man
output has a lot of hidden backspace characters. All the extra S
and BS
characters you see are special characters. The following command will clear those:
man ffmpeg | col -b > man_ffmpeg.txt
Now you get crystal clear plain text output.
Source:
man man
...
To get a plain text version of a man page, without backspaces and underscores, try
# man foo | col -b > foo.mantxt
Edit: Minor clarification