iphone - 在iPhone上播放第三方库解码的音频

Question

第三方库生成任意所需大小的 16 位带符号立体声样本的顺序缓冲区。我无法弄清楚使用哪些框架/函数来从这些缓冲区中播放。我一直在研究 this answer 中的示例使用 AudioQueue 但它显然在我无法解析的方面不完整(局部变量的使用就好像它们是对象成员、未声明的变量等)。

Apple 的 SpeakHere 示例项目中的代码仅显示如何使用 AudioQueue 播放文件中的音频。有人能指出我正确的方向吗？

Answer 1

想通了。这是一个简单、完整且工作的白噪声生成器，使用从基于Windows的应用程序项目模板创建的AudioQueue。

StaticAppDelegate.h:

//  StaticAppDelegate.h

#import <UIKit/UIKit.h>

// STATIC ADDITIONS
// Add > Existing Frameworks... > AudioToolbox.framework to your Target
#import <AudioToolbox/AudioToolbox.h>
// END STATIC ADDITIONS

@interface StaticAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;

// STATIC ADDITIONS
- (void)startStatic;
- (void)handleBufferCompleteForQueue:(AudioQueueRef)inAQ
                              buffer:(AudioQueueBufferRef)inBuffer;
// END STATIC ADDITIONS

@end

StaticAppDelegate.m:

//  StaticAppDelegate.m

#import "StaticAppDelegate.h"

// STATIC ADDITIONS
#define kNumberBuffers 4
#define kBufferSize 2048

// AudioQueue callback
void AQOutputCallback(
                      void                 *inData,
                      AudioQueueRef        inAQ,
                      AudioQueueBufferRef  inBuffer
                      )
{
    StaticAppDelegate *staticApp = (StaticAppDelegate *)inData;
    [staticApp handleBufferCompleteForQueue:inAQ buffer:inBuffer];
}
// END STATIC ADDITIONS

@implementation StaticAppDelegate

@synthesize window;


- (void)applicationDidFinishLaunching:(UIApplication *)application {    

    // Override point for customization after application launch
    [window makeKeyAndVisible];

    // STATIC ADDITIONS
    [self startStatic];
    // END STATIC ADDITIONS
}

- (void)dealloc {
    [window release];
    [super dealloc];
}

// STATIC ADDITIONS
- (void)startStatic
{
    srandom(time(NULL));

    // initiate audio session
    AudioSessionInitialize(NULL, NULL, NULL, NULL);
    UInt32 category = kAudioSessionCategory_MediaPlayback; // plays through sleep lock and silent switch
    AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, sizeof(category), &category);
    AudioSessionSetActive(true);

    // following is modified from http://stackoverflow.com/questions/1710133/playing-generated-audio-on-an-iphone

    // setup queue
    AudioQueueRef audioQueue;
    AudioQueueBufferRef buffers[kNumberBuffers];
    AudioStreamBasicDescription format;
    memset(&format, 0, sizeof(format));
    format.mSampleRate          = 44100;
    format.mFormatID            = kAudioFormatLinearPCM;
    format.mFormatFlags         = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
    format.mChannelsPerFrame    = 1;
    format.mBitsPerChannel      = 16;
    format.mBytesPerFrame       = (format.mBitsPerChannel / 8) * format.mChannelsPerFrame;
    format.mFramesPerPacket     = 1;
    format.mBytesPerPacket      = format.mBytesPerFrame * format.mFramesPerPacket;

    AudioQueueNewOutput(&format, 
                        AQOutputCallback, 
                        self,
                        CFRunLoopGetCurrent(), 
                        kCFRunLoopCommonModes, 
                        0, 
                        &audioQueue);

    // allocate and fill the buffers
    for (int i = 0; i < kNumberBuffers; ++i)
    {
        AudioQueueAllocateBuffer(audioQueue, kBufferSize, &buffers[i]);
        AQOutputCallback(self, audioQueue, buffers[i]);
    }

    AudioQueueSetParameter(audioQueue, kAudioQueueParam_Volume, 1.0);
    AudioQueueStart(audioQueue, NULL);
}

- (void)handleBufferCompleteForQueue:(AudioQueueRef)inAQ
                              buffer:(AudioQueueBufferRef)inBuffer
{
    inBuffer->mAudioDataByteSize = inBuffer->mAudioDataBytesCapacity; 

    int *buffer = (int *)inBuffer->mAudioData;
    for (int i = 0; i < inBuffer->mAudioDataByteSize/sizeof(int); ++i)
    {
        buffer[i] = (int)rand(); // refill the buffer
    }
    AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL);
}
// END STATIC ADDITIONS

@end

一旦我弄清楚如何实际重新填充缓冲区(inBuffer->mAudioData 使用某种类型转换)，其他一切就都到位了。