All you need to do is add the
--rate switch after
vlc and specify the value you want or have tested in
vlc previously; for example, from the command line I could play a file with
vlc --rate 3 myfile.mp4
vlc --rate 3 (substitute 3 for the value you want) is the key part of what you need for your launcher.
More command-line options for
vlc are available by entering in the terminal
vlc -h, or
vlc -H for exhaustive help.
I don't know which desktop you are on, but on Xfce I create a very simple vlc mp4 launcher
.desktop file in
~/.local/share/applications in this format (and make it executable):
Exec=/usr/bin/vlc --rate 3 %U
Then simply go to your file browser and right click an mp4 file, select this launcher, and check the box to make sure that all mp4s are opened with this
.desktop application from now on. Now just clicking the video file will make it play using your custom parameters, but will leave unaffected any other video file that
This is the quickest way to associate your launcher with the filetype, but to do it manually you would edit
~/.local/share/applications/mimeapps.list and add the name of your launcher. As an example, you would add
video/mp4=vlcmp4.desktop to the [Default Applications] section and the [Added Associations list] section should have
More information on
.desktop files and launchers is here at the Ubuntu help pages.