What key/time signature is this song in?

[Bespinben]

It's absolutely not swing. There are running triplets constantly throughout the entire piece, as well as some syncopated rhythms in the melody that would only make sense in compound time. Use a compound meter, like 12/8.

[Olimar12345]

^100% agree, just listen to that drum set-definitely not swing. I'd probably use 12/16, but that's just me.

[Dekkadeci]

What key and time signature is this in?

I have a feeling it's in swing 4/4 and E flat major but I'm not so sure.

I agree it's in compound quadruple meter (I'd probably end up using 12/8 time), but it swings pretty rapidly between a Bb tonic and a C tonic (leaning towards Bb major-like, C minor-like, F-minor-solo-on-dominant-like, and C-double-harmonic-like). I suspect you may need to rapidly change key signatures or pick a base key signature based on the ones I suggested, then put on a lot of accidentals.

[WaluigiTime64]

Is the first section in 3/4, 6/8 or 12/8? I don't actually know the difference (between 6/8 and 12/8), so an explanation would be nice!

[Altissimo]

The difference between 6/8 and 12/8 is akin to the difference between 2/4 and 4/4 - whether the piece relies on 2-beat or 4-beat units.

[WaluigiTime64]

Using that logic (to an extent), is the first section in 6/8?

[Altissimo]

It's a little hard to tell, I'm not quite sure (sorry!) I only stopped in to mention the 6/8 12/8 thing because you asked.

[mikey]

why not just count the whole thing in 4/4

[Dudeman]

I'd say 12/8, personally. I don't think two-beat phrases really work here.

[Olimar12345]

^6/8 would actually work pretty great here. There are two, 2-beat phrases per chord-change, so you could have them one-per-bar without having really long, compound 12/8 measures.

why not just count the whole thing in 4/4

You're joking, right? xD

[WaluigiTime64]

Judging by the first 4 measures, 6/8 is probably the most suitable for this.

[Olimar12345]

whoa, you've turned around the beat there. Half the note values and condense every two measures into one measure.

[WaluigiTime64]

Hmm... Kinda looks off though.
Also I'm going to have to half the note values for the entire arrangement...

[Olimar12345]

That looks right to me! That's how I'd do it! :D

[WaluigiTime64]

Just a quick comparison here.

I've been taught that 6/8 time goes: 1 + + 2 + +
Compared to 3/4, which goes: 1 + 2 + 3 +

The first image (what I had originally), matches the bassline to the beat of 6/8. The second image (what you're telling me) doesn't match, so I never even considered it when arranging.