了解MLT融混合机混合亮度（淡出）时间？(Understanding MLT melt mixer

相关谅解/控制MLT融化幻灯片？，我想了解如何融化的亮度混频器的工作，尤其是在短期（小帧数）的持续时间范围内。

举例来说，如果我用这样的规格tmppics/pic_01.jpg length=6 -mix 2 -mixer luma我本来期望pic_01的淡入淡出的2帧，然后2帧全pic_01，然后淡出的2帧再次-然而，我已经都经历的结果是这样的，和那些没有。

为了澄清这一点，我已经开发了一个bash脚本，它使用ImageMagick的convert生成测试图像，然后melt使“幻灯”与淡出这些图像， ffmpeg将其转换成.gif动画，然后ImageMagick的convert和montage以获得视频.gif注意的薄膜条带（子画面的片）（Ubuntu的18.04，熔融6.6.0，FFMPEG版本3.4.4-0ubuntu0.18.04.1，ImageMagick的6.9.7-4 Q16 x86_64的20170114）。

这里是bash脚本， melt-test-strip.sh ：

#!/usr/bin/env bash

FRAMERATE=25
echo "
description=DV PAL
frame_rate_num=$FRAMERATE
frame_rate_den=1
width=720
height=576
progressive=0
sample_aspect_num=59
sample_aspect_den=54
display_aspect_num=4
display_aspect_den=3
colorspace=601
" > my-melt.profile

mkdir tmppics
convert -background lightblue -fill blue -size 3840x2160  -pointsize 200  -gravity center label:"Test A" tmppics/pic_01.jpg
convert -background lightblue -fill blue -size 2160x3840  -pointsize 200  -gravity center label:"Test B" tmppics/pic_02.jpg

if [ -z "$IMGDURATIONF" ]; then
  IMGDURATIONF=6 # picture duration, frames
fi
if [ -z "$FADEDURATIONF" ]; then
  FADEDURATIONF=2 # single-end fade duration, frames
fi

melt -verbose -profile ./my-melt.profile \
tmppics/pic_01.jpg length=$IMGDURATIONF \
tmppics/pic_02.jpg length=$IMGDURATIONF -mix $FADEDURATIONF -mixer luma \
colour:black length=$IMGDURATIONF -mix $FADEDURATIONF -mixer luma \
-consumer avformat:meltout.mp4 vcodec=libx264 an=1

# auxiliary: just for creating sprite sheet/film strip:
melt -verbose -profile ./my-melt.profile tmppics/pic_01.jpg length=$IMGDURATIONF -consumer avformat:meltout-01.mp4 vcodec=libx264 an=1
melt -verbose -profile ./my-melt.profile tmppics/pic_02.jpg length=$IMGDURATIONF -consumer avformat:meltout-02.mp4 vcodec=libx264 an=1
melt -verbose -profile ./my-melt.profile colour:black length=$IMGDURATIONF -consumer avformat:meltout-b.mp4 vcodec=libx264 an=1

# convert to gif to obtain sprite sheet/film strip from:
ffmpeg \
  -i meltout.mp4 \
  -r 25 \
  -vf scale=256:-1 \
  -y meltout.gif


# auxiliary: just for creating sprite sheet/film strip:
ffmpeg -i meltout-01.mp4 -r $FRAMERATE -vf scale=256:-1 -y meltout-01.gif
ffmpeg -i meltout-02.mp4 -r $FRAMERATE -vf scale=256:-1 -y meltout-02.gif
ffmpeg -i meltout-b.mp4 -r $FRAMERATE -vf scale=256:-1 -y meltout-b.gif

convert meltout.gif -coalesce meltoutc.gif
convert meltout-01.gif -coalesce meltoutc-01.gif
convert meltout-02.gif -coalesce meltoutc-02.gif
convert meltout-b.gif -coalesce meltoutc-b.gif

FRAMETHICK=5
#~ montage temp.gif -tile x1 -geometry '1x1+0+0<' -border 5 -bordercolor "rgb(200, 200, 200)" -label 'Image' -quality 100 meltout.png
# "%p   index of image in current image list" is "t=> index of current image (s) in list" in fx:
montage  -label 'Frame %[fx:t+1]/%n' meltoutc.gif -tile x1 -geometry '1x1+0+0<' -frame $FRAMETHICK -bordercolor "rgb(200, 200, 200)"  -quality 100 meltout.png

# here from the .gif - otherwise for replicating images: montage in.jpg +clone +clone +clone -tile x4 -geometry +0+0 out.jpg
montage  -label 'Frame %[fx:t+1]/%n' meltoutc-01.gif -tile x1 -geometry '1x1+0+0<' -frame $FRAMETHICK -bordercolor "rgb(200, 200, 200)"  -quality 100 meltout-01.png
montage  -label 'Frame %[fx:t+1]/%n' meltoutc-02.gif -tile x1 -geometry '1x1+0+0<' -frame $FRAMETHICK -bordercolor "rgb(200, 200, 200)"  -quality 100 meltout-02.png
montage  -label 'Frame %[fx:t+1]/%n' meltoutc-b.gif -tile x1 -geometry '1x1+0+0<' -frame $FRAMETHICK -bordercolor "rgb(200, 200, 200)"  -quality 100 meltout-b.png

# for offsetting:
# (gif) frame width/height
fw=$(convert meltoutc-01.gif[0] -format "%w" info:)
fh=$(convert meltoutc-01.gif[0] -format "%w" info:)
# strip width/height
sw=$(convert meltout.png -format "%w" info:)
sh=$(convert meltout.png -format "%h" info:)

echo fw $fw fh $fh sw $sw sh $sh

convert -size $(( (IMGDURATIONF-FADEDURATIONF)*(fw+2*FRAMETHICK) ))x$sh xc:white meltout-02.png +append meltout-02B.png
# IMGDURATIONF-FADEDURATIONF to get to the start of second clip; +IMGDURATIONF from there to get to end of second clip, and -FADEDURATIONF from there to get to start of third clip
convert -size $(( (IMGDURATIONF-FADEDURATIONF+IMGDURATIONF-FADEDURATIONF)*(fw+2*FRAMETHICK) ))x$sh xc:white meltout-b.png +append meltout-bB.png

montage  -geometry '+0+0' meltout.png meltout-01.png meltout-02B.png meltout-bB.png -tile 1x meltout-all.png

eog meltout-all.png

所以，如果你拨打bash melt-test-strip.sh ，你会得到默认，IMGDURATIONF = 6和FADEDURATIONF = 2，对于其输出是这个（点击查看原图）：