everyone, an easy way is this.
Start recording your demo using /record NameOfDemo and stop using /stoprecord when done.
then open the console and type devmap mp_rust and wait for it to load. Once loaded open console again and type /killserver. This will take you to the main menu. When this happens open console again and type demo NameOfDemo and your demo will open. It will be glitched at the start but timescale out using /timescale and a relevant number like 2 or 4. this will speed up the demo. Before you get to your clip(if thats what you record for) use /timescale 0.25 and record with your fraps. when in sony vegas hold Ctrl and drag the end of the clip all the way right. Right clickthe audio and go to properties and click lock to stretch. Render and you are done! If any problems occur i may make a video on it