what would I need to do in Audacity to make this beat music loop seamlessly without noticeable breaks where you can tell they weren’t joined properly?
Start at 1990 samples.
End at 1,304,676 samples.
Don’t encode as MP3, AAC or WMA. Export the selection in a lossless format (such as WAV or FLAC) or if you need a compressed format use OGG.
how do I tell it to start and end at those samples? I cannot figure it out
Open the song in Audacity. See the time windows at the bottom of the frame? Use the pulldowns to change the measurement to samples. Use the published numbers from Steve, above.
If you have View > Show Clipping turned on, the blue waves will turn into a sea of red overload bars. You can either turn Show Clipping off, or you can Effect > Amplify to -1dB. That will make it easier to see and nobody will miss the volume change.
Then Transport > Loop Play or the shortcut Shift-Spacebar. That will loop until the earth ends.
File > Export Selected to play the loop somewhere else.
Again, DO NOT use MP3 or any of the compressed formats. They all mess with the timing and will throw the loop off.
If MP3 is required, then you have to use cut and paste to create a finished loop show for the whole time it’s needed and then File > Export that.
See here: Audacity Manual
Or use Effect > Repeat on the selection.