How can I control media volume from a 3-button in-line remote? I have the standard HTC RC-E160 headset with 3 buttons and a mic. I can use the button in the middle to pause and play music tracks, and I can use the buttons on each side to jump to next or previous track. Is there a way I can use these buttons to increase or decrease the volume? I am thinking maybe something like quickly pressing one of the buttons two times to increase the volume by one increment? Is something like this possible?

Maybe I need a Bluetooth headset? Or a wired headset with a 5 button remote control?

I am using MortPlayer Music as my primary music player and it has some options to set the button action for the headset but I see no options for volume control.
You can use a headset controller app from the playstore (e.g. Jays or Philips Headset or HeadsetButton Controller) to use the "middle button" for that. Might take a few tries to find the correct app (if one doesn't work fine, try another -- I did the same and finally found one working perfectly, see my answer here). I'm not sure if they affect the other two buttons at all, or if you even could configure them -- but they allow me (having a headset with a single button) to perfom all the most necessary functions like play/pause, skip, vol+ and vol- with a single button.