I'm not sure, maybe the jumping community has found out another way to do this they did, but afaik the only way is to have a separate client in the game recording a demo, and then smooth from that.

many people in the jump community use HLAE to export the camera (and the map with crafty) to an external program such as cinema 4d where the demo smoothing is performed. the camera is then imported back into HLAE and recorded.

this allows you to smooth from an STV demo or even to view yourself in a POV smooth.

What wonderland said:
https://youtu.be/a28waa30-bw

Wow! Thanks guys! I will definitely look into that.

Just one more question, when I am using Lawena Recording tool for jumps, my viewmodel jitters/moves back and forth. Is there a certain command to fix that? I've tried cl_smoothtime and cl_autoreload, but is there anything else?

I always record POVs from stv demos, this completely removes any jitter for me. You can also try to slow down the demo playback speed, that tends to help a bit as well.

Keep your viewmodel from bugging out: cl_autoreload 1 or 0, enter the opposite of whatever you usually use
Erase rocket explosion marks (so you can't see the explosions from the 10 times you tried the jump before you got it): r_decals 0 mp_decals 0 r_drawdecals 0 (courtesy of a youtube comment by obsidiian)

What about damage indicators (the red bars)?

what about them?
you need to use POV to get damage indicators, which is one reason to use POV instead of STV.
its also harder to TAS or cut a POV run so thats another reason to use POV

if you mean how to get them with lawena idk i dont use the program, if it doesnt have them then load a custom hud in it I guess.
you also can't use lawena in HLAE afaik

Ah. Thank you! I was planning to use lawena for like just plain POV stuff, some surfing vids, frag vids, etc. and then use HLAE for smoothing.

So, with HLAE, does that allow for smoothing without the particle and camera effects of jumps? That's the biggest setback to when one simply smooths from a POV demo.

Yes