How to get audio data from a MP3?

Question

I'm working on an application that has to process audio files. When using mp3 files I'm not sure how to handle data (the data I'm interested in are the the audio bytes, the ones that represent what we hear).

If I'm using a wav file I know I have a 44 bytes header and then the data. When it comes to an mp3, I've read that they are composed by frames, each frame containing a header and audio data. Is it possible to get all the audio data from a mp3 file?

I'm using java (I've added MP3SPI, Jlayer, and Tritonus) and I'm able to get the bytes from the file, but I'm not sure about what these bytes represent or how to handle then.

Answer 1

From the documentation for MP3SPI:

File file = new File(filename);
AudioInputStream in= AudioSystem.getAudioInputStream(file);
AudioInputStream din = null;
AudioFormat baseFormat = in.getFormat();
AudioFormat decodedFormat = new AudioFormat(AudioFormat.Encoding.PCM_SIGNED, 
                                            baseFormat.getSampleRate(),
                                            16,
                                            baseFormat.getChannels(),
                                            baseFormat.getChannels() * 2,
                                            baseFormat.getSampleRate(),
                                            false);
din = AudioSystem.getAudioInputStream(decodedFormat, in);

You then just read data from din - it will be the "raw" data as per decodedFormat. (See the docs for AudioFormat for more information.)

(Note that this sample code doesn't close the stream or anything like that - use appropriate try/finally blocks as normal.)

Answer 2

The data that you want are the actual samples, while MP3 represents the data differently. So, like what everyone else has said - you need a library to decode the MP3 data into actual samples for your purpose.