aubio | a library for audio and music analysis | Audio Utils library

MP3 is an interesting format. The underlying data is stored in 'Frames', each 0.026 seconds long. Each frame is a Fast Fourier transform of the sound wave, encoded with varying degrees of quality depending on the size and bitrate, etc.. In your case, are you certain that the mp3s have matching bitrates? If they do, a relatively straightforward grep-style approach should be possible, given that you select on Frame boundaries. However, it is entirely likely and possible that this is not the case.

For a true solution, you need to process the mp3 file to some degree, to abstract away the encoding. However, there is no guarantee that the resulting wave match even for matching sounds, as bitrates and possibly frame alignment may differ. This small degree of chance makes it much harder.

I will give you my approach to this problem, but it is worth noting that this is not the perfect way to do things, just my best swing. Even though its the same file, there's no guarantee that frame boundaries are aligned, so I think you need to take a very wave-oriented approach, rather than a data-oriented one.

First, convert the mp3s to waves. I know that it'd be great to leave it compressed, but again I think wave-oriented is our only hope. Then, use a high-pass filter to try to remove any artifacts of audio compression that would differ between samples. Once you have two waveforms, it should be relatively straight forward to find the wavelet in the wave. You can iterate through possible starting positions and subtract the waves. When you get close to zero, you know you're close.