What you doing? I have used such a program in doze years ago while I
was sailing. Used it for weather fax on 10 meters. The NL/CR character
in the broadcast starts the scan on a new line making a partial picture
if you start in the middle of a broadcast.

Most such programs just listen and print as the start of the line comes in.

downloaded and started qsstv using terminal. just type in qsstv at the
prompt to start. adjust the volume using the volume scale and test with
a transmisson received. looks very straight forward.