The "add music" button seems to randomly appear on the videos I upload to YouTube. For example, I uploaded 2 videos without music track, yet only one has the "add music" button:
Any idea why?
- Video 1 (without "add music"): http://www.youtube.com/watch?v=dWbGbflkwvE
- Video 2 (with "add music"): http://www.youtube.com/watch?v=mbzEtwoBi3Q