to directly answer your question
demo_resume
is probably the command you're looking for
Usually i press resume on the demo like 20 some seconds or so before i actually want to start recording, hit a bind to startmovie movienamehere and then hit a bind to endmovie
host_framerate 60 // for 60fps video, for example
bind [ startmovie lol
bind ] endmovie
this creates a bunch of .tga images per frame and a .wav file in your tf folder
i typically move all these to their own folder before working with them
then i use virtualdub to quickly spit out an .avi video synced to the sound
you just need to open up frame 0 in virtual dub and it'll handle parsing the rest, then choose audio from other source, and then set the framerate so that audio and video length match, it's usually very accurate
then i just edit out the frames where the demoui is showing with lightworks or something
there's decent free software out there for video editing, such as the aforementioned lightworks
you can always ''aquire'' the heavy duty software if you really feel you need it or something
as for quality, i assume you mean when youtube destroys your video after you upload it, even if it looks real nice on your computer
this is in fact, youtubes fault, but if your video is at 1440p or 4k, you get higher and higher allowed bitrates at each level, so you could record like usual, and if your computer can take it, render it out to 1440p or 4k at some like 50+ mbps or even higher depending on framerate and it should theoretically look nicer at the lower quality choices
edit: you mentioned that you're on mac os i think in your other thread, i'm sure there's alternative software to things like virtualdub that can accept .tga files as input. i recall something out there called filmora or soemthing that could do it