I have to amend this: I’d assumed that “we don’t support mp3” but it seems that isn’t always true – in some cases, we might be able to load an mp3!
It turns out that libsndfile can be compiled with mp3 support – but it isn’t, on my machine (probably because I get libsndfile from Ubuntu packages, and the package has probably been built without mp3). I’m not sure about our binary releases.
In any case, the original example here looks correct, and the most likely problem is failure to read the files, and mp3 may or may not be the problem.
hjh