title: Matte
media types:
Video
description: Replace the alpha channel of track A with the luma channel from track B.
version: 1
creator: Maksym Veremeyenko
copyright: Meltytech, LLC
license: LGPLv2.1
Please note that the transition automatically detects if the frame
from track B has scaled or non-scaled luma. The frame property
"full_range" should indicate it.
If you need to prepare fill and key (matte) files, you can use melt or
ffmpeg to extract alpha channel from existing video:
melt sg_gm_2013_clip_title.avi -attach frei0r.alpha0ps 0=0.21 -consumer
avformat:sg_gm_2013_clip_title.matte_scaled.mp4 crf=10 preset=placebo an=1
ffmpeg -i sg_gm_2013_clip_title.avi -vf "alphaextract" -pix_fmt
yuv422p -preset placebo -crf 10 -y sg_gm_2013_clip_title.matte_scaled.mp4
Because the example above provides a scaled luma output, the transition
performs scaling from [16,235] -> [0, 255].
It is possible to create unscaled (full) range:
melt sg_gm_2013_clip_title.avi -attach frei0r.alpha0ps 0=0.21 -consumer
avformat:sg_gm_2013_clip_title.matte_full.mp4 crf=10 preset=placebo an=1
mlt_image_format=rgba pix_fmt=yuvj422p
ffmpeg -i sg_gm_2013_clip_title.avi -vf "alphaextract" -pix_fmt
yuvj422p -preset placebo -crf 10 -y sg_gm_2013_clip_title.matte_full.mp4
The fill can be converted from rgba to yuv422:
melt sg_gm_2013_clip_title.avi -consumer avformat:sg_gm_2013_clip_title.fill.mp4
crf=10 preset=placebo an=1
ffmpeg -i sg_gm_2013_clip_title.avi -pix_fmt yuv422p -preset placebo -crf 10 -y
sg_gm_2013_clip_title.fill.mp4
Putting it all together:
melt sg_gm_2013_clip_title.matte_full.mp4 -track noise: -track
sg_gm_2013_clip_title.fill.mp4 -transition matte a_track=2
b_track=0 -transition composite a_track=1 b_track=2
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