Sometimes you just want a general source for testing a new encoding config and don’t want to have to specify a source. For this the smptebars filter is very useful.
Here is how to push it out as an example to Wowza:
ffmpeg -re -f lavfi -i smptebars -s 640×360 -g 25 -c:v libx264 -b:v 500k -an -f flv rtmp://wowserver.com/live/myStream
or for HD
ffmpeg -re -f lavfi -i smptehdbars -s 1920×1080 -g 25 -c:v libx264 -b:v 4500k -an -f flv rtmp://wowserver.com/live/myStream