Software Defined Radio

I am new to sdr. Currently I have an rlt-sdr dongle running rtl_fm piped to ffmpeg. I’d like to switch to something that I can change the frequency without shutting it down and can be run as a daemon on linux, ie no tui or gui. I am having difficulty finding anything currently available.

Is there anything out there or is my only choice to modify rtl_fm to do what I am wanting?