4Videosoft All Music Converter for Mac is a conversion tool. You can use this application to convert your audio files into different formats. Some of the supported formats are AAC, AC3, AIFF, AMR, AU, FLAC, MP3, M4A, MP2, OGG, WAV, and WMA.
Although this is an audio converter, you can also load video files. You can extract the audio track of these files and save it into one of the supported audio formats. When you do this, you discard the video track and only keep the audio track. There is also a video editor, which you can use to trim your video files before extracting their audio track. It is very useful if you want to create an audio file from a long video clip and only want a part of it. I know some people use apps like this one to convert music videos into MP3 files, for example.
In my testing, I was able to open an MKV file and trim it and then save it into an MP3 file. The resulting file sounds very nice on iTunes. I also tried converting MP3 files to AAC and M4A, and I didn't face any problems.