1. Download MX player(for video) and playmusic/Spotify or any app for music/MP3 playback.
2. Open MX player
3. Then go to local Player settings> Player> Playback section> and uncheck play alone option.
4. Go to equaiizer settings (of max player) and make everything( all frequencies) to 0.
5. Now you can play any video on MX player with zero volume while simultaneously playing music using another MP3 player app at full volume.

Note! If you have a samsung device you can do it by samsung’s built in soundassistant settings.

https://www.quora.com/How-do-I-play-a-video-in-Android-with-zero-volume-while-simultaneously-playing-music-using-another-MP3-player-app-at-full-volume

If you have a headless machine (ie: no monitor plugged into it) you’ll need to either install a “HDMI headless dummy connector” or you can install a Video Dummy Package:

sudo apt-get install xserver-xorg-video-dummy

Then add a configuration file for it:

sudo vi /usr/share/X11/xorg.conf.d/xorg.conf

and paste this (adjusting your desired resolution)

Section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy"
EndSection

Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync 31.5-48.5
    VertRefresh 50-70
EndSection

Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
    Depth 24
    Modes "1920x1080"
    EndSubSection
EndSection

Then reboot the machine and voilá

Source: Ubuntu 20.04 shows a black screen when connecting through Teamviewer, but I still have ssh access. How can I get back the desktop? – Ask Ubuntu

Both LEDs and fluorescent lights require a buffer between the lamp and the power supply. While fluorescents use ballasts, LEDs use drivers. Even though the function of ballasts and drivers are quite similar, most documentation prefers ‘drivers’ to be associated with LED lamps and ‘ballasts’ to other traditional light sources. Ballasts and drivers are essential components to trigger and control the light fixtures.

Source: LED Drivers vs. Light Ballasts | IKIO

Source: custom rom with dex | XDA Forums

Source: [ROM][10] hadesRom Q v3.0 for Exynos S8 / S8+ / Note8 [04.02.2022] | XDA Forums