avfilter/vf_histogram: fix segfault in parade waveform mode for subsampled formats

Signed-off-by: Marton Balint <cus@passwd.hu>
avfilter/vf_histogram: add mirrored waveform mode

Added parameter to mirror the waveform (high values are shown on top in column mode)

Signed-off-by: Marton Balint <cus@passwd.hu>
avcodec: add av_codec_get_max_lowres()

Reviewed-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>