Sound Equalizer for PC Videos and maybe Android?

For Windows:

sourceforge.net/projects/equalizerapo/

Very easy to set up, works as a system wide equalizer. Very low latency and low cpu load. It's the best windows EQ, if you're asking me and it's released under the GNU General Public License.

For Android:

That's a hard one. Really hard. Some Android ROMs have their build-in EQ. I'm using LineageOS(a fork of Android) and it comes with "AudioFX" which sometimes works or sometimes, it doesn't. A lot of people have huge issues running EQs on Android, as there seems to be a problem with lost audio focus/application focus which is needed, in order to modify sound.

There's only one good solution for Android and that's to install a driver based EQ, which doesn't cause problems with audio focus and works as a system wide EQ. Viper is excellent, but the installation is quite complicated and I'd not recommend using Viper, unless you have a deep understanding how Android and Android devices work. First release of Viper was back in 2013 and with each iteration it got better and better.

forum.xda-developers.com/showthread.php?t=2191223

Forget about Android equalizer apps: They don't work well. I tried a lot of them, even bought one, but they all got their issues.

Hope I could shed some light on this topic. If you have further questions, just let me know.