Performance and Mechanical Royalties from Youtube

So a lot of us are protecting our music rights through Content ID programs like AdRev. It looks like Youtube uses the Content ID system to also collect both performance and mechanical royalties as well, though they are paid out through other entities (Performing rights organizations, and mechanical rights publishers like Songtrust).

With performing rights I understand most broadcasters have a blanket license with the PROs to be able to use all their music in their catalogs. Youtube I know has blanket licenses with ASCAP and BMI for example. This means that the performance royalties paid comes right from Youtube rather than the individual content creators who are purchasing our music, hence still fitting the qualification of ‘royalty-free’ for our youtube customers, and the majority of our other customers as well.

My question that I’m wondering about, if anyone can answer for me, is how do mechanical royalties work? Do they work like performance royalties where the broadcasters pay out a blanket license, or do these mechanical royalties come out of the pockets of the content owners themselves? Trying to decide if something like Songtrust (mechanical rights collection) would be appropriate to register our AJ music with.

Thanks guys!