title: How do I suppress `ffmpeg`'s "Filter ... has an unconnected output" error?
body: <p>If I write something like <code>ffmpeg -i INPUT.mp4 -filter_complex '[0:v]trim=end=1[test],[0:v]trim=end=2[out]' -map '[out]' OUT.mp4</code>, I get <code>Filter trim has an unconnected output</code>.  This is annoying when debugging my complex filter, because I want to build it up in pieces and not have to worry about useless filters.  How do I suppress this error message while developing?</p>