I've been trying to prepend an audio mp3 file to a recorded mp3. The recorded mp3 is mono channel (having 1 channel as I made it record). I want the user of my app to select any audio file say mp3 and prepend that to my recorded file. The selected file can be multichannel but the recorded file is 1 channel. Is this possible using any tool. I tried using sox with the following command
sox input1.mp3 input2.mp3 output.mp3
but this gives error that the input files must have same number of channels. Thanks for the help.