Add -?, -help, and --help as alternative options to get help.
Originally committed as revision 20906 to svn://svn.ffmpeg.org/ffmpeg/trunk
Implement a -filters option, listing all the available libavfilterfilters.Currently filters are not registered, so the option will show none.
Originally committed as revision 20807 to svn://svn.ffmpeg.org/ffmpeg/trunk
Factorize common commandline options definition.
Originally committed as revision 20664 to svn://svn.ffmpeg.org/ffmpeg/trunk