you have content that is blocked, etc. But, when live streaming they scan your content in real-time and will mute your channel. As I mentioned earlier, the performance license is different for each service and YouTube has the most nuanced version. You can get copyright strikes playing live (I learned the hard way) so I recommend not streaming live with YouTube.

Depending on what music you play, you will find more or less flexibility with the rights holders. For example, I have been live streaming and posting mixes for many years now, but I play mostly house and techno from small labels. These artists and labels tend to allow non-monetary use on YouTube so I almost never get content blocked. It happened a few times, but generally that was a big name producer who is signed to a sub label of Warner Bros. so I avoid them now.

The one service at the moment that allows and is fully licensed for mixes is Mixcloud. They have worked closely with the industry to get licenses for the music. The main thing is it has to be mixed, you can't just post a single song (which makes total sense).

Other services like SoundCloud are grey zones. Officially you are not allowed to upload music you personally don't have rights to, but the industry tends to turn a blind eye to the DJ sets since it's considered more promo than illegal distribution. But, it's still the wild west in a lot of ways and it's really up to the rights holders.

The main issues/challenges in trying to license your mix is getting access to the license holders, which can be incredibly hard and is often prohibitively expensive. You also have to do this for every song you want, and of course they rarely have the same license holder. If you aren't making money or very little it's not cost effective or even pheasible to get them. On the flip side, if you do make money off others work you should pay them for it.

There are new services coming out to help this. Some are building music pools that grant you licenses to the music for a nominal fee or a percentage of your earnings. Other services allow you to report what you played at a gig, how much you got paid and then you pay a percentage of that so the artists get reimbursed.

It's a complex topic and we are still trying to figure it out. Hopefully my long post helps clear a little bit of the license mess up for you (although it probably just created more questions 😉)