Fundamentals of Audio and Video Programming for Games (Pro-Developer)

Input files must be mono or stereo. If stereo, the file is mixed down to mono before it gets written to the output file. Input files can be any format that is supported by DirectShow, including WAV, AVI, MP3, and WMV. You can even use video files, as long as they contain an audio stream. (The video stream will be ignored.)

For the output file, the sampling rate and bits per sample are taken from the format of the first input file. If any of the other input files have a different format, they are resampled to match the first input file. For best results, you should use mono input files that all share the same sampling rate and bit depth.

If the input files are unequal in duration, the application writes silence into the output file to pad out the remaining time.