iOS如何播放midi音符？

Question

我已经搜索并已经完成了可以播放MIDI音符的OS X应用程序，但是当我在iOS中尝试时，没有任何事情发生。这里是核心代码：

AUGraph graph; 
AudioUnit synthUnit; 
AUNode synthNode, outNode; 

NewAUGraph(&graph); 

AudioComponentDescription cd; 
cd.componentManufacturer = kAudioUnitManufacturer_Apple; 

cd.componentType = kAudioUnitType_MusicDevice; 
cd.componentSubType = kAudioUnitSubType_MIDISynth; 
AUGraphAddNode(graph, &cd, &synthNode); 

cd.componentType = kAudioUnitType_Output; 
cd.componentSubType = kAudioUnitSubType_GenericOutput; 
AUGraphAddNode(graph, &cd, &outNode), "AUGraphAddNode"); 

CheckError(AUGraphOpen(graph), "AUGraphOpen"); 

AUGraphConnectNodeInput(graph, synthNode, 0, outNode, 0); 

AUGraphNodeInfo(graph, synthNode, 0, &synthUnit); 

AUGraphInitialize(graph); 
CAShow(graph); 

AUGraphStart(graph); 

CFURLRef bankURL = ... //gs_instruments.dls 
AudioUnitSetProperty(synthUnit, 
        kMusicDeviceProperty_SoundBankURL, 
        kAudioUnitScope_Global, 
        0, 
        &bankURL, 
        sizeof(bankURL)); 

static UInt32 kChannelMessage_NoteOn = 0x90; 
UInt8 channel = 0; 
UInt8 note = 60; 
UInt32 velocity = 127; 

MusicDeviceMIDIEvent(synthUnit, 
        kChannelMessage_NoteOn | channel, 
        note, 
        velocity, 
        0); 

AUGraphStop(graph); 
DisposeAUGraph(graph); 

我知道cd.componentType和cd.componentSubType设置可能不正确，因为iOS应用和OS X应用程序之间的区别只是它。在OS X：

AudioComponentDescription cd; 
cd.componentManufacturer = kAudioUnitManufacturer_Apple; 

cd.componentType = kAudioUnitType_MusicDevice; 
cd.componentSubType = kAudioUnitSubType_DLSSynth; 
AUGraphAddNode(graph, &cd, &synthNode); 

cd.componentType = kAudioUnitType_Output; 
cd.componentSubType = kAudioUnitSubType_DefaultOutput; 
AUGraphAddNode(graph, &cd, &outNode); 

如何设置cd和iOS的正常播放MIDI音符？我没有明确或Audio Unit/AUGraph更深刻的了解...

更新：使用cd.componentSubType = kAudioUnitSubType_RemoteIO;当添加outNode将是正确的和打软MIDI成功地指出。

Answer 1

kAudioUnitSubType_GenericOutput应该kAudioUnitSubType_RemoteIO 为iOS。

您需要让图表运行以播放音频，因此不要立即调用AUGraphStop（）和DisposeAUGraph（）。

为了测试图形，我会使用kAudioUnitSubType_Sampler而不是kAudioUnitSubType_MIDISynth，因为如果您没有设置它的预设，它会有一个内置的波形发生器。然后，当你得到图表的工作，试试你的合成器。

Answer 2

链接AVFoundation，并AudioToolbox框架到您的项目，然后使用此代码：

#import <AVFoundation/AVFoundation.h> 

NSURL *midiUrl = [[NSBundle mainBundle] URLForResource:@"even voor mij" withExtension:@"mid"]; 

MusicPlayer player = NULL; 

NewMusicPlayer(&player); 

MusicSequence sequence = NULL; 

NewMusicSequence(&sequence); 

MusicSequenceFileLoad(sequence, (__bridge CFURLRef)midiUrl, NULL, NULL); 

MusicPlayerSetSequence(player, sequence); 

MusicPlayerStart(player);