I've got all of my demos from my run and want to record them for my yt. I've done this with tf2 demos, using lawena. I'm 99% sure you can't use lawena with Portal. What's a good alternative for doing so? And does it have a queue option? (So I can add up all of my demos and record them)
use the command startmovie and run the demos using playdemo
This is a helpful guide i used when making a segmented run https://wiki.sourceruns.org/wiki/Source_Video_Creation
The only way to do it clean is to do what hat said. The clodo strat is that you record your game with OBS/XSplit/Mishira/Bandicam Playing many demos at a time isn't something I would recommend.
Startong today, runs that require video proof (top 25) and runs beyond that where video is the only form of proof, now require audio, as recording audio for only the game is now a native OBS feature.