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来完成。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，我的头靠在墙上后，我决定重新观看WWDC session 501（见54:17）。我解决这个问题的方法是演示者使用的方法，即将缓冲区的帧分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读入缓冲区的最后一帧。我正在播放的音乐只有2分钟。显然，这太长了，不能直接读入缓冲区。每次在循环内调用readIntoBuffer:方法时，缓冲区是否被覆盖？我就是这样的菜鸟......我怎样才能播放整个文件？
如果我无法使用此功能，那么在多个SKScene中播放音乐（2个不同的文件）的好方法是什么？
答案 0 :(得分：2)
这是我提出的解决方案。它仍然不完美，但希望它能帮助那些处于我所处的困境中的人。我创建了一个单身人士班来处理这项工作。可以在将来进行的一项改进是仅在需要时加载特定SKScene所需的声音效果和音乐文件。我对这段代码有很多问题，我现在不想搞砸它。目前，我没有太多的声音，所以它没有使用过多的内存。
<强>概述
我的策略如下：
音乐词典由AVAudioPCMBuffers数组组成，这是一个时间戳数组，用于何时应该在队列中播放这些缓冲区，AVAudioPlayerNode和原始音频文件的采样率
创建AVAudioEngine并从引擎获取主混音器并将所有AVAudioPlayerNodes连接到调音台（按照惯例）
-(void) playSfxFile:(NSString*)file;
它发出声音-(void) playMusicFile:(NSString*)file;，它将调度缓冲区以便创建它们。在AudioEngine课程中完成后，我无法找到一种让音乐重复的好方法，因此我决定让场景检查其update:方法音乐是否正在播放对于特定文件，如果没有，再次播放（不是一个非常光滑的解决方案，但它的工作原理） 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
AudioEngine.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