What is best way to purchase music to use in a video?

Do you have any idea who owns the rights?

Its classical so there are several different orchestras performing the song.

The legal work and cost of a licensing a published song isn't going to be worth your trouble. Your best bet is to find an unsigned artist willing to let you use the music for cheap or free. That, or use royalty-free music.

Is it a specific song you're interested in or just a genre of music?

Idk but I tried uploading a video I made for my kids' birthday and Facebook and YouTube shut it down before it could even be played. Had to upload it to Vimeo in order to avoid copyright issues.

Don't see how so many people can put up lyric videos or other shite given the filters on YouTube. I even changed the pitch up/down a half step and it recognized the song.

You can use it SO LONG as you don't profit off of it.

I was going to suggest, if the music itself (not the performance) was public domain, and it were a relatively simple piece, you could find someone to record a performance of it for you. Or use software like Cubase to create a version of it.

I'm getting into filmmaking and I'm planning on creating my own music this way. It helps to have a background in music or know someone who does.

Best bet would be to find someone unknown or get a musician to record public domain music. There's a reason the biggest expense of a movie's budget is for the score.

Try to see if you can find one under an applicable Creative Commons license. See creativecommons.org.

What is the song?

I've seen some budgets for Hollywood films where the total budget was $100M and the budget for music was $50M or more. Composer + orchestra + rights for well-known songs and it can add up.

Microsoft paid $3M for "Start Me Up" for a commercial.