iPhone - AVAudioRecorder - how can I record to an mp3?

Question

I am using the AVAudioRecorder class available with the 3.0 SDK to record audio in my app. I am successfully able to record to a caf/aiff file. But I would like to record to an mp3.

I tried changing some values in the settings dictionary but all I get is a blank file.

1. Is it possible to record to an mp3 using AVAudioRecorder

2. If not, how can I transfer the caf files from my app to a computer?

Thanks.

Solution 1

From all I can find on the API documentation, you can't change the encoder. The only encoder settings I could find that you can change are:

AVEncoderAudioQualityKey;
AVEncoderBitRateKey;
AVEncoderBitDepthHintKey;

As for transferring the file, a typical approach would be to email the file.

Solution 2

See:

http://developer.apple.com/iphone/library/qa/qa2008/qa1615.html

IMA is a 4:1 format, which means it will compress to 25% of the original size. It's good enough for voice, but not ideal for music.

Lossless is great for music, but usually only gets 50%.

µLaw and aLaw are older formats that compress to 50%, but are much worse than Lossless.

I haven't used iLBC.

I'd bet you'll never see an MP3 encoder made available to third-party apps due to licensing issues.

Comments

[Vaerenberg]

A 3-4 minute caf file would be about 30-40 MB! How can we email such a big file? How does the FourTrack app let user access the wav files using IP address? Thanks for the answer!

[Vaerenberg]

what about m4a? The new voice memo app included with the 3.0 saves the memos in m4a format. So will the AVAudioRecorder also allow saving .m4a files? Thanks

[Erich Mirabal]

typically yes, but not just mp3, or even audio. en.wikipedia.org/wiki/Bit_rate#Bitrates_in_multimedia

[csakii]

developer.apple.com/iphone/library/qa/qa2008/qa1615.html This Q&A talks about recording a compressed CAF file, but doesn't mention m4a as a possibility. If you're recording voice data, one of the listed voice-quality encoders will save a lot of space over uncompressed audio. For high-quality recordings, Apple Lossless will be roughly 50% of the size of uncompressed data.

[memmons]

iLBC is good for voice recording. It runs about 7MB for an hour of recording.