How do you make mono audio track playback in stereo in Ubuntu?

Every once in a while I'll come across a video that I want to watch (whether it be youtube or otherwise), and the sound, for whatever reason, will be only coming out one speaker. It's not a problem with my hardware, or any kind of configuration; it's because whoever encoded the video, messed up the audio. If I used speakers this wouldn't be a problem, but 100% of my listening is done with headphones. This makes for a very annoying experience. You'd think something like this hardly ever happens, but it seems I come across this more than most people, and it;s really annoying.

One easy fix is to pull out the earphone plug a little, which causes one channel to be send through both ear speakers. This works, but the slightest tug of the wire sends the plug out completely. Also, sometimes if it's the left channel that's only playing, the "half way out" method will not work because it'll just send the right side (the quiet side) through both speakers.

There has to be some kind of program that sits between the sound system and the output jack that can make all sound mono?

Updated for VLC 2.2.1:

1. Tools > Preferences > Audio > Output. Select ALSA Audio Output.
2. Tools > Preferences. Select the "all" radio button at the bottom.
   • Audio > Output modules > ALSA. Select the mono option from the Audio output channels dropdown menu.
3. Restart VLC

Original answer:

You can use VLC to do this. But I had trouble getting the mono to actually work. Here's what ended up working for me:

1. Tools > Preferences > Audio > Output. Select ALSA Audio Output.
2. Tools > Preferences. Select the "all" radio button at the bottom.
   • Audio > Filters. Select the mono option ("audio filter for stereo to mono")
3. Restart VLC

VLC can do it. When playing the video just go Audio ⇨ Audio Channels ⇨ Right/Left.