I learned here that the documentation says that there are supposedly tools to make MP3s seamlessly loop. What are they (on OS X)? I've never heard about this sort of thing before and Googling hasn't found me anything.
Not sure of specific tools as such, but I believe the issue with seamless looping of MP3 is mainly due to padding silence to frames, where a frame is a fixed number of samples (1152 acording to the page below ) and a few other idiosyncrasies.
This Make Gapless MP3 page should help. The important information is at the bottom of the page (Theory of operation), though I noticed some programs are mentioned at the start.
The sad answer seems to be that none of these tools create seamless mp3 loops, nor is there any information on the web about any such tools. SoundForge will pad with both encoder delay and 1152 samples at beginning and end. Audacity adds 1152 samples to the beginning, Logic to the end. I even tried the solution suggested through CompuPhase using their MP3Loop utility and that pads the beginning with 1152 samples of silence. It seems the only non-hack solution would be for Unity to handle the resampling of the audio files when compressing them, or to start compressed sound playback at 1153 samples into the audio file (which definitely qualifies as a horrible hack). If anyone hears of a viable working solution, please let us know!
It's worth mentioning that FMOD Soundbank Generator (FSBank) makes seamless looping MP3s for use in FMOD (Unity's sound engine). I'm not sure if Unity supports the FSB format, but if it doesn't it probably should since it offers better performance than loose files.
Yes it’s possible, here’s how to do it under windows:
http://www.compuphase.com/mp3/mp3loops.htm
I’m not aware of a mac alternative…
This does it under windows:
http://www.compuphase.com/mp3/mp3loops.htm
I’m not sure if there’s an alternative for mac though…
from what im guessing you want to make a loop that doesnt click or pause during the end and restart. in order to do this you will need audio editing software to get a good end result. the best tool for the job is a program called cool edit later taken over by adobe and now called adobe audition.
logic or most music creation software will leave a small gap, but this wont. the idea is to cut the wave at exactly 0 making a smooth sine wae. this will remove popping and clicking, however that being said you still need to find a point to cut it at where the sound should loop, i can post a video tutorial if needed
I wrote up a post that explains how to create seamless looping files and convert them for in game use! It should answer any questions you have 
If anyone is still interested in this, there is a totally automatic gapless MP3 looping player developed by Music Library company Lemoncake. Its not commercially available yet, but contact me if you would like to know more.
I maid an Asset play mp3 files, it works on Win, Max, Linux, iOS, android…
It works for local files and web streams.
This will play your songs and decode them into a unity audiosource.
Asset - uAudio: Mp3 Player/Streamer
Free Audacity I use Sony Soundforge which I got included in the Sony Video Vegas Platinum Pro Pack for about $100. It includes a video editor, Audio Editor, DVD Architect and Cinescore. Cinescore is no longer sold by Sony, not as a stand alone or included in any of their packages. (Except any lingering 9.0 versions of the Platinum Pro Pack.
Now those software can be used to create seamless loop sound tracks, but you have to create it using the software. I am not aware of anything you can click and choose nighttime, crickets, running creek water, light breeze, 30 seconds and select Endless Loop and then render.
It might exists or may be in the making somewhere on the web. Try Googling Endless Loop generator.