Update print mode output header line format to be more consistent with
other log output of FFmpeg. The printf-modifiers have been inspired by
the showinfo filter.
Signed-off-by: Tobias Rapp <t.rapp@noa-archive.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>