Question

我已经搜索并且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，没有任何反应。以下是核心代码：

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应用之间的区别就是它。在OS X中：

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并在iOS中正确播放MIDI音符？我对Audio Unit / AUGraph ...

没有明确或深刻的理解

更新：添加cd.componentSubType = kAudioUnitSubType_RemoteIO;时使用outNode将是正确的，并成功播放柔和的MIDI音符。

Answer 1

kAudioUnitSubType_GenericOutput应为kAudioUnitSubType_RemoteIO 对于iOS。

你需要让图表运行才能播放音频，所以不要立即调用AUGraphStop（）和DisposeAUGraph（）。

为了测试图形，我会使用kAudioUnitSubType_Sampler而不是kAudioUnitSubType_MIDISynth，因为如果你没有设置它的预设，它会有一个内置的波形发生器。然后当你使图表工作时，试试你的合成器。

Answer 2

将AVFoundation和AudioToolbox框架链接到您的项目，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);

iOS怎么玩midi笔记？

2 个答案: