Merging/Combining 2 audio files? mplayer?mendoer?ffmpeg?flvtool2?

Hi i have a quick question since i cannot find a answer on google. I have a site where users can upload music. They can trim the music to whatever they want using mplayer. Users can only listen to the trimmed duration they set until they purchase the song then it unlocks and plays the full file. What i want to do is this, instead of trimming the music, i want to add a voice tag and let the audio play full with a vocal tag on top of it as one so it cannot be downloaded. I'm not sure what is the right word combine? merge? but i want to take lets say a instrumental, and a voice tag that says something both mp3s. I want to put them into one file. here is the code im using now. $CFG['admin']['musics']['mplayer_convert_command'] = '{mplayer_path} {source_file} -ao pcm:file={output_file}'; $CFG['admin']['musics']['mplayer_trim_command'] = '{mplayer_path} -ss {start_pos} -endpos {end_pos} {source_file} -ao pcm:file={output_file}'; $CFG['admin']['musics']['mplayer_dumpaudio_command'] = '{mplayer_path} -dumpaudio {source_file} -dumpfile {output_file}'; $CFG['admin']['musics']['lame_command'] = '{lame_path} {source_file} -o {output_file}'; $CFG['admin']['musics']['flvtool2_command'] = '{flvtool2_path} -UP {source_file}'; $CFG['admin']['musics']['yamdi_command'] = '{yamdi_path} -i {source_file} -o {output_file}'; if it is possible i would like to do it after this line $CFG['admin']['musics']['mplayer_convert_command'] = '{mplayer_path} {source_file} -ao pcm:file={output_file}'; before its trimmed. and then let it go from there.