Meakinsl, Here's something you can do if you would like the music playing in the background while the video audio will be what you hear the loudest. I do this and I think it sounds better than just stopping the music and then starting the music again.
Click on the music track in the timeline then press the "V" key.
There should be a bold blue line appear.
Go to the spot where the video starts, double click on the blue line just before the video, a little blue box should be on the blue line now, double click to the right of the blue box that you just created and another blue box should pop up, so now you should have two blue boxes next to each other.
Click and hold the left mouse button on the second blue box and slide it down until you are close to the bottom of the music track.
Now go to the end of the video track, double click on the blue line, a box will pop up, double click next to the the box you just made. You should have two blue boxes next to each other.
Click and hold the left mouse button on the second blue box you just created and move back up to get the volume level as it originally was before you lowered it.
That's pretty much it, like I said you will have the music still playnig in the background during the video and the video sound will be the loudest of what you hear and then your music sound will go back up to where it originally was.
Hope this helps.

A slight improvement to that workflow is to add the four dots first, then drag down the line between the middle two dots. This leaves the volume afterwards untouched so it's still the same as before, without having to move it back up to that spot.

Good tip! I never thought of doing it that way.

Thanks for replies and apologies taken so long to reply (work been a bit of a nightmare), definitiely learnt a trick there and will use that in a couple of places but one piece I would like just the video adudio and doing it that way means I lose a bit of the song so would be good to know how to split the track if there is a way.

Many thanks,

Lawrence

As Chienworks said: Click on the song on the timeline where you want to split it and press the S key.

OR .. you can fade the music out to nothing. Add a NEW audio track and put another copy of the song on that new track. You can re-start the song after the video, or you can start it earlier (but have the volume down to zero) and slide it back and forth until the SONG ENDS when your PROJECT ENDS.

When the video ends you adjust the volume on the new song from zero up to a 'normal' level, but now the song is timed to end exactly when the project ends.

"doing it that way means I lose a bit of the song"

That's because Vegas applies automatic fades at audio split points to eliminate loud clicks and pops at the split points.

You can certainly turn off autofades in Preferences, turn off Quantize to frames, hit "U" to ungroup the audio from video (so you don't split the video at a non-frame boundary), zoom in to the timeline to the sample level, and manually make your splits precisely at zero amplitude crossings if you wish.