Teeworlds change the demo render fps. (DDNet)

Tap f1.
Set cl_video_recorder_fps to your desired number.
Render it.

P.S.
You can set the fps from 0 to 1000.
If you want to change it you'll have to modify the source code.

go to ddnet/src/engine/shared/config_variables.h file and chage
in this line
MACRO_CONFIG_INT(ClVideoRecorderFPS, cl_video_recorder_fps, 60, 1, 1000, CFGFLAG_SAVE | CFGFLAG_CLIENT, "At which FPS the videorecorder should record demos.")
the 1000 to your desired max fps integer number.