What you want to do is turn the bits of the demo you need into video files.
All you need to do is replay the demo, bring down the console and type in cl_capturevideo 1 and the game will start recording that part of the demo to a video file. cl_capturevideo 0 will stop it recording.
I also have some tip for video recording: if your demo is too long you don't need to watch the whole, you can fastforward with the "slowmo" command. You need to write after that how fast you want the demo to play back, for example if you want it to be 5 times faster you type "slowmo 5" to the console. The normal speed is slowmo 1.