As long as your cords, just under ½ inch thick.
20 yards worsted weight yarn for a short cord (3 1/2-4 feet)
US size 5 double pointed needles
From the Plug Up
Cast on 3 stitches. Pulling yarn behind the cord of the headphones, work the 3 stitches.
Move to end of double pointed needle. Loop yarn behind headphone cord and work the 3 stitches. Repeat, untangling yarn when necessary (which will be often!). Make sure to carefully smooth out the i-cord as you go along so you don't end up with too much or too little and have it bunch up or be too stretched out.
At 1/2 inch before the cord splits in to two, increase 1 st every other row until you have 6 stitches on your needle. Work 1 more row in i-cord. Put 3 stitches on holder (a locking stitch marker works perfectly for this) and put aside.
Work i-cord as before, being careful not to get to many tangles in the yarn or to tangle the yarn with the headphones. Work until flush with cord end (or be daring and increase stitches and work the ears of your headphones if they are ones you can cover and still hear through!).