iOS Code to Convert m4a to WAV

Question

Does anyone have any code snippets that show how to convert an M4a file to WAV? I know there are libraries that convert the other way around.

Thanks.

see this once may be it helps you http://stackoverflow.com/questions/31452202/ios-swift-merge-and-convert-wav-files-to-mp3 — Anbu.Karthik, Mar 02 '16 at 03:49

score 12 · Answer 1 · answered Jun 03 '17 at 01:48

Just to update for Swift 3:

func convertAudio(_ url: URL, outputURL: URL) {
    var error : OSStatus = noErr
    var destinationFile: ExtAudioFileRef? = nil
    var sourceFile : ExtAudioFileRef? = nil

    var srcFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()
    var dstFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()

    ExtAudioFileOpenURL(url as CFURL, &sourceFile)

    var thePropertySize: UInt32 = UInt32(MemoryLayout.stride(ofValue: srcFormat))

    ExtAudioFileGetProperty(sourceFile!,
                            kExtAudioFileProperty_FileDataFormat,
                            &thePropertySize, &srcFormat)

    dstFormat.mSampleRate = 44100  //Set sample rate
    dstFormat.mFormatID = kAudioFormatLinearPCM
    dstFormat.mChannelsPerFrame = 1
    dstFormat.mBitsPerChannel = 16
    dstFormat.mBytesPerPacket = 2 * dstFormat.mChannelsPerFrame
    dstFormat.mBytesPerFrame = 2 * dstFormat.mChannelsPerFrame
    dstFormat.mFramesPerPacket = 1
    dstFormat.mFormatFlags = kLinearPCMFormatFlagIsPacked |
    kAudioFormatFlagIsSignedInteger

    // Create destination file
    error = ExtAudioFileCreateWithURL(
        outputURL as CFURL,
        kAudioFileWAVEType,
        &dstFormat,
        nil,
        AudioFileFlags.eraseFile.rawValue,
        &destinationFile)
    print("Error 1 in convertAudio: \(error.description)")

    error = ExtAudioFileSetProperty(sourceFile!,
                                    kExtAudioFileProperty_ClientDataFormat,
                                    thePropertySize,
                                    &dstFormat)
    print("Error 2 in convertAudio: \(error.description)")

    error = ExtAudioFileSetProperty(destinationFile!,
                                    kExtAudioFileProperty_ClientDataFormat,
                                    thePropertySize,
                                    &dstFormat)
    print("Error 3 in convertAudio: \(error.description)")

    let bufferByteSize : UInt32 = 32768
    var srcBuffer = [UInt8](repeating: 0, count: 32768)
    var sourceFrameOffset : ULONG = 0

    while(true){
        var fillBufList = AudioBufferList(
            mNumberBuffers: 1,
            mBuffers: AudioBuffer(
                mNumberChannels: 2,
                mDataByteSize: UInt32(srcBuffer.count),
                mData: &srcBuffer
            )
        )
        var numFrames : UInt32 = 0

        if(dstFormat.mBytesPerFrame > 0){
            numFrames = bufferByteSize / dstFormat.mBytesPerFrame
        }

        error = ExtAudioFileRead(sourceFile!, &numFrames, &fillBufList)
        print("Error 4 in convertAudio: \(error.description)")

        if(numFrames == 0){
            error = noErr;
            break;
        }

        sourceFrameOffset += numFrames
        error = ExtAudioFileWrite(destinationFile!, numFrames, &fillBufList)
        print("Error 5 in convertAudio: \(error.description)")
    }

    error = ExtAudioFileDispose(destinationFile!)
    print("Error 6 in convertAudio: \(error.description)")
    error = ExtAudioFileDispose(sourceFile!)
    print("Error 7 in convertAudio: \(error.description)")
}

Is there any other changes to export to MP3 other than using kAudioFileMP3Type? I'm getting a a nil crash on error = ExtAudioFileSetProperty(destinationFile!, when using MP3 type — miOS, Aug 21 '17 at 10:00
You may need to try a different mFormatFlags. You'll noticed that that was a difference between this one and the accepted answer other than kAudioFileMP3Type. — MScottWaller, Aug 21 '17 at 22:53

score 4 · Answer 2 · answered Mar 28 '18 at 20:31

Here is an Objective-C version of MScottWaller's Swift 3 answer. You need to @import AudioToolbox.

-(void) convertAudio:(NSURL*)url outputURL:(NSURL*)outputURL
{
    OSStatus error = noErr;
    ExtAudioFileRef destinationFile = nil;
    ExtAudioFileRef sourceFile = nil;

    AudioStreamBasicDescription srcFormat;
    AudioStreamBasicDescription dstFormat;

    ExtAudioFileOpenURL((__bridge CFURLRef)url, &sourceFile);


    UInt32 thePropertySize = sizeof(srcFormat); //UInt32(MemoryLayout.stride(ofValue: srcFormat));;
    ExtAudioFileGetProperty(sourceFile, kExtAudioFileProperty_FileDataFormat, &thePropertySize, &srcFormat);

    dstFormat.mSampleRate = 44100;  //Set sample rate
    dstFormat.mFormatID = kAudioFormatLinearPCM;
    dstFormat.mChannelsPerFrame = 1;
    dstFormat.mBitsPerChannel = 16;
    dstFormat.mBytesPerPacket = 2 * dstFormat.mChannelsPerFrame;
    dstFormat.mBytesPerFrame = 2 * dstFormat.mChannelsPerFrame;
    dstFormat.mFramesPerPacket = 1;
    dstFormat.mFormatFlags = kLinearPCMFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger;

    // Create destination file
    error = ExtAudioFileCreateWithURL(
                                      (__bridge CFURLRef)outputURL,
                                      kAudioFileWAVEType,
                                      &dstFormat,
                                      nil,
                                      kAudioFileFlags_EraseFile,
                                      &destinationFile);
    NSLog(@"Error 1 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);

    error = ExtAudioFileSetProperty(sourceFile,
                                    kExtAudioFileProperty_ClientDataFormat,
                                    thePropertySize,
                                    &dstFormat);
    NSLog(@"Error 2 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);

    error = ExtAudioFileSetProperty(destinationFile,
                                    kExtAudioFileProperty_ClientDataFormat,
                                    thePropertySize,
                                    &dstFormat);
    NSLog(@"Error 3 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);

    const UInt32 bufferByteSize = 32768;
    UInt8 srcBuffer[bufferByteSize];// = [UInt8](repeating: 0, count: 32768)
    memset(srcBuffer, 0, bufferByteSize);
    unsigned long sourceFrameOffset = 0;

    while(true)
    {
        AudioBufferList fillBufList;
        fillBufList.mNumberBuffers = 1;
        fillBufList.mBuffers[0].mNumberChannels = 2;
        fillBufList.mBuffers[0].mDataByteSize = bufferByteSize;
        fillBufList.mBuffers[0].mData = &srcBuffer;

        UInt32 numFrames = 0;

        if(dstFormat.mBytesPerFrame > 0){
            numFrames = bufferByteSize / dstFormat.mBytesPerFrame;
        }

        error = ExtAudioFileRead(sourceFile, &numFrames, &fillBufList);
        NSLog(@"Error 4 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);

        if(numFrames == 0)
        {
            error = noErr;
            break;
        }

        sourceFrameOffset += numFrames;
        error = ExtAudioFileWrite(destinationFile, numFrames, &fillBufList);
        NSLog(@"Error 5 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);
    }

    error = ExtAudioFileDispose(destinationFile);
    NSLog(@"Error 6 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);
    error = ExtAudioFileDispose(sourceFile);
    NSLog(@"Error 7 in convertAudio: %d - %@", error, [NSError errorWithDomain:NSOSStatusErrorDomain code:error userInfo:nil].description);
}

score 3 · Accepted Answer · answered Mar 15 '16 at 01:45

If anyone else needs some code to do this here it is in Swift

func convertAudioFile(sourceURL: CFURLRef, destinationURL: 
CFURLRef, outputFormat: OSType , 
outputSampleRate: Float64) ->  OSStatus
{
var error : OSStatus = noErr
var destinationFile : ExtAudioFileRef = nil
var sourceFile : ExtAudioFileRef = nil

var srcFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()
var dstFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()

var audioConverter : AudioConverterRef = nil

audioConverter = AudioConverterRef.init()

ExtAudioFileOpenURL(sourceURL, &sourceFile)

var thePropertySize: UInt32 = UInt32(strideofValue(srcFormat))

ExtAudioFileGetProperty(sourceFile, kExtAudioFileProperty_FileDataFormat, &thePropertySize, &srcFormat)

dstFormat.mSampleRate = (outputSampleRate == 0 ? srcFormat.mSampleRate : outputSampleRate)  //Set sample rate

dstFormat.mFormatID = outputFormat
dstFormat.mChannelsPerFrame = 1
dstFormat.mBitsPerChannel = 16
dstFormat.mBytesPerPacket = 2 * dstFormat.mChannelsPerFrame
dstFormat.mBytesPerFrame = 2 * dstFormat.mChannelsPerFrame
dstFormat.mFramesPerPacket = 1
dstFormat.mFormatFlags = kLinearPCMFormatFlagIsPacked | kLinearPCMFormatFlagIsSignedInteger // little-endian

//Create destination file
ExtAudioFileCreateWithURL(destinationURL, kAudioFileCAFType, &dstFormat, nil,
    AudioFileFlags.EraseFile.rawValue, &destinationFile)

ExtAudioFileSetProperty(sourceFile, kExtAudioFileProperty_ClientDataFormat, thePropertySize, &dstFormat)
ExtAudioFileSetProperty(destinationFile, kExtAudioFileProperty_ClientDataFormat, thePropertySize, &dstFormat)

var size : UInt32 = UInt32(strideofValue(audioConverter))

ExtAudioFileGetProperty(destinationFile, kExtAudioFileProperty_AudioConverter, &size, &audioConverter)

var canResume : UInt32 = 0

size = UInt32(strideofValue(canResume))

error = AudioConverterGetProperty(audioConverter, kAudioConverterPropertyCanResumeFromInterruption, &size, &canResume)

let bufferByteSize : UInt32 = 32768
var srcBuffer = [UInt8](count: 32768, repeatedValue: 0)

var sourceFrameOffset : ULONG = 0

print("Converting audio file")

while(true){

    var fillBufList = AudioBufferList(
        mNumberBuffers: 1,
        mBuffers: AudioBuffer(
            mNumberChannels: 2,
            mDataByteSize: UInt32(srcBuffer.count),
            mData: &srcBuffer
        )  
    )

    var numFrames : UInt32 = 0

    if(dstFormat.mBytesPerFrame > 0){
        numFrames = bufferByteSize / dstFormat.mBytesPerFrame
    }

    ExtAudioFileRead(sourceFile, &numFrames, &fillBufList)

    if(numFrames == 0){
        error = noErr;
        break;
    }

    sourceFrameOffset += numFrames

    error = ExtAudioFileWrite(destinationFile, numFrames, &fillBufList)
}

ExtAudioFileDispose(destinationFile)
ExtAudioFileDispose(sourceFile)

let audioAsset = AVURLAsset.init(URL: destinationURL, options: nil)
if(audioAsset.duration.seconds < 5.0){
    error = -2500
}

return error;

Which `OSType` and `outputSampleRate` should I pass if I want to convert a m4a file to a wav one? — Cesare, Jun 26 '16 at 21:40
Yes. you want to use OSType of kAudioFormatLinearPCM and the outputSampleRate of 16000 — O2U, Jun 28 '16 at 01:35
**Swift 3** for `AIFF` format at http://stackoverflow.com/a/41437453/218152 — SwiftArchitect, Jan 03 '17 at 06:23
Old code.. This one Got working without AudioConverterRef in swift 5 check this https://stackoverflow.com/a/65522764/4524195 — Nihas Nizar, Dec 31 '20 at 15:34

score 1 · Answer 4 · answered Dec 31 '20 at 15:30

I was trying to convert m4a to Wav format in Swift 5.

All the above codes are outdated and was not working. After few tweaks done and here is the working example

func convertAudio(_ url: URL, outputURL: URL) {
    var error : OSStatus = noErr
    var destinationFile : ExtAudioFileRef? = nil
    var sourceFile : ExtAudioFileRef? = nil

    var srcFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()
    var dstFormat : AudioStreamBasicDescription = AudioStreamBasicDescription()

    ExtAudioFileOpenURL(url as CFURL, &sourceFile)

    var thePropertySize: UInt32 = UInt32(MemoryLayout.stride(ofValue: srcFormat))

    ExtAudioFileGetProperty(sourceFile!,
        kExtAudioFileProperty_FileDataFormat,
        &thePropertySize, &srcFormat)
    
    dstFormat.mSampleRate = 44100  //Set sample rate
    dstFormat.mFormatID = kAudioFormatLinearPCM
    dstFormat.mChannelsPerFrame = 1
    dstFormat.mBitsPerChannel = 16
    dstFormat.mBytesPerPacket = 2 * dstFormat.mChannelsPerFrame
    dstFormat.mBytesPerFrame = 2 * dstFormat.mChannelsPerFrame
    dstFormat.mFramesPerPacket = 1
    dstFormat.mFormatFlags = kLinearPCMFormatFlagIsPacked |
    kAudioFormatFlagIsSignedInteger


    // Create destination file
    error = ExtAudioFileCreateWithURL(
        outputURL as CFURL,
        kAudioFileWAVEType,
        &dstFormat,
        nil,
        AudioFileFlags.eraseFile.rawValue,
        &destinationFile)
    reportError(error: error)

    error = ExtAudioFileSetProperty(sourceFile!,
            kExtAudioFileProperty_ClientDataFormat,
            thePropertySize,
            &dstFormat)
    reportError(error: error)

    error = ExtAudioFileSetProperty(destinationFile!,
                                     kExtAudioFileProperty_ClientDataFormat,
                                    thePropertySize,
                                    &dstFormat)
    reportError(error: error)

    let bufferByteSize : UInt32 = 32768
    var srcBuffer = [UInt8](repeating: 0, count: 32768)
    var sourceFrameOffset : ULONG = 0

    while(true){
        var fillBufList = AudioBufferList(
            mNumberBuffers: 1,
            mBuffers: AudioBuffer(
                mNumberChannels: 2,
                mDataByteSize: UInt32(srcBuffer.count),
                mData: &srcBuffer
            )
        )
        var numFrames : UInt32 = 0

        if(dstFormat.mBytesPerFrame > 0){
            numFrames = bufferByteSize / dstFormat.mBytesPerFrame
        }

        error = ExtAudioFileRead(sourceFile!, &numFrames, &fillBufList)
        reportError(error: error)

        if(numFrames == 0){
            error = noErr;
            break;
        }
        
        sourceFrameOffset += numFrames
        error = ExtAudioFileWrite(destinationFile!, numFrames, &fillBufList)
        reportError(error: error)
    }
    
    error = ExtAudioFileDispose(destinationFile!)
    reportError(error: error)
    error = ExtAudioFileDispose(sourceFile!)
    reportError(error: error)
}

func reportError(error: OSStatus) {
    // Handle error
    print(error)
}

score 0 · Answer 5 · answered Mar 02 '16 at 05:56

0

AVAssetReader and AVAssetWriter in the AVFoundation framework can be used read AAC files and write that data as WAV/RIFF files on iOS devices. There's sample code on the Apple developer site. It's a bit more than a short snippet.

answered Mar 02 '16 at 05:56

hotpaw2

70,107
14
90
153

Thanks use that's what I'm working through right now. I'm converting the code to Swift since that sample code is using C++. – O2U Mar 03 '16 at 07:28

score 0 · Answer 6 · answered Dec 21 '16 at 10:32

0

Here is an edit to @O2U answere. As above code does not actually convert it to wave file. Please use "kAudioFileWAVEType" instead of "kAudioFileCAFType" in above code at line //Create destination file ExtAudioFileCreateWithURL(destinationURL, kAudioFileCAFType, &dstFormat, nil, AudioFileFlags.EraseFile.rawValue, &destinationFile)

answered Dec 21 '16 at 10:32

Harsh Thakur

293
2
11

Did you change anything else? Is not setting the destinationFile when I use `kAudioFileWAVEType` – Marcos Griselli Mar 20 '17 at 22:45
No , haven't change anything else than this. Please check your destination url is correct or not, that may be the issue in case destination file is not set. – Harsh Thakur Mar 23 '17 at 07:21
@MarcosGriselli Got it working. while changing to **kAudioFileWAVEType** you have to add respective flags also **kLinearPCMFormatFlagIsPacked**. Check This https://stackoverflow.com/a/65522764/4524195 – Nihas Nizar Dec 31 '20 at 15:38

Anirudha Mahale · Answer 7 · 2019-02-16T05:45:12.653

-3

I simply changed the extension of the file to .wav and removed the .m4a file and it worked.

func getDirectory() -> URL {
    let path = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    let documentDirectory = path[0]
    return documentDirectory
}

let date = Date().timeIntervalSince1970

fileName = getDirectory().appendingPathComponent("\(date).m4a")
wavFileName = getDirectory().appendingPathComponent("\(date).wav")

try! FileManager.default.copyItem(at: fileName, to: wavFileName)
try! FileManager.default.removeItem(at: fileName)

I even played .wav file and it's working fine.

audioPlayer = try! AVAudioPlayer(contentsOf: wavFileName)
audioPlayer.play()

Are there any drawbacks for converting the file extension from .m4a to .wav like this?

edited Feb 16 '19 at 05:45

answered Feb 16 '19 at 05:17

Anirudha Mahale

2,526
3
37
57

I am actually interested in knowing about the drawbacks too. I always change file extensions and don't see any consequences. Maybe the one who downvoted your answer would care to explain? – Celeste Apr 24 '20 at 09:33
Yeah I also don't see any drawbacks, can you upvote it? – Anirudha Mahale Apr 24 '20 at 11:45

iOS Code to Convert m4a to WAV

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