ffmpeg: use a rational for -aspect option.
ffmpeg: print frame decoding error statistic

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  ffmpeg: use a rational for -aspect option.

Merged-by: Michael Niedermayer <michaelni@gmx.at>