Record audio on iPhone with smallest file size

Question

I want to record audio with iPhone and then upload it to server.

I could record the audio, but my question is about which format should I use to record audio, so that the Recorder will result a file with smallest file size.

Answer 1

Here are the results for few encoding supported by iPhone. Size of audio file in KB of duration 10 sec.

kAudioFormatMPEG4AAC : 164,

kAudioFormatAppleLossless : 430,

kAudioFormatAppleIMA4 : 475,

kAudioFormatULaw : 889,

kAudioFormatALaw : 889,

Among these kAudioFormatMPEG4AAC is having smallest size.

Answer 2

Apple iOS supports playback audio in these formats:

1. AAC (MPEG-4 Advanced Audio Coding)
2. ALAC (Apple Lossless)
3. HE-AAC (MPEG-4 High Efficiency AAC)
4. iLBC (internet Low Bitrate Codec, another format for speech)
5. IMA4 (IMA/ADPCM)
6. Linear PCM (uncompressed, linear pulse code modulation)
7. MP3 (MPEG-1 audio layer 3)
8. µ-law and a-law

For recording following formats are possible:

1. AAC (MPEG-4 Advanced Audio Coding)
2. ALAC (Apple Lossless)
3. iLBC (internet Low Bitrate Codec, for speech)
4. IMA4 (IMA/ADPCM)
5. Linear PCM (uncompressed, linear pulse-code modulation)
6. µ-law and a-law

while only AAC supports hardware-assisted encoding (see Apple iOS SDK documentation)

For the universality in availability I prefer MP3.

Check these links to find exact code to record audio - Recording Audio on an iPad with AVAudioRecorder