Как я могу записать разговор / телефонный звонок на iOS?

вы идете. Полный рабочий пример. Твик должен быть загружен в mediaserverd демон. Он будет записывать каждый телефонный звонок в /var/mobile/Media/DCIM/result.m4a. Аудиофайл имеет два канала. Слева-микрофон, справа-динамик. На iPhone 4S вызов записывается только при включенном динамике. На iPhone 5, 5C и 5S вызов записывается в любом случае. Там могут быть небольшие икоты при переключении на / из динамика, но запись будет продолжаться.

#import <AudioToolbox/AudioToolbox.h>
#import <libkern/OSAtomic.h>

//CoreTelephony.framework
extern "C" CFStringRef const kCTCallStatusChangeNotification;
extern "C" CFStringRef const kCTCallStatus;
extern "C" id CTTelephonyCenterGetDefault();
extern "C" void CTTelephonyCenterAddObserver(id ct, void* observer, CFNotificationCallback callBack, CFStringRef name, void *object, CFNotificationSuspensionBehavior sb);
extern "C" int CTGetCurrentCallCount();
enum
{
    kCTCallStatusActive = 1,
    kCTCallStatusHeld = 2,
    kCTCallStatusOutgoing = 3,
    kCTCallStatusIncoming = 4,
    kCTCallStatusHanged = 5
};

NSString* kMicFilePath = @"/var/mobile/Media/DCIM/mic.caf";
NSString* kSpeakerFilePath = @"/var/mobile/Media/DCIM/speaker.caf";
NSString* kResultFilePath = @"/var/mobile/Media/DCIM/result.m4a";

OSSpinLock phoneCallIsActiveLock = 0;
OSSpinLock speakerLock = 0;
OSSpinLock micLock = 0;

ExtAudioFileRef micFile = NULL;
ExtAudioFileRef speakerFile = NULL;

BOOL phoneCallIsActive = NO;

void Convert()
{
    //File URLs
    CFURLRef micUrl = CFURLCreateWithFileSystemPath(NULL, (CFStringRef)kMicFilePath, kCFURLPOSIXPathStyle, false);
    CFURLRef speakerUrl = CFURLCreateWithFileSystemPath(NULL, (CFStringRef)kSpeakerFilePath, kCFURLPOSIXPathStyle, false);
    CFURLRef mixUrl = CFURLCreateWithFileSystemPath(NULL, (CFStringRef)kResultFilePath, kCFURLPOSIXPathStyle, false);

    ExtAudioFileRef micFile = NULL;
    ExtAudioFileRef speakerFile = NULL;
    ExtAudioFileRef mixFile = NULL;

    //Opening input files (speaker and mic)
    ExtAudioFileOpenURL(micUrl, &micFile);
    ExtAudioFileOpenURL(speakerUrl, &speakerFile);

    //Reading input file audio format (mono LPCM)
    AudioStreamBasicDescription inputFormat, outputFormat;
    UInt32 descSize = sizeof(inputFormat);
    ExtAudioFileGetProperty(micFile, kExtAudioFileProperty_FileDataFormat, &descSize, &inputFormat);
    int sampleSize = inputFormat.mBytesPerFrame;

    //Filling input stream format for output file (stereo LPCM)
    FillOutASBDForLPCM(inputFormat, inputFormat.mSampleRate, 2, inputFormat.mBitsPerChannel, inputFormat.mBitsPerChannel, true, false, false);

    //Filling output file audio format (AAC)
    memset(&outputFormat, 0, sizeof(outputFormat));
    outputFormat.mFormatID = kAudioFormatMPEG4AAC;
    outputFormat.mSampleRate = 8000;
    outputFormat.mFormatFlags = kMPEG4Object_AAC_Main;
    outputFormat.mChannelsPerFrame = 2;

    //Opening output file
    ExtAudioFileCreateWithURL(mixUrl, kAudioFileM4AType, &outputFormat, NULL, kAudioFileFlags_EraseFile, &mixFile);
    ExtAudioFileSetProperty(mixFile, kExtAudioFileProperty_ClientDataFormat, sizeof(inputFormat), &inputFormat);

    //Freeing URLs
    CFRelease(micUrl);
    CFRelease(speakerUrl);
    CFRelease(mixUrl);

    //Setting up audio buffers
    int bufferSizeInSamples = 64 * 1024;

    AudioBufferList micBuffer;
    micBuffer.mNumberBuffers = 1;
    micBuffer.mBuffers[0].mNumberChannels = 1;
    micBuffer.mBuffers[0].mDataByteSize = sampleSize * bufferSizeInSamples;
    micBuffer.mBuffers[0].mData = malloc(micBuffer.mBuffers[0].mDataByteSize);

    AudioBufferList speakerBuffer;
    speakerBuffer.mNumberBuffers = 1;
    speakerBuffer.mBuffers[0].mNumberChannels = 1;
    speakerBuffer.mBuffers[0].mDataByteSize = sampleSize * bufferSizeInSamples;
    speakerBuffer.mBuffers[0].mData = malloc(speakerBuffer.mBuffers[0].mDataByteSize);

    AudioBufferList mixBuffer;
    mixBuffer.mNumberBuffers = 1;
    mixBuffer.mBuffers[0].mNumberChannels = 2;
    mixBuffer.mBuffers[0].mDataByteSize = sampleSize * bufferSizeInSamples * 2;
    mixBuffer.mBuffers[0].mData = malloc(mixBuffer.mBuffers[0].mDataByteSize);

    //Converting
    while (true)
    {
        //Reading data from input files
        UInt32 framesToRead = bufferSizeInSamples;
        ExtAudioFileRead(micFile, &framesToRead, &micBuffer);
        ExtAudioFileRead(speakerFile, &framesToRead, &speakerBuffer);
        if (framesToRead == 0)
        {
            break;
        }

        //Building interleaved stereo buffer - left channel is mic, right - speaker
        for (int i = 0; i < framesToRead; i++)
        {
            memcpy((char*)mixBuffer.mBuffers[0].mData + i * sampleSize * 2, (char*)micBuffer.mBuffers[0].mData + i * sampleSize, sampleSize);
            memcpy((char*)mixBuffer.mBuffers[0].mData + i * sampleSize * 2 + sampleSize, (char*)speakerBuffer.mBuffers[0].mData + i * sampleSize, sampleSize);
        }

        //Writing to output file - LPCM will be converted to AAC
        ExtAudioFileWrite(mixFile, framesToRead, &mixBuffer);
    }

    //Closing files
    ExtAudioFileDispose(micFile);
    ExtAudioFileDispose(speakerFile);
    ExtAudioFileDispose(mixFile);

    //Freeing audio buffers
    free(micBuffer.mBuffers[0].mData);
    free(speakerBuffer.mBuffers[0].mData);
    free(mixBuffer.mBuffers[0].mData);
}

void Cleanup()
{
    [[NSFileManager defaultManager] removeItemAtPath:kMicFilePath error:NULL];
    [[NSFileManager defaultManager] removeItemAtPath:kSpeakerFilePath error:NULL];
}

void CoreTelephonyNotificationCallback(CFNotificationCenterRef center, void *observer, CFStringRef name, const void *object, CFDictionaryRef userInfo)
{
    NSDictionary* data = (NSDictionary*)userInfo;

    if ([(NSString*)name isEqualToString:(NSString*)kCTCallStatusChangeNotification])
    {
        int currentCallStatus = [data[(NSString*)kCTCallStatus] integerValue];

        if (currentCallStatus == kCTCallStatusActive)
        {
            OSSpinLockLock(&phoneCallIsActiveLock);
            phoneCallIsActive = YES;
            OSSpinLockUnlock(&phoneCallIsActiveLock);
        }
        else if (currentCallStatus == kCTCallStatusHanged)
        {
            if (CTGetCurrentCallCount() > 0)
            {
                return;
            }

            OSSpinLockLock(&phoneCallIsActiveLock);
            phoneCallIsActive = NO;
            OSSpinLockUnlock(&phoneCallIsActiveLock);

            //Closing mic file
            OSSpinLockLock(&micLock);
            if (micFile != NULL)
            {
                ExtAudioFileDispose(micFile);
            }
            micFile = NULL;
            OSSpinLockUnlock(&micLock);

            //Closing speaker file
            OSSpinLockLock(&speakerLock);
            if (speakerFile != NULL)
            {
                ExtAudioFileDispose(speakerFile);
            }
            speakerFile = NULL;
            OSSpinLockUnlock(&speakerLock);

            Convert();
            Cleanup();
        }
    }
}

OSStatus(*AudioUnitProcess_orig)(AudioUnit unit, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inNumberFrames, AudioBufferList *ioData);
OSStatus AudioUnitProcess_hook(AudioUnit unit, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inNumberFrames, AudioBufferList *ioData)
{
    OSSpinLockLock(&phoneCallIsActiveLock);
    if (phoneCallIsActive == NO)
    {
        OSSpinLockUnlock(&phoneCallIsActiveLock);
        return AudioUnitProcess_orig(unit, ioActionFlags, inTimeStamp, inNumberFrames, ioData);
    }
    OSSpinLockUnlock(&phoneCallIsActiveLock);

    ExtAudioFileRef* currentFile = NULL;
    OSSpinLock* currentLock = NULL;

    AudioComponentDescription unitDescription = {0};
    AudioComponentGetDescription(AudioComponentInstanceGetComponent(unit), &unitDescription);
    //'agcc', 'mbdp' - iPhone 4S, iPhone 5
    //'agc2', 'vrq2' - iPhone 5C, iPhone 5S
    if (unitDescription.componentSubType == 'agcc' || unitDescription.componentSubType == 'agc2')
    {
        currentFile = &micFile;
        currentLock = &micLock;
    }
    else if (unitDescription.componentSubType == 'mbdp' || unitDescription.componentSubType == 'vrq2')
    {
        currentFile = &speakerFile;
        currentLock = &speakerLock;
    }

    if (currentFile != NULL)
    {
        OSSpinLockLock(currentLock);

        //Opening file
        if (*currentFile == NULL)
        {
            //Obtaining input audio format
            AudioStreamBasicDescription desc;
            UInt32 descSize = sizeof(desc);
            AudioUnitGetProperty(unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &desc, &descSize);

            //Opening audio file
            CFURLRef url = CFURLCreateWithFileSystemPath(NULL, (CFStringRef)((currentFile == &micFile) ? kMicFilePath : kSpeakerFilePath), kCFURLPOSIXPathStyle, false);
            ExtAudioFileRef audioFile = NULL;
            OSStatus result = ExtAudioFileCreateWithURL(url, kAudioFileCAFType, &desc, NULL, kAudioFileFlags_EraseFile, &audioFile);
            if (result != 0)
            {
                *currentFile = NULL;
            }
            else
            {
                *currentFile = audioFile;

                //Writing audio format
                ExtAudioFileSetProperty(*currentFile, kExtAudioFileProperty_ClientDataFormat, sizeof(desc), &desc);
            }
            CFRelease(url);
        }
        else
        {
            //Writing audio buffer
            ExtAudioFileWrite(*currentFile, inNumberFrames, ioData);
        }

        OSSpinLockUnlock(currentLock);
    }

    return AudioUnitProcess_orig(unit, ioActionFlags, inTimeStamp, inNumberFrames, ioData);
}

__attribute__((constructor))
static void initialize()
{
    CTTelephonyCenterAddObserver(CTTelephonyCenterGetDefault(), NULL, CoreTelephonyNotificationCallback, NULL, NULL, CFNotificationSuspensionBehaviorHold);

    MSHookFunction(AudioUnitProcess, AudioUnitProcess_hook, &AudioUnitProcess_orig);
}

несколько слов о том, что происходит. - это используется для обработки аудио потоков для того, чтобы применить некоторые эффекты, смешивать, конвертировать и т. д. Мы зацепили AudioUnitProcess для доступа к звуковым потокам телефонного звонка. В то время как телефонный звонок активен, эти потоки обрабатываются различными способами.

мы слушаем уведомления CoreTelephony, чтобы получить изменения статуса телефонного звонка. Когда мы получаем образцы звука, нам нужно определить, откуда они берутся - микрофон или динамик. Это делается с помощью