如何在iOS和Xcode中记录完美的循环

Question

我已经为此挣扎了大约一年了，现在我试图确定我的问题并将其呈现给其他人。

我一直在写一个应用程序，依赖于'GarageBand'像录音。也就是说，我想记录用户正好8拍，然后我想让他们能够循环这个。我同时为用户播放节拍器(用户将戴着耳机听到节拍器，记录到他们设备上的麦克风)

我可以设法打开录音大约4.8秒。6*8节拍)，计时器显示它运行了4.8秒，但我的音频记录总是比4.8秒短一点。就像4.78或4.71，会导致循环不正常。

我尝试了AVAudioRecorder,AudioQueue和AudioUnits，认为后一种方法可能会解决我的问题。

我使用ntimer每0.6秒发射一次，为节拍器播放短暂的信号。4拍后，节拍器定时器的功能，打开记录器节拍器，等待4.6秒停止记录。

我使用时间间隔来计算地铁运行的时间(在4.800xxx时看起来很紧)，并将其与音频文件的持续时间进行比较，音频文件总是不同的。

我希望我可以附加我的项目，但我想我只能解决附加我的头和实现。要进行测试，您必须创建一个具有以下IB特征的项目:

录制，播放，停止按钮歌曲/曲目持续时间标签定时器持续时间标签调试标签

如果你启动应用程序，然后点击记录，你被"计数"与4拍，然后录音机开始。用手指轻敲桌子，直到录音机停止。再拍8下(共12下)，录音机停止。

你可以在显示中看到录制的音轨比4.8秒短一点，在某些情况下，短得多，导致音频不能正常循环。

有谁知道我能做些什么来收紧这个吗?谢谢你的阅读。

下面是我的代码:

//
//  ViewController.h
//  speakagain
//
//  Created by NOTHING on 2014-03-18.
//
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import "CoreAudio/CoreAudioTypes.h"
#import <AudioToolbox/AudioQueue.h>
#import <AudioToolbox/AudioFile.h>
#import <AVFoundation/AVFoundation.h>
@interface ViewController : UIViewController
{
    IBOutlet UIButton *btnRecord;
    IBOutlet UIButton *btnPlay;
    IBOutlet UIButton *btnStop;
    IBOutlet UILabel *debugLabel;
    IBOutlet UILabel *timerDuration;
    IBOutlet UILabel *songDuration;
    //UILabel *labelDebug;
    struct AQRecorderState {
        AudioStreamBasicDescription  mDataFormat;
        AudioQueueRef                mQueue;
        AudioQueueBufferRef          mBuffers[kNumberBuffers];
        AudioFileID                  mAudioFile;
        UInt32                       bufferByteSize;
        SInt64                       mCurrentPacket;
        bool                         mIsRunning;                    // 8
    };
    struct AQRecorderState aqData;
    AVAudioPlayer *audioPlayer;
    NSString *songName;
    NSTimer *recordTimer;
    NSTimer *metroTimer;
    NSTimeInterval startTime, endTime, elapsedTime;
    int inputBuffer;
    int beatNumber;
}
@property (nonatomic, retain)   IBOutlet UIButton *btnRecord;
@property (nonatomic, retain)   IBOutlet UIButton *btnPlay;
@property (nonatomic, retain)   IBOutlet UIButton *btnStop;
@property (nonatomic, retain)   IBOutlet UILabel *debugLabel;
@property (nonatomic, retain) IBOutlet UILabel *timerDuration;
@property (nonatomic, retain) IBOutlet UILabel *songDuration;

- (IBAction) record;
- (IBAction) stop;
- (IBAction) play;
static void HandleInputBuffer (void *aqData,AudioQueueRef inAQ,AudioQueueBufferRef inBuffer,const AudioTimeStamp *inStartTime, UInt32 inNumPackets,const AudioStreamPacketDescription  *inPacketDesc);
@end

实现:

//
    //  ViewController.m
    //  speakagain
    //
    //  Created by NOTHING on 2014-03-18.
    //
    #import "ViewController.h"

    @interface ViewController ()
    @end
    @implementation ViewController
    @synthesize btnPlay, btnRecord,btnStop,songDuration, timerDuration, debugLabel;

    - (void)viewDidLoad
    {
        debugLabel.text = @"";
        songName =[[NSString alloc ]init];
        //NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        //NSString *documentsDirectory = [paths objectAtIndex:0];
        songName = @"TestingQueue.caf";

        [super viewDidLoad];
        // Do any additional setup after loading the view, typically from a nib.
    }
    - (void)prepareAudioQueue
    {
        //struct AQRecorderState *pAqData;
        inputBuffer=0;
        aqData.mDataFormat.mFormatID         = kAudioFormatLinearPCM;
        aqData.mDataFormat.mSampleRate       = 44100.0;
        aqData.mDataFormat.mChannelsPerFrame = 1;
        aqData.mDataFormat.mBitsPerChannel   = 16;
        aqData.mDataFormat.mBytesPerPacket   =
        aqData.mDataFormat.mBytesPerFrame = aqData.mDataFormat.mChannelsPerFrame * sizeof (SInt16);
        aqData.mDataFormat.mFramesPerPacket  = 1;
        //    AudioFileTypeID fileType             = kAudioFileAIFFType;
        AudioFileTypeID fileType             = kAudioFileCAFType;
        aqData.mDataFormat.mFormatFlags = kLinearPCMFormatFlagIsBigEndian| kLinearPCMFormatFlagIsSignedInteger| kLinearPCMFormatFlagIsPacked;
        AudioQueueNewInput (&aqData.mDataFormat,HandleInputBuffer, &aqData,NULL, kCFRunLoopCommonModes, 0,&aqData.mQueue);
        UInt32 dataFormatSize = sizeof (aqData.mDataFormat);
        // in Mac OS X, instead use
        //    kAudioConverterCurrentInputStreamDescription
        AudioQueueGetProperty (aqData.mQueue,kAudioQueueProperty_StreamDescription,&aqData.mDataFormat,&dataFormatSize);
        //Verify
        NSFileManager *fileManager = [NSFileManager defaultManager];
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *txtPath = [documentsDirectory stringByAppendingPathComponent:songName];
        NSLog(@"INITIALIZING FILE");
        if ([fileManager fileExistsAtPath:txtPath] == YES) {
            NSLog(@"PREVIOUS FILE REMOVED");
            [fileManager removeItemAtPath:txtPath error:nil];
        }

        const char *filePath = [txtPath UTF8String];
        CFURLRef audioFileURL = CFURLCreateFromFileSystemRepresentation ( NULL,(const UInt8 *) filePath,strlen (filePath),false );
        AudioFileCreateWithURL (audioFileURL,fileType,&aqData.mDataFormat, kAudioFileFlags_EraseFile,&aqData.mAudioFile );
        DeriveBufferSize (aqData.mQueue,aqData.mDataFormat,0.5,&aqData.bufferByteSize);
        for (int i = 0; i < kNumberBuffers; ++i)
        {
            AudioQueueAllocateBuffer (aqData.mQueue,aqData.bufferByteSize,&aqData.mBuffers[i]);
            AudioQueueEnqueueBuffer (aqData.mQueue,aqData.mBuffers[i], 0,NULL );
        }
    }
    - (void) metronomeFire
    {
        if(beatNumber < 5)
        {
            //count in time.
            // just play the metro beep but don't start recording
            debugLabel.text = @"count in (1,2,3,4)";
            [self playSound];
        }
        if(beatNumber == 5)
        {
            //start recording
            aqData.mCurrentPacket = 0;
            aqData.mIsRunning = true;
            startTime = [NSDate timeIntervalSinceReferenceDate];
            recordTimer = [NSTimer scheduledTimerWithTimeInterval:4.8 target:self selector:@selector(killTimer) userInfo:nil repeats:NO];
            AudioQueueStart (aqData.mQueue,NULL);
            debugLabel.text = @"Recording for 8 beats (1,2,3,4 1,2,3,4)";
            [self playSound];
        }
        else if (beatNumber < 12)
        {   //play metronome from beats 6-16
            [self playSound];
        }
        if(beatNumber == 12)
        {
            [metroTimer invalidate]; metroTimer = nil;
            [self playSound];
        }
        beatNumber++;
    }
    - (IBAction) play
    {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *txtPath = [documentsDirectory stringByAppendingPathComponent:songName];
        NSURL *url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@",txtPath]];
        if (audioPlayer)
        {
            [audioPlayer stop];
            audioPlayer = nil;
        }
        NSError *error;
        audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:&error];
        if (audioPlayer == nil)
        {
            NSLog(@"%@",[error description]);
        }
        else
        {
            [audioPlayer play];
            [audioPlayer setNumberOfLoops:-1];
        }
    }
    - (void) killTimer
    {
        //this is the timer function.  Runs once after 4.8 seconds.
       [self stop];
    }
    - (IBAction) stop
    {
        if (audioPlayer)
        {
            [audioPlayer stop];
            audioPlayer = nil;

        }
        else
        {
            if(metroTimer)
            {
                [metroTimer invalidate];metroTimer = nil;
            }
            //Stop the audio queue
            AudioQueueStop (aqData.mQueue,true);
            aqData.mIsRunning = false;
            AudioQueueDispose (aqData.mQueue,true);
            AudioFileClose (aqData.mAudioFile);
            //Get elapsed time of timer
            endTime = [NSDate timeIntervalSinceReferenceDate];
            elapsedTime = endTime - startTime;
            //Get elapsed time of audio file
            NSArray *pathComponents = [NSArray arrayWithObjects:
                                       [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject],
                                       songName,
                                       nil];
            NSURL *audioFileURL = [NSURL fileURLWithPathComponents:pathComponents];
            AVURLAsset* audioAsset = [AVURLAsset URLAssetWithURL:audioFileURL options:nil];
            CMTime audioDuration = audioAsset.duration;
            float audioDurationSeconds = CMTimeGetSeconds(audioDuration);
            //Log values
            NSLog(@"Track Duration: %f",audioDurationSeconds);
            NSLog(@"Timer Duration: %.6f", elapsedTime);
            //Show values on GUI too
            songDuration.text = [NSString stringWithFormat: @"Track Duration: %f",audioDurationSeconds];
            timerDuration.text = [NSString stringWithFormat:@"Timer Duration: %@",[NSString stringWithFormat: @"%.6f", elapsedTime]];
            debugLabel.text = @"Why is the duration of the track less than the duration the timer ran?";
        }

    }
    -(void) playSound
    {
        NSString *path = [[NSBundle mainBundle] pathForResource:@"blip2" ofType:@"aif"];
        SystemSoundID soundID;
        AudioServicesCreateSystemSoundID((__bridge CFURLRef)[NSURL fileURLWithPath:path],  &soundID);
        AudioServicesPlaySystemSound (soundID);
    }
    - (IBAction) record
    {
        [self prepareAudioQueue];
        songDuration.text = @"";
        timerDuration.text = @"";
        //debugLabel.text = @"Please wait 12 beats (The first four are count in)";
        //init beat number
        beatNumber = 1;
        //safe guard
        if(aqData.mIsRunning)
        {
            AudioQueueStop (aqData.mQueue,true);
            aqData.mIsRunning = false;
            AudioQueueDispose (aqData.mQueue,true);
            AudioFileClose (aqData.mAudioFile);
        }
        //start count in (metro will start recording)
        //aqData.mCurrentPacket = 0;
        //aqData.mIsRunning = true;
        startTime = [NSDate timeIntervalSinceReferenceDate];
        metroTimer = [NSTimer scheduledTimerWithTimeInterval:.6 target:self selector:@selector(metronomeFire) userInfo:nil repeats:YES];
        //recordTimer = [NSTimer scheduledTimerWithTimeInterval:4.8 target:self selector:@selector(killTimer) userInfo:nil repeats:NO];
        //AudioQueueStart (aqData.mQueue,NULL);
    }
    static void HandleInputBuffer (void *aqData,AudioQueueRef inAQ,AudioQueueBufferRef inBuffer,const AudioTimeStamp *inStartTime,UInt32 inNumPackets,const AudioStreamPacketDescription *inPacketDesc)
    {
        //boiler plate
        NSLog(@"HandleInputBuffer");
        struct AQRecorderState *pAqData = (struct AQRecorderState *) aqData;
        if (inNumPackets == 0 && pAqData->mDataFormat.mBytesPerPacket != 0)
            inNumPackets = inBuffer->mAudioDataByteSize / pAqData->mDataFormat.mBytesPerPacket;
        if (AudioFileWritePackets (pAqData->mAudioFile,false,inBuffer->mAudioDataByteSize,inPacketDesc,pAqData->mCurrentPacket,&inNumPackets,inBuffer->mAudioData) == noErr)
        {
            pAqData->mCurrentPacket += inNumPackets;
        }
        if (pAqData->mIsRunning == 0)
            return;
        AudioQueueEnqueueBuffer (pAqData->mQueue,inBuffer,0,NULL);
    }
    void DeriveBufferSize(AudioQueueRef audioQueue,AudioStreamBasicDescription ASBDescription,Float64 seconds,UInt32 *outBufferSize)
    {
        //boiler plate
        static const int maxBufferSize = 0x50000;
        int maxPacketSize = ASBDescription.mBytesPerPacket;
        if(maxPacketSize == 0)
        {
            UInt32 maxVBRPacketSize = sizeof(maxPacketSize);
            AudioQueueGetProperty(audioQueue, kAudioQueueProperty_MaximumOutputPacketSize, &maxPacketSize, &maxVBRPacketSize);
            NSLog(@"max buffer = %d",maxPacketSize);
        }
        Float64 numBytesForTime = ASBDescription.mSampleRate * maxPacketSize * seconds;
        *outBufferSize = (UInt32)(numBytesForTime < maxBufferSize ? numBytesForTime : maxBufferSize);
    }
    OSStatus SetMagicCookieForFile (AudioQueueRef inQueue, AudioFileID inFile)
    {
        //boiler plate
        OSStatus result = noErr;
        UInt32 cookieSize;
        if (AudioQueueGetPropertySize (inQueue,kAudioQueueProperty_MagicCookie,&cookieSize) == noErr)
        {
            char* magicCookie =(char *) malloc (cookieSize);
            if (AudioQueueGetProperty (inQueue,kAudioQueueProperty_MagicCookie,magicCookie,&cookieSize) == noErr)
            {
                result =    AudioFileSetProperty (inFile,kAudioFilePropertyMagicCookieData,cookieSize,magicCookie);
            }
            free (magicCookie);
        }
        return result;
    }






    - (void)didReceiveMemoryWarning
    {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    @end

Answer 1

这是一个很大的主题，所以我怀疑你会得到一个足够大的答案来重新构建你所提供的代码。但是，我可以给你链接，将提供绝大多数你需要的。

第一件事是NSTimer永远不会工作，由于同步问题。同样，忽略AudioQueue和AVAudioRecorder。只有AudioUnit是低水平的，足以满足您的需要。

看看我的答案:

iOS流音频从一个iOS设备到另一个

但是真正的金矿——以及你需要非常熟悉的知识——是Tasty Pixel的博客。Tasty Pixel是Loopy HD的供应商，但也有人很好地分享了一些非常深入的知识。

:

用于音频处理的简单、快速的循环缓冲区实现

开发loop，第2部分:实现

和

使用RemoteIO音频单元

最后，确保你熟悉数据包、帧、样本等。