How can I append to a recorded MPEG4 AAC file?

Question

I\'m recording audio on an iPhone, using an AVAudioRecorder with the following settings:

NSMutableDictionary *recordSettings = [[NSDictionary alloc]         


        

Answer 1

I found a way that was much faster to implement:

1. Use AVAudioRecorder and use the extension "m4a" for a temporary file, you can however also use "caf" if you want but it's unnecessary.

2. Modify the code here to use AVAssetExportPresetPassthrough and exportSession.outputFileType = AVFileTypeQuickTimeMovie and a filename "audioJoined.mov". Use your newly recorded temporary m4a and an existing m4a file. This gives you an instant join (no recompression) and produces a "mov".

Note. Unfortunately the AVAudioPlayer cannot play a "mov" so the next step is to convert it to something playable. However, if you are just going to share the file somewhere you could potentially skip the next step since the mov is perfectly playable on a Mac in Quicktime. It also can be played in iTunes and synced back to an iPhone and plays in the iPod app.

3. Convert the mov back to a m4a using [[AVAssetExportSession alloc] initWithAsset:movFileAsset presetName:AVAssetExportPresetAppleM4A], @"audioJoined.m4a" for the filename and exportSession.outputFileType = AVFileTypeAppleM4A. Again, this is instant. I'm guessing that the exporter is smarter in this situation when it starts with a mov asset rather than a AVMutableComposition asset.

I'm using this technique in an app that is able to resume recording after recording has been stopped and the file has been played, or even if the app is restarted, pretty cool.