ffmpeg man page is WRONG and damaged my original source file

from man ffmpeg

       -pass n
           Select the pass number (1 or 2). It is used to do two-pass video encoding. The statistics of
           the video are recorded in the first pass into a log file (see also the option -passlogfile),
           and in the second pass that log file is used to generate the video at the exact requested
           bitrate.  On pass 1, you may just deactivate audio and set output to null, examples for
           Windows and Unix:

                   ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y NUL
                   ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y /dev/null

       -passlogfile prefix
           Set two-pass log file name prefix to prefix, the default file name prefix is ``ffmpeg2pass''.
           The complete file name will be PREFIX-N.log, where N is a number specific to the output
           stream.