小贝子编程

AVAudioPCMBuffer用于音乐文件



我一直在尝试在我的SpriteKit游戏中播放音乐，并使用AVAudioPlayerNode类通过AVAudioPCMBuffer s来做到这一点。每次我导出我的OS X项目时，它都会崩溃并给我一个关于音频播放的错误。在过去的24小时里，我的头一直在墙上撞，我决定重新观看WWDC 501会议。我对这个问题的解决方案是演示者使用的，即将缓冲区的帧分解成更小的片段，以分解正在读取的音频文件。

NSError *error = nil;
NSURL *someFileURL = ...
AVAudioFile *audioFile = [[AVAudioFile alloc] initForReading: someFileURL commonFormat: AVAudioPCMFormatFloat32 interleaved: NO error:&error];
const AVAudioFrameCount kBufferFrameCapacity = 128 * 1024L;
AVAudioFramePosition fileLength = audioFile.length;
AVAudioPCMBuffer *readBuffer = [[AvAudioPCMBuffer alloc] initWithPCMFormat: audioFile.processingFormat frameCapacity: kBufferFrameCapacity];
while (audioFile.framePosition < fileLength) {
    AVAudioFramePosition readPosition = audioFile.framePosition;
    if (![audioFile readIntoBuffer: readBuffer error: &error])
        return NO;
    if (readBuffer.frameLength == 0) //end of file reached
        break;
}

我目前的问题是，播放器只播放最后一帧读取到缓冲区。我演奏的音乐只有两分钟长。显然，这太长了，不能直接读入缓冲区。是缓冲区被覆盖每次readIntoBuffer:方法被称为循环内?我在这方面是个新手……我怎样才能播放整个文件?

如果我不能得到这个工作，什么是跨多个SKScene s播放音乐(2个不同的文件)的好方法?

这是我想到的解决方案。它仍然不完美，但希望它能帮助那些和我有同样困境的人。我创建了一个单例类来处理这项工作。未来可以做的一个改进是只在需要的时候加载特定SKScene所需的声音效果和音乐文件。我在这段代码中遇到了很多问题，我现在不想弄乱它。目前，我没有太多的声音，所以它不会占用过多的内存。


我的策略如下:

  1. 将游戏的音频文件名存储在plist中
  2. 从plist中读取并创建两个字典(一个用于音乐，一个用于短声音效果)

    3. 声音效果字典由AVAudioPCMBuffer和AVAudioPlayerNode组成

  3. 音乐字典是由AVAudioPCMBuffers数组、AVAudioPlayerNode和原始音频文件的采样率组成的

    • 采样率对于计算每个缓冲区应该播放的时间是必要的(您将看到在代码中完成的计算)

  4. 创建一个AVAudioEngine并从引擎中获取主混音器，并将所有AVAudioPlayerNodes附加到混音器(如往常一样)

  5. 使用各种方法播放声音效果或音乐
    • 音效播放是直截了当的…调用方法-(void) playSfxFile:(NSString*)file;然后播放声音
    • 对于音乐，我只是找不到一个好的解决方案，而不是调用场景的帮助来播放音乐。场景将调用-(void) playMusicFile:(NSString*)file;，它将按照创建缓冲区的顺序安排缓冲区的播放。我找不到一个好方法来让音乐在我的AudioEngine类中重复一次完成，所以我决定让场景检查它的update:方法是否为特定文件播放音乐，如果不是，再次播放它(不是一个非常光滑的解决方案，但它有效)

AudioEngine.h 

#import <Foundation/Foundation.h>
@interface AudioEngine : NSObject
+(instancetype)sharedData;
-(void) playSfxFile:(NSString*)file;
-(void) playMusicFile:(NSString*)file;
-(void) pauseMusic:(NSString*)file;
-(void) unpauseMusic:(NSString*)file;
-(void) stopMusicFile:(NSString*)file;
-(void) setVolumePercentages;
-(bool) isPlayingMusic:(NSString*)file;
@end

)。m 

#import "AudioEngine.h"
#import <AVFoundation/AVFoundation.h>
#import "GameData.h" //this is a class that I use to store game data (in this case it is being used to get the user preference for volume amount)
@interface AudioEngine()
@property AVAudioEngine *engine;
@property AVAudioMixerNode *mixer;
@property NSMutableDictionary *musicDict;
@property NSMutableDictionary *sfxDict;
@property NSString *audioInfoPList;
@property float musicVolumePercent;
@property float sfxVolumePercent;
@property float fadeVolume;
@property float timerCount;
@end
@implementation AudioEngine
int const FADE_ITERATIONS = 10;
static NSString * const MUSIC_PLAYER = @"player";
static NSString * const MUSIC_BUFFERS = @"buffers";
static NSString * const MUSIC_FRAME_POSITIONS = @"framePositions";
static NSString * const MUSIC_SAMPLE_RATE = @"sampleRate";
static NSString * const SFX_BUFFER = @"buffer";
static NSString * const SFX_PLAYER = @"player";
+(instancetype) sharedData {
    static AudioEngine *sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] init];
        [sharedInstance startEngine];
    });
    return sharedInstance;
}
-(instancetype) init {
    if (self = [super init]) {
        _engine = [[AVAudioEngine alloc] init];
        _mixer = [_engine mainMixerNode];
        _audioInfoPList = [[NSBundle mainBundle] pathForResource:@"AudioInfo" ofType:@"plist"]; //open a plist called AudioInfo.plist
        [self setVolumePercentages]; //this is created to set the user's preference in terms of how loud sound fx and music should be played
        [self initMusic];
        [self initSfx];
    }
    return self;
}
//opens all music files, creates multiple buffers depending on the length of the file and a player
-(void) initMusic {
    _musicDict = [NSMutableDictionary dictionary];
    _audioInfoPList = [[NSBundle mainBundle] pathForResource: @"AudioInfo" ofType: @"plist"];
    NSDictionary *audioInfoData = [NSDictionary dictionaryWithContentsOfFile:_audioInfoPList];
    for (NSString *musicFileName in audioInfoData[@"music"]) {
        [self loadMusicIntoBuffer:musicFileName];
        AVAudioPlayerNode *player = [[AVAudioPlayerNode alloc] init];
        [_engine attachNode:player];
        AVAudioPCMBuffer *buffer = [[_musicDict[musicFileName] objectForKey:MUSIC_BUFFERS] objectAtIndex:0];
        [_engine connect:player to:_mixer format:buffer.format];
        [_musicDict[musicFileName] setObject:player forKey:@"player"];
    }
}
//opens a music file and creates an array of buffers
-(void) loadMusicIntoBuffer:(NSString *)filename
{
    NSURL *audioFileURL = [[NSBundle mainBundle] URLForResource:filename withExtension:@"aif"];
    //NSURL *audioFileURL = [NSURL URLWithString:[[NSBundle mainBundle] pathForResource:filename ofType:@"aif"]];
    NSAssert(audioFileURL, @"Error creating URL to audio file");
    NSError *error = nil;
    AVAudioFile *audioFile = [[AVAudioFile alloc] initForReading:audioFileURL commonFormat:AVAudioPCMFormatFloat32 interleaved:NO error:&error];
    NSAssert(audioFile != nil, @"Error creating audioFile, %@", error.localizedDescription);
    AVAudioFramePosition fileLength = audioFile.length; //frame length of the audio file
    float sampleRate = audioFile.fileFormat.sampleRate; //sample rate (in Hz) of the audio file
    [_musicDict setObject:[NSMutableDictionary dictionary] forKey:filename];
    [_musicDict[filename] setObject:[NSNumber numberWithDouble:sampleRate] forKey:MUSIC_SAMPLE_RATE];
    NSMutableArray *buffers = [NSMutableArray array];
    NSMutableArray *framePositions = [NSMutableArray array];
    const AVAudioFrameCount kBufferFrameCapacity = 1024 * 1024L; //the size of my buffer...can be made bigger or smaller 512 * 1024L would be half the size
    while (audioFile.framePosition < fileLength) { //each iteration reads in kBufferFrameCapacity frames of the audio file and stores it in a buffer
        [framePositions addObject:[NSNumber numberWithLongLong:audioFile.framePosition]];
        AVAudioPCMBuffer *readBuffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:audioFile.processingFormat frameCapacity:kBufferFrameCapacity];
        if (![audioFile readIntoBuffer:readBuffer error:&error]) {
            NSLog(@"failed to read audio file: %@", error);
            return;
        }
        if (readBuffer.frameLength == 0) { //if we've come to the end of the file, end the loop
            break;
        }
        [buffers addObject:readBuffer];
    }
    [_musicDict[filename] setObject:buffers forKey:MUSIC_BUFFERS];
    [_musicDict[filename] setObject:framePositions forKey:MUSIC_FRAME_POSITIONS];
}
-(void) initSfx {
    _sfxDict = [NSMutableDictionary dictionary];
    NSDictionary *audioInfoData = [NSDictionary dictionaryWithContentsOfFile:_audioInfoPList];
    for (NSString *sfxFileName in audioInfoData[@"sfx"]) {
        AVAudioPlayerNode *player = [[AVAudioPlayerNode alloc] init];
        [_engine attachNode:player];
        [self loadSoundIntoBuffer:sfxFileName];
        AVAudioPCMBuffer *buffer = [_sfxDict[sfxFileName] objectForKey:SFX_BUFFER];
        [_engine connect:player to:_mixer format:buffer.format];
        [_sfxDict[sfxFileName] setObject:player forKey:SFX_PLAYER];
    }
}
//WARNING: make sure that the sound fx file is small (roughly under 30 sec) otherwise the archived version of the app will crash because the buffer ran out of space
-(void) loadSoundIntoBuffer:(NSString *)filename
{
    NSURL *audioFileURL = [NSURL URLWithString:[[NSBundle mainBundle] pathForResource:filename ofType:@"mp3"]];
    NSAssert(audioFileURL, @"Error creating URL to audio file");
    NSError *error = nil;
    AVAudioFile *audioFile = [[AVAudioFile alloc] initForReading:audioFileURL commonFormat:AVAudioPCMFormatFloat32 interleaved:NO error:&error];
    NSAssert(audioFile != nil, @"Error creating audioFile, %@", error.localizedDescription);
    AVAudioPCMBuffer *readBuffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:audioFile.processingFormat frameCapacity:(AVAudioFrameCount)audioFile.length];
    [audioFile readIntoBuffer:readBuffer error:&error];
    [_sfxDict setObject:[NSMutableDictionary dictionary] forKey:filename];
    [_sfxDict[filename] setObject:readBuffer forKey:SFX_BUFFER];
}
-(void)startEngine {
    [_engine startAndReturnError:nil];
}
-(void) playSfxFile:(NSString*)file {
    AVAudioPlayerNode *player = [_sfxDict[file] objectForKey:@"player"];
    AVAudioPCMBuffer *buffer = [_sfxDict[file] objectForKey:SFX_BUFFER];
    [player scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferInterrupts completionHandler:nil];
    [player setVolume:1.0];
    [player setVolume:_sfxVolumePercent];
    [player play];
}
-(void) playMusicFile:(NSString*)file {
    AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
    if ([player isPlaying] == NO) {
        NSArray *buffers = [_musicDict[file] objectForKey:MUSIC_BUFFERS];
        double sampleRate = [[_musicDict[file] objectForKey:MUSIC_SAMPLE_RATE] doubleValue];

        for (int i = 0; i < [buffers count]; i++) {
            long long framePosition = [[[_musicDict[file] objectForKey:MUSIC_FRAME_POSITIONS] objectAtIndex:i] longLongValue];
            AVAudioTime *time = [AVAudioTime timeWithSampleTime:framePosition atRate:sampleRate];
            AVAudioPCMBuffer *buffer  = [buffers objectAtIndex:i];
            [player scheduleBuffer:buffer atTime:time options:AVAudioPlayerNodeBufferInterrupts completionHandler:^{
                if (i == [buffers count] - 1) {
                    [player stop];
                }
            }];
            [player setVolume:_musicVolumePercent];
            [player play];
        }
    }
}
-(void) stopOtherMusicPlayersNotNamed:(NSString*)file {
    if ([file isEqualToString:@"menuscenemusic"]) {
        AVAudioPlayerNode *player = [_musicDict[@"levelscenemusic"] objectForKey:MUSIC_PLAYER];
        [player stop];
    }
    else {
        AVAudioPlayerNode *player = [_musicDict[@"menuscenemusic"] objectForKey:MUSIC_PLAYER];
        [player stop];
    }
}
//stops the player for a particular sound
-(void) stopMusicFile:(NSString*)file {
    AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
    if ([player isPlaying]) {
        _timerCount = FADE_ITERATIONS;
        _fadeVolume = _musicVolumePercent;
        [self fadeOutMusicForPlayer:player]; //fade out the music
    }
}
//helper method for stopMusicFile:
-(void) fadeOutMusicForPlayer:(AVAudioPlayerNode*)player {
    [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(handleTimer:) userInfo:player repeats:YES];
}
//helper method for stopMusicFile:
-(void) handleTimer:(NSTimer*)timer {
    AVAudioPlayerNode *player = (AVAudioPlayerNode*)timer.userInfo;
    if (_timerCount > 0) {
        _timerCount--;
        AVAudioPlayerNode *player = (AVAudioPlayerNode*)timer.userInfo;
        _fadeVolume = _musicVolumePercent * (_timerCount / FADE_ITERATIONS);
        [player setVolume:_fadeVolume];
    }
    else {
        [player stop];
        [player setVolume:_musicVolumePercent];
        [timer invalidate];
    }
}
-(void) pauseMusic:(NSString*)file {
    AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
    if ([player isPlaying]) {
        [player pause];
    }
}
-(void) unpauseMusic:(NSString*)file {
    AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
    [player play];
}
//sets the volume of the player based on user preferences in GameData class
-(void) setVolumePercentages {
    NSString *musicVolumeString = [[GameData sharedGameData].settings objectForKey:@"musicVolume"];
    _musicVolumePercent = [[[musicVolumeString componentsSeparatedByCharactersInSet:
    [[NSCharacterSet decimalDigitCharacterSet] invertedSet]]
    componentsJoinedByString:@""] floatValue] / 100;
    NSString *sfxVolumeString = [[GameData sharedGameData].settings objectForKey:@"sfxVolume"];
    _sfxVolumePercent = [[[sfxVolumeString componentsSeparatedByCharactersInSet:
    [[NSCharacterSet decimalDigitCharacterSet] invertedSet]]
    componentsJoinedByString:@""] floatValue] / 100;
    //immediately sets music to new volume
    for (NSString *file in [_musicDict allKeys]) {
        AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
        [player setVolume:_musicVolumePercent];
    }
}
-(bool) isPlayingMusic:(NSString *)file {
    AVAudioPlayerNode *player = [_musicDict[file] objectForKey:MUSIC_PLAYER];
    if ([player isPlaying])
        return YES;
    return NO;
}
@end

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