https://bugs.kde.org/show_bug.cgi?id=516966
Bug ID: 516966
Summary: Rendering video with alpha channel renders no alpha
channel
Classification: Applications
Product: kdenlive
Version First 25.12.2
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: Rendering & Export
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
Rendering a video with alpha channel does not work. The resulting video does
not contain an alpha channel – the pix_fmt is always yuva420p, no matter which
of the “Video with Alpha” presets I choose. Verified with ffprobe:
$ ffprobe ende01.webm
ffprobe version 7.1.3 Copyright (c) 2007-2025 the FFmpeg developers
built with gcc 14 (Debian 14.2.0-19)
configuration: --disable-decoder=amrnb --disable-gnutls --disable-liblensfun
--disable-libopencv --disable-podpages --disable-sndio --disable-stripping
--disable-omx --enable-avfilter --enable-chromaprint --enable-frei0r
--enable-gcry
pt --enable-gpl --enable-ladspa --enable-libaom --enable-libaribb24
--enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca
--enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libdavs2
--enable-libdc1394 --enable
-libdrm --enable-libdvdnav --enable-libdvdread --enable-libfdk-aac
--enable-libflite --enable-libfontconfig --enable-libfreetype
--enable-libfribidi --enable-libgme --enable-libgsm --enable-libharfbuzz
--enable-libiec61883 --enable-libi
lbc --enable-libjack --enable-libjxl --enable-libklvanc --enable-libkvazaar
--enable-libmp3lame --enable-libmysofa --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg
--enable-libopenmpt --ena
ble-libopus --enable-libplacebo --enable-libpulse --enable-librabbitmq
--enable-librist --enable-librsvg --enable-librubberband --enable-libshine
--enable-libsmbclient --enable-libsnappy --enable-libsoxr --enable-libspeex
--enable-libsr
t --enable-libsvtav1 --enable-libtesseract --enable-libtheora
--enable-libtwolame --enable-libvidstab --enable-libvmaf
--enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp
--enable-libwebp --enable-libx264 --enabl
e-libx265 --enable-libxavs2 --enable-libxml2 --enable-libxvid --enable-libzimg
--enable-libzmq --enable-libzvbi --enable-lv2 --enable-nonfree --enable-openal
--enable-opencl --enable-opengl --enable-openssl --enable-postproc --enable-pt
hreads --enable-shared --enable-version3 --incdir=/usr/include/x86_64-linux-gnu
--libdir=/usr/lib/x86_64-linux-gnu --prefix=/usr --toolchain=hardened
--enable-vaapi --enable-libvpl --cc=x86_64-linux-gnu-gcc
--cxx=x86_64-linux-gnu-g++ --
disable-altivec --shlibdir=/usr/lib/x86_64-linux-gnu
libavutil 59. 39.100 / 59. 39.100
libavcodec 61. 19.101 / 61. 19.101
libavformat 61. 7.100 / 61. 7.100
libavdevice 61. 3.100 / 61. 3.100
libavfilter 10. 4.100 / 10. 4.100
libswscale 8. 3.100 / 8. 3.100
libswresample 5. 3.100 / 5. 3.100
libpostproc 58. 3.100 / 58. 3.100
Input #0, matroska,webm, from 'ende01.webm':
Metadata:
ENCODER : Lavf61.7.100
Duration: 00:00:16.89, start: 0.000000, bitrate: 2364 kb/s
Stream #0:0: Video: vp9 (Profile 0), yuv420p(tv, bt709), 1920x1080, SAR 1:1
DAR 16:9, 29.97 fps, 29.97 tbr, 1k tbn
Metadata:
alpha_mode : 1
DURATION : 00:00:16.886000000
Stream #0:1: Audio: vorbis, 48000 Hz, stereo, fltp
Metadata:
DURATION : 00:00:16.887000000
Preview Rendering has the same problem. Once i pre-render a timeline, its alpha
channel is gone.
STEPS TO REPRODUCE
1. create something on with alpha channel
2. export using one of the "Video with Alpha" presets
OBSERVED RESULT
resulting video has no alpha channel
EXPECTED RESULT
resulting video should have alpha channel
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Linux 6.12.63+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian
6.12.63-1 (2025-12-30) x86_64 GNU/Linux
KDE Plasma Version: plasmashell 6.3.6
KDE Frameworks Version: 6.3.6
Qt Version: 6.3.6
ADDITIONAL INFORMATION
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