opt_input_file(). More consistent and more clear, as "filename" can be
easily confused with the global "input_filename".
Originally committed as revision 22045 to svn://svn.ffmpeg.org/ffmpeg/trunk
This is a simplified / cleaned-up version of the SourceForge program:
http://sourceforge.net/projects/ffprobe/
Syntax / features may be different, in particular the options
-show_packets and -show_frames are not yet supported in this version.
Originally committed as revision 21936 to svn://svn.ffmpeg.org/ffmpeg/trunk