Question

我正在从iphone音频输入中读取缓冲区数据。我有一个延迟，我不能在50ms的变化分辨率。

这是我的类，我打电话来获取缓冲区音频数据 - 我需要知道如何设置延迟更低，是否可以通过某种方式更改缓冲区大小，或我需要remoteIO
要做到这一点。非常感谢：

#import "SoundSensor.h"

@interface SoundSensor (Private)

- (void)updateLevels;
- (void)setupQueue;
- (void)setupFormat;
- (void)setupBuffers;
- (void)setupMetering;

@end


static SoundSensor *sharedListener = nil;

static void listeningCallback(void *inUserData, AudioQueueRef inAQ, AudioQueueBufferRef inBuffer, const AudioTimeStamp *inStartTime, UInt32 inNumberPacketsDescriptions, const AudioStreamPacketDescription *inPacketDescs)
{
    NSLog(@"listeningCallback "); 
    SoundSensor *listener = (SoundSensor *)inUserData;
    if ([listener isListening])
        AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL);

}

@implementation SoundSensor





+ (SoundSensor *)sharedListener {
    @synchronized(self) {
        if (sharedListener == nil)
            [[self alloc] init];
    }
    NSLog(@"sharedListener ");
    return sharedListener;
}

- (void)dealloc {
    [sharedListener stop];
    [super dealloc];
}

#pragma mark -
#pragma mark Listening






- (void)listen {
    NSLog(@"listen");
    if (queue == nil)
        [self setupQueue];
    AudioQueueStart(queue, NULL);
}

- (void)pause {
    NSLog(@"pause  ");
    if (![self isListening])

        return;

    AudioQueueStop(queue, true);
}

- (void)stop {
    NSLog(@"stop  ");
    if (queue == nil)
        return;

    AudioQueueDispose(queue, true);
    queue = nil;
}

- (BOOL)isListening {
    if (queue == nil)
        return NO;

    UInt32 isListening, ioDataSize = sizeof(UInt32);
    OSStatus result = AudioQueueGetProperty(queue, kAudioQueueProperty_IsRunning, &isListening, &ioDataSize);
    return (result != noErr) ? NO : isListening;
}

#pragma mark -
#pragma mark Levels getters

- (Float32)averagePower {   
    if (![self isListening])
        return 0.0;
    float tmp = [self levels][0].mAveragePower;
    tmp = tmp * 100;    
    return tmp;
}

- (Float32)peakPower {
    if (![self isListening])
        return 0.0;

    return [self levels][0].mPeakPower;
}

- (AudioQueueLevelMeterState *)levels {
    if (![self isListening])
        return nil;

    [self updateLevels];
    return levels;
}

- (void)updateLevels {
    UInt32 ioDataSize = format.mChannelsPerFrame * sizeof(AudioQueueLevelMeterState);
    AudioQueueGetProperty(queue, (AudioQueuePropertyID)kAudioQueueProperty_CurrentLevelMeter, levels, &ioDataSize);
}

#pragma mark -
#pragma mark Setup

- (void)setupQueue {
    NSLog(@"setupQueue");
    if (queue)
        return;

    [self setupFormat];
    [self setupBuffers];
    AudioQueueNewInput(&format, listeningCallback, self, NULL, NULL, 0, &queue);
    [self setupMetering];   
}

- (void)setupFormat {
    NSLog(@"setupFormat ");
#if TARGET_IPHONE_SIMULATOR
    format.mSampleRate = 44100.0;
#else
    UInt32 ioDataSize = sizeof(sampleRate);
    AudioSessionGetProperty(kAudioSessionProperty_CurrentHardwareSampleRate, &ioDataSize, &sampleRate);
    format.mSampleRate = sampleRate;
#endif
    format.mFormatID = kAudioFormatLinearPCM;
    format.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    format.mFramesPerPacket = format.mChannelsPerFrame = 1;
    format.mBitsPerChannel = 16;
    format.mBytesPerPacket = format.mBytesPerFrame = 2;
}

- (void)setupBuffers {
    NSLog(@"setupBuffers ");
    AudioQueueBufferRef buffers[3];
    for (NSInteger i = 0; i < 3; ++i) { 
        AudioQueueAllocateBuffer(queue, 735, &buffers[i]); 
        AudioQueueEnqueueBuffer(queue, buffers[i], 0, NULL); 
    }
}

- (void)setupMetering {
    NSLog(@"setupMetering");
    levels = (AudioQueueLevelMeterState *)calloc(sizeof(AudioQueueLevelMeterState), format.mChannelsPerFrame);
    UInt32 trueValue = true;
    AudioQueueSetProperty(queue, kAudioQueueProperty_EnableLevelMetering, &trueValue, sizeof(UInt32));
}

#pragma mark -
#pragma mark Singleton Pattern

+ (id)allocWithZone:(NSZone *)zone {
    NSLog(@"allocWithZone");
    @synchronized(self) {
        if (sharedListener == nil) {
            sharedListener = [super allocWithZone:zone];
            return sharedListener;
        }
    }

    return nil;
}

- (id)copyWithZone:(NSZone *)zone {
    NSLog(@"copyWithZone");
    return self;
}

- (id)init {
    if ([super init] == nil)
        return nil;

    return self;
}

- (id)retain {
    return self;
}

- (unsigned)retainCount {
    return UINT_MAX;
}

- (void)release {
    // Do nothing.
}

- (id)autorelease {
    return self;
}

@end

Answer 1

使用RemoteIO Audio Unit进行录制，并结合为kAudioSessionProperty_PreferredHardwareIOBufferDuration音频会话属性设置适当的小值（尝试5.8毫秒），似乎提供比使用Audio Queue API进行录制要低得多的延迟。使用RemoteIO音频单元进行输入时，您必须使用某种形式的DSP包络跟踪代码（甚至可能是频谱加权）从原始PCM样本计算您自己的电平计量值。没有内置的API直接为RemoteIO提供。

使用kAudioQueueProperty_CurrentLevelMeter似乎不是为低延迟而设计或配置的。

音频输入延迟

1 个答案: