iOS and decoding MP3/AAC data from memory buffer

Question

Forgive me, I very new at iOS - and programming at this scale in general.

I have been digging through iOS documentation, I know there are some functions like ExtAudiofile... for decoding MP3/AAC files, but are there any that will operate on Mp3/aac data that's already in memory?

I will probably have to extract the media data (byte by byte; iOS does allow that right?) from inside another file, so I can't just give it the URL.

Edit: the mp3 data will be in a non-standard file format, Apple provided function should not be able to read them. I heard iOS has a hardware decoder that works on one audio stream and the OS will fallback to software decoding if there are multiple streams.

I would rather use what Apple provides then integrate a MP3 decoder into the app.

Answer 1

You can use ExtAudioFileRead to read a file that is in memory, but you have to use AudioFileOpenWithCallbacks. I'm not by my work computer so I can't give you exact code, but here's the general process:

• Use fopen/fread to read the given file into a memory buffer array. Use a simple C array and not an NSArray or NSData - you need speed and you need for it to be compatible with the next step.
• Create some basic C function callbacks for read / get size.
• Use AudioFileOpenWithCallbacks with the callbacks you wrote to open the audio file in memory.
• Use ExtAudioFileWrapAudioFileID to start decoding the file in memory. This is in replacement of ExtAudioFileOpenURL.

If you Google +AudioFileOpenWithCallbacks +ExtAudioFileWrapAudioFileID, you'll find that some folks have already done this and published their code.

I'm not sure what you mean by non-standard mp3 data, so you should try to play the file using another app to see if it will be compatible.