As mentioned in email: > From what I can tell, codecalpha is not a native VP8/VP9 decoder but a wrapper > that adds alpha blending support. Which is how it takes a colourless video and > applies the accent colour to it. This is required to implement the Matroska > 'AlphaMode' element used in the video files, which is implemented in GStreamer > by only one plugin offering the 'codec-alpha' capability.
The main difficulty in dealing with these videos is that most VP9 decoders don't understand the alpha channel and will render them incorrectly. You'll usually only see them rendered correctly in web browsers, or if you have the "bad" gstreamer plugins installed then you can use: gst-launch-1.0 filesrc location=INFILE.webm ! matroskademux ! decodebin ! glimagesink But I could not figure out how to get GStreamer to transcode, and eventually gave up on GStreamer. FFmpeg is usually more reliable and easier to work with, but it too doesn't understand the alpha channel by default: ffplay INFILE.webm But finally I figured out how to interpret the alpha channel and convert each file into greyscale (or any colour you choose): ffmpeg -c:v libvpx-vp9 -i INFILE.webm -vf alphaextract,colorize=hue=0:saturation=0:lightness=1:mix=0.5 OUTFILE.webm Please find attached some new videos that are white on grey. ** Attachment added: "greyscale-videos.zip" https://bugs.launchpad.net/ubuntu/+source/gtk4/+bug/2077117/+attachment/5813855/+files/greyscale-videos.zip -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gtk4 in Ubuntu. https://bugs.launchpad.net/bugs/2077117 Title: settings - mouse&touchpad - scroll direction images empty Status in gnome-control-center package in Ubuntu: New Status in gtk4 package in Ubuntu: In Progress Bug description: Settings - mouse&touchpad - scroll direction images empty see attached screenshot ProblemType: Bug DistroRelease: Ubuntu 24.10 Package: gnome-control-center 1:47~beta-2ubuntu1 ProcVersionSignature: Ubuntu 6.8.0-31.31-generic 6.8.1 Uname: Linux 6.8.0-31-generic x86_64 ApportVersion: 2.30.0-0ubuntu1 Architecture: amd64 CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Thu Aug 15 20:39:33 2024 InstallationDate: Installed on 2024-08-10 (5 days ago) InstallationMedia: Ubuntu 24.10 "Oracular Oriole" - Daily amd64 (20240810) ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no user) SHELL=/bin/bash TERM=xterm-256color XDG_RUNTIME_DIR=<set> SourcePackage: gnome-control-center UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/2077117/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
