How do I force single (only) channel audio in youtube/flash videos to play in both (left/right) channels?

Occasionally, I find Youtube videos that have only one audio channel (only left or only right); example video (left channel only).

This is quite annoying, especially with headphones on, as I hear sound in one ear, and no sound in the other.

So, I want to be able to easily force dual mono (Left+Left or Right+Right) when I find that kind of video, and switch to normal stereo after I finish watching it.

• I have my headphones plugged well / I don't create audio/video - I want it for real-time playback only,
• In Windows audio config, setting balance 100% to Left / Right doesn't help (I have either still only left when moved to left, and no sound at all when moved to right), I've checked all the configurations in Control Panel > Sounds and Audio Devices > Audio > Sound Playback > Advanced like suggested in this post, in conjunction with moving balance left/right, and it doesn't seem to have any impact on actual sound I hear in headphones,
• No need to mix L with R, I just want L+L or R+R,
• I prefer software solutions to buying a stereo-to-mono adapter,
• Free solutions please, no $$$ ones, neither trials etc.,

• In Control Panel > Realtek HD Sound Effect Manager I can turn on various mumbo-jumbo effects like: Concert Hall / Hangar / Bathroom / whatever environment (and in fact it makes the sound appear in two ears, but well, it's ridiculous to do this;), but there is no Dual Mono option.

• Finally, I know I can force L+L or R+R in VLC Player which supports Youtube (well, a little hack is needed, because Youtube internals change from time to time) but it is not very convenient to launch VLC just to play Youtube video - I want to keep it in the browser, I use Firefox generally (but well, if I don't find easier way, I will launch it in VLC).

Solution 1:

I just accidentally found a lame and hacky but working way to solve the issue - plug the headphones halfway, instead of fully, to the port :)

Solution 2:

Windows 10:

Windows Settings > Ease of access > Audio, and on the right panel just toggle "Turn mono audio" to "ON".

Original answer now obsolete in updated Windows 10: Windows Settings>Ease of access> Other options> Audio options: Turn mono audio "ON".

Solution 3:

Free, no additional software required for most: Use any basic "vocal cancellation" or "Headphone Virtualization" feature. It is offered by many audio drivers, e.g. with the standard Realtek driver, presents in most Windows systems:

Right click on the loadspeaker symbol in taskbar, click "Playback devices". Right click on the active audio device, go to the tab "Enhancements". Check "Immediate Mode", uncheck "Disable all sound effects" (Already default). Check "Vocal cancellation" or "Headphone Virtualization".

(Works for all audio with sound only on the right or left channel. Reason: Simple voice cancellation works by duplicating and inverting the audio of one channel and adding it to the other channel, resulting in a cancellation of the central audio. If only one channel has sound, we just get the desired duplication.)

Solution 4:

Right click on sound volume in taskbar, playback devices.

Right click on active audio device.

Properties -> Levels

Balance, set left / right till it sounds ok.

Remember to reset after the one video, or you'll then be deaf in that ear.