f=webm

acodec=libopus
ar=48000
ab=128k

vcodec=libvpx-vp9
vb=2M
g=120
bf=2
threads=0
rc_lookahead=16
quality=good
speed=3
vprofile=0
qmax=51
qmin=4
slices=4
tile-columns=6
frame-parallel=1
lag-in-frames=25
row-mt=1
auto-alt-ref=0
mlt_image_format=rgba
pix_fmt=yuva420p

meta.preset.name=alpha/WebM VP9 with alpha channel
meta.preset.extension=webm
meta.preset.note=VP9 video with Opus audio in Matroska container: "Don't be evil"
