adpcm: Fix trellis encoding of IMA QT

This was broken in 095be4fb - samples+ch (for the previous
non-planar case) equals &samples_p[ch][0]. The confusion
probably stemmed from the IMA WAV case where it originally
was &samples[avctx->channels + ch], which was correctly
changed into &samples_p[ch][1].

Fixes part of Ticket3701

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
fate: enable adpcm-ima_qt-trellis

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
adpcm: Write the proper predictor in trellis mode in IMA QT

The actual predictor value, set by the trellis code, never
was written back into the variable that was written into
the block header. This was accidentally removed in b304244b.

This significantly improves the audio quality of the trellis
case, which was plain broken since b304244b.

Encoding IMA QT with trellis still actually gives a slightly
worse quality than without trellis, since the trellis encoder
doesn't use the exact same way of rounding as in
adpcm_ima_qt_compress_sample and adpcm_ima_qt_expand_nibble.

Fixes part of Ticket3701

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/libm: Replace macro based fminf() by function

This avoids issues when the FFMIN parameter evaluation has side effects

Reviewed-by: Clément Bœsch <u@pkh.me>
Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/avf_showcqt: avoid using fminf()

The loop with fminf() changes from 18093856 to 17403218 dezicycles (gcc 4.6.3, sandybridge i7)

Reviewed-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>