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Converting AMR to MP3 29 October 2009

Posted by Oliver Mason in misc.

For a teaching project, students were required to audio record a group discussion meeting. For this they could either use a digital recorder, or any other recording equipment they had available. One group used a mobile phone, and we managed to transfer the audio file from the phone to my MacBook using Bluetooth.

Initially I was surprised at the small size of the file: 4.5 MB for a recording of about 50 mins. The quality is of course poor, but AMR does a pretty good job of keeping it small. The equivalent MP3 file comes in at 22.5 MB.

But there was a problem: dealing with AMR files. I cannot load it into my version of Audacity to convert it to MP3, but perhaps there’s a plug-in somewhere. I was not able to immediately find one. Then I found that Quicktime can play back AMR files, and save them in other formats, but for that you need to fork out money to get the Pro version. I then tried out iMovie, and managed to import the file as the sound track of a yet to complete movie. Attempts to extract the audio were fruitless; but then I accidentally noticed that the sound track was referred to as ‘aiff’ file. I opened the movie project package, and, hey presto, there was an aiff file. iMovie had converted it during the import.

So now I could import that into Audacity, and export from there to MP3.



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