This one does up to 50 arguments you may want to extend the number of arguments by changing the for-loop. just download and unzip the source code archive and executing the launcher script inside. When you have finished downloading, double-click the 'ffmpeg64bitosx.pkg' in your Downloads folder. In the 64-bit FFmpeg section, left-click the link 'ffmpeg64bitosx.pkg' and save the file anywhere on your computer. If you see unrecognized command or something other than a list, go back to the previous task and try it again. Left-click this link, do not right-click. To check out the available vfw drivers, you can use this on the Avanti command line -new -r 29.97 -f vfwcap -i list If you run this you should get a list of available vfw drivers (if any). You should see a list of codecs available to FFMPEG once you hit Enter.

Because the script has a lot of repetition, I'll include here a script which outputs the DTrace script which works well. Videomass is a cross-platform GUI for FFmpeg and youtube-dl. As described in the Linux example, 'you must activate the right video source and channel before launching ffmpeg'.

Based on the discussion I had with Joey Hagedorn in the comments elsewhere on this question, the script that comes with 10.6 can be improved to work with a reasonable number of arguments (50+).

Ffmpeg gui source code