ios - 为什么 AudioOutputUnitStart() 失败并返回代码 -500？

Question

我正在尝试使用 SDK 8.1 上的 Core Audio 和 AVAudioSession 开发一个分析来自麦克风的音频流的应用程序。使用苹果文档中的点点滴滴以及有用的博主，我成功地组合了一个程序

• 设置 AVAudioSession 的属性。
• 激活 AVAudioSession。
• 实例化音频组件实例。
• 设置音频单元的属性，例如。一个回调函数和一个 AudioStreamDescription。
• 初始化音频单元。

但程序无法开始录音 - AudioOutputUnitStart 函数失败并返回代码 -500。这是为什么？ [如果将以下代码另存为 ViewController.m 并在单页 xcode 模板中使用，则它会按原样运行。即使它不是最小的，我也试图让它尽可能小]。

#import "ViewController.h"
@import AVFoundation;
@import AudioUnit;
#define kInputBus 1
AudioComponentInstance *audioUnit = NULL;
float *convertedSampleBuffer = NULL;
int status = 0;
static OSStatus recordingCallback(void *inRefCon,
                                  AudioUnitRenderActionFlags *ioActionFlags,
                                  const AudioTimeStamp *inTimeStamp,
                                  UInt32 inBusNumber,
                                  UInt32 inNumberFrames,
                                  AudioBufferList *ioData) {
    AudioBufferList *bufferList;
    OSStatus status;
    status = AudioUnitRender(*audioUnit,
                             ioActionFlags,
                             inTimeStamp,
                             inBusNumber,
                             inNumberFrames,
                             bufferList);
    printf("%d", status); printf("%s", " is the return code of AudioUnitRender from the recordingCallback.\n");
    // DoStuffWithTheRecordedAudio(bufferList);
    return noErr;
}
int myAudio() {
    AVAudioSession *mySession = [AVAudioSession sharedInstance];
    [mySession setCategory: AVAudioSessionCategoryRecord error: nil];
    [mySession setMode: AVAudioSessionModeMeasurement error: nil];
    [mySession setPreferredSampleRate:44100 error:nil];
    [mySession setPreferredIOBufferDuration:0.02 error:nil];
    [mySession setActive: YES error: nil];
    audioUnit = (AudioUnit*)malloc(sizeof(AudioUnit));
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    AudioComponent comp = AudioComponentFindNext(NULL, &desc);
    status = AudioComponentInstanceNew(comp, audioUnit);
    printf("%d", status); printf("%s", " is the return code of Instantiating a new audio component instance.\n");
    UInt32 enable = 1;
    status = AudioUnitSetProperty(*audioUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputBus, &enable, sizeof(enable));
    printf("%d", status); printf("%s", " is the return code of EnablingIO on the audiounit.\n");
    AudioStreamBasicDescription streamDescription = {0};
    streamDescription.mSampleRate       = 44100;
    streamDescription.mFormatID         = kAudioFormatLinearPCM;
    streamDescription.mFormatFlags      = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    streamDescription.mFramesPerPacket  = 1;
    streamDescription.mChannelsPerFrame = 1;
    streamDescription.mBitsPerChannel   = 16;
    streamDescription.mBytesPerPacket   = 2;
    streamDescription.mBytesPerFrame    = 2;
    status = AudioUnitSetProperty(*audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &streamDescription, sizeof(streamDescription));
    printf("%d", status); printf("%s", " is the return code of setting the AudioStreamDescription.\n");
    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = recordingCallback;
    callbackStruct.inputProcRefCon = NULL;
    status = AudioUnitSetProperty(*audioUnit,
                                  kAudioOutputUnitProperty_SetInputCallback,
                                  kAudioUnitScope_Global,
                                  kInputBus,
                                  &callbackStruct,
                                  sizeof(callbackStruct));
    printf("%d", status); printf("%s", " is the return code of setting the recording callback on the audiounit\n");
    status = AudioUnitInitialize(*audioUnit);
    printf("%d", status); printf("%s", " is the return code of initializing the audiounit.\n");
    status = AudioOutputUnitStart(*audioUnit);
    printf("%d", status); printf("%s", " is the return code of Starting the audioUnit\n");
    return noErr;
}

@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    myAudio();
    [NSThread sleepForTimeInterval:1];
    exit(0);
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
@end

所有 printf 语句都返回 0，除了最后一个返回 -500。

Answer 1

题中提供的代码有两个错误:

1. 应在音频单元启动后创建 Audio Session 。
2. @jn_pdx 指出必须分配 bufferList。

这是一个完整的 ViewController.m，它可以录音，如果评论 block 被激活，也可以播放(如果你的目标是播放并激活 Audio Session block ，然后改变类别从 Record 到 PlayAndRecord。感谢 Michael Tyson 发布我构建的基础。

#import "ViewController.h"

@interface ViewController ()
@end
@implementation ViewController


@import AVFoundation;
@import AudioUnit;


#define kOutputBus 0
#define kInputBus 1

static OSStatus recordingCallback(void *inRefCon,
                                  AudioUnitRenderActionFlags *ioActionFlags,
                                  const AudioTimeStamp *inTimeStamp,
                                  UInt32 inBusNumber,
                                  UInt32 inNumberFrames,
                                  AudioBufferList *ioData) {

// This works, but can be optimised by moving this code out of the Callback function.

    AudioBufferList *bufferList;
    bufferList = (AudioBufferList *)malloc(sizeof(AudioBufferList) + sizeof(AudioBuffer));
    bufferList->mNumberBuffers = 1;
    bufferList->mBuffers[0].mNumberChannels = 1;
    bufferList->mBuffers[0].mDataByteSize = 1024 * 2;
    bufferList->mBuffers[0].mData = calloc(1024, 2);

    OSStatus status;

    status = AudioUnitRender(inRefCon,
                             ioActionFlags,
                             inTimeStamp,
                             inBusNumber,
                             inNumberFrames,
                             bufferList);
    if (status != noErr) {
        NSLog(@"Error %ld", status);
    } else {
        NSLog(@"No Errors!");
        printf("%d, ",(int)*((SInt16 *)bufferList->mBuffers[0].mData));
    }

    // Now, we have the samples we just read sitting in buffers in bufferList
    // DoStuffWithTheRecordedAudio(bufferList);
    return noErr;
}

//static OSStatus playbackCallback(void *inRefCon,
//                                 AudioUnitRenderActionFlags *ioActionFlags,
//                                 const AudioTimeStamp *inTimeStamp,
//                                 UInt32 inBusNumber,
//                                 UInt32 inNumberFrames,
//                                 AudioBufferList *ioData) {
//    // Notes: ioData contains buffers (may be more than one!)
//    // Fill them up as much as you can. Remember to set the size value in each buffer to match how
//    // much data is in the buffer.
//    return noErr;
//}

- (void)myAudio {



OSStatus status;
AudioComponentInstance audioUnit;

// Describe audio component
AudioComponentDescription desc;
desc.componentType = kAudioUnitType_Output;
desc.componentSubType = kAudioUnitSubType_RemoteIO;
desc.componentFlags = 0;
desc.componentFlagsMask = 0;
desc.componentManufacturer = kAudioUnitManufacturer_Apple;

// Get component
AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);

// Get audio units
status = AudioComponentInstanceNew(inputComponent, &audioUnit);

// Enable IO for recording
UInt32 flag = 1;
status = AudioUnitSetProperty(audioUnit,
                              kAudioOutputUnitProperty_EnableIO,
                              kAudioUnitScope_Input,
                              kInputBus,
                              &flag,
                              sizeof(flag));

//// Enable IO for playback
//status = AudioUnitSetProperty(audioUnit,
//                              kAudioOutputUnitProperty_EnableIO,
//                              kAudioUnitScope_Output,
//                              kOutputBus,
//                              &flag,
//                              sizeof(flag));

// Describe format
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate         = 44100.00;
audioFormat.mFormatID           = kAudioFormatLinearPCM;
audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket    = 1;
audioFormat.mChannelsPerFrame   = 1;
audioFormat.mBitsPerChannel     = 16;
audioFormat.mBytesPerPacket     = 2;
audioFormat.mBytesPerFrame      = 2;

// Apply format
status = AudioUnitSetProperty(audioUnit,
                              kAudioUnitProperty_StreamFormat,
                              kAudioUnitScope_Output,
                              kInputBus,
                              &audioFormat,
                              sizeof(audioFormat));
//status = AudioUnitSetProperty(audioUnit,
//                              kAudioUnitProperty_StreamFormat,
//                              kAudioUnitScope_Input,
//                              kOutputBus,
//                              &audioFormat,
//                              sizeof(audioFormat));
//

// Set input callback
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = audioUnit;
status = AudioUnitSetProperty(audioUnit,
                              kAudioOutputUnitProperty_SetInputCallback,
                              kAudioUnitScope_Global,
                              kInputBus,
                              &callbackStruct,
                              sizeof(callbackStruct));

//// Set output callback
//callbackStruct.inputProc = playbackCallback;
//callbackStruct.inputProcRefCon = audioUnit;
//status = AudioUnitSetProperty(audioUnit,
//                              kAudioUnitProperty_SetRenderCallback,
//                              kAudioUnitScope_Global,
//                              kOutputBus,
//                              &callbackStruct,
//                              sizeof(callbackStruct));

// Initialise
status = AudioUnitInitialize(audioUnit);

// Start
status = AudioOutputUnitStart(audioUnit);
NSLog(@"Starting returned code %ld", status);


//    // It is not necessary to have a session, but if you have one, it must came after the setup of the audiounit.
//    NSError *error = nil;
//    // Configure & activate audio session
//    
//    AVAudioSession *session = [AVAudioSession sharedInstance];
//    
//    if (![session setCategory:AVAudioSessionCategoryRecord error:&error]) NSLog(@"Error configuring session category: %@", error);
//    if (![session setMode:AVAudioSessionModeMeasurement error:&error]) NSLog(@"Error configuring session mode: %@", error);
//    if (![session setActive:YES error:&error]) NSLog(@"Error activating audio session: %@", error);
//    
//    NSLog(@"Session activated. sample rate %f", session.sampleRate);
//    NSLog(@"Number of channels %d", session.inputNumberOfChannels);


}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [self myAudio];
    [NSThread sleepForTimeInterval:1];
    exit(0);
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end