Is there a way to capture my voice when I press F1 in game to capture footage?
Yes it is indeed possible, but not with the build-in recording tool. You would require a screencasting software that records your video output as well as your microphone input.
Here's a list of well-known screencasting software
GTA doesn't save the images your graphic card generates. It only saves something like a screen-play or a blueprint of the scene you're recording.
It saves movement, orientation and interactions of objects such as your character, NPCs, projectiles and more. For example when you record and fire a gun GTA will save your action (shoot) as well as your current coordinates and orientation (where you are & which direction you shoot). This way of recording saves a lot of resources and makes recording way less hardware-hungry.
Later when you watch this recorded movie it sets up the game the way it was when you were recording and then just moves all the recorded objects the way you recorded them.
I haven't found any resource that displays how it works but i looked at multiple documents and i saw that its really hardware efficient. I'm pretty sure that GTA uses this technique of recording even tho I don't have articles or files that approve this.