: I need to develop a software that takes mp3 mono files and converts them into stereo mp3 files where one channel (left or right) carries the mono file, and the other one is silenced.
: I will be using it to mix different files so that different messages are played on right and left speakers.
I suppose that could be done, but consider this first. MP3 is a lossy format and already suffers sound degredation, even at 256k. Now, if you were to play the audio and re-encode it, you'd lose more sound quality from an already lossy format. It would be best to either go frmo MP3 to a stereo wave, or re-rip the MP3 the way you want it.