Did alot of digging into my problem but I can't believe this is the legit reason why my audio will only be captured on Relive if I use my monitors Audio only and will fail If i use my 3.5mm Headphones plugged into the back of my motherboard?
"I have figured this out for myself..
So you have to use AMD High definition audio device as your default playback device.
Go to playback devices in windows and then set AMD AMD High definition audio device as default.
That works for me and also records microphone. BUT comes with a big flaw: Your speaker must be your monitor and that isn't nice at all. I don't want to play games with my monitor being my speaker. And the sound quality isn't good either.
I hope this gets fixed so that you can use your headphones as audio capture device"
Relive audio capture - Only Microphones are selectable for Audio Capture Device.
Here is my current sound options
And also when I do record (even though no game audio but I can record my voice) when I replay the video on either windows own player and even VLC player there seems to be an issue moving the time slider which crash's the video aswell.
Similar to this issue linked below
Oddly or should I say worryingly I do believe my 3440x1440 is the same model as 2 of the people showing this exact same issue also.
Any knowledge on getting either or both of these issues fix would be greatly, greatly appreciated.
Many thanks in advance,
I would just like to second this. I have been searching for quite a while now for an answer to this problem. Seems like there needs to be a way to select the audio output source as well that will be captured in ReLive settings. Other than this issue, Relive is awesome. The instant replay feature is incredible! Now if only instant replays of me getting wrecked in games could have audio to go along with them 
