考虑您自己的 midi 客户端创建应用程序可能会崩溃，或者发送 midi 的主机也可能崩溃。您可以通过检查客户端/目的地是否已经存在然后通过处理单例分配来更轻松地处理这个问题。当您的 Midi 客户端存在但无法正常工作时，这是因为您需要告诉 CoreMidi 您的服装制作客户端能够处理什么以及当主机发送客户端大量使用时间戳时它将有什么延迟（又名ableton 和其他） .
在您的 .h 文件中
#import <CoreMIDI/CoreMIDI.h>
#import <CoreAudio/HostTime.h>
@interface YourVirtualMidiHandlerObject : NSObject
@property (assign, nonatomic) MIDIClientRef midi_client;
@property (nonatomic) MIDIEndpointRef outSrc;
@property (nonatomic) MIDIEndpointRef inSrc;
- (id)initWithVirtualSourceName:(NSString *)clientName;
@end
在您的 .m 文件中
@interface YourVirtualMidiHandlerObject () {
MIDITimeStamp midiTime;
MIDIPacketList pktList;
}
@end
您可以通过以下方式准备启动您的虚拟客户端
也在你的 .m 文件中
@implementation YourVirtualMidiHandlerObject
// this you can call in dealloc or manually
// else where when you stop working with your virtual client
-(void)teardown {
MIDIEndpointDispose(_inSrc);
MIDIEndpointDispose(_outSrc);
MIDIClientDispose(_midi_client);
}
- (id)initWithVirtualSourceName:(NSString *)clientName {
if (self = [super init]) {
OSStatus status = MIDIClientCreate((__bridge CFStringRef)clientName, (MIDINotifyProc)MidiNotifyProc, (__bridge void *)(self), &_midi_client);
BOOL isSourceLoaded = NO;
BOOL isDestinationLoaded = NO;
ItemCount sourceCount = MIDIGetNumberOfSources();
for (ItemCount i = 0; i < sourceCount; ++i) {
_outSrc = MIDIGetSource(i);
if ( _outSrc != 0 ) {
if ([[self getMidiDisplayName:_outSrc] isEqualToString:clientName] && !isSourceLoaded) {
isSourceLoaded = YES;
break; //stop looping thru sources if it is existing
}
}
}
ItemCount destinationCount = MIDIGetNumberOfDestinations();
for (ItemCount i = 0; i < destinationCount; ++i) {
_inSrc = MIDIGetDestination(i);
if (_inSrc != 0) {
if ([[self getMidiDisplayName:_inSrc] isEqualToString:clientName] && !isDestinationLoaded) {
isDestinationLoaded = YES;
break; //stop looping thru destinations if it is existing
}
}
}
if(!isSourceLoaded) {
//your costume source needs to tell CoreMidi what it is handling
MIDISourceCreate(_midi_client, (__bridge CFStringRef)clientName, &_outSrc);
MIDIObjectSetIntegerProperty(_outSrc, kMIDIPropertyMaxTransmitChannels, 16);
MIDIObjectSetIntegerProperty(_outSrc, kMIDIPropertyTransmitsProgramChanges, 1);
MIDIObjectSetIntegerProperty(_outSrc, kMIDIPropertyTransmitsNotes, 1);
// MIDIObjectSetIntegerProperty(_outSrc, kMIDIPropertyTransmitsClock, 1);
isSourceLoaded = YES;
}
if(!isDestinationLoaded) {
//your costume destination needs to tell CoreMidi what it is handling
MIDIDestinationCreate(_midi_client, (__bridge CFStringRef)clientName, midiRead, (__bridge void *)(self), &_inSrc);
MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyAdvanceScheduleTimeMuSec, 1); // consider more 14ms in some cases
MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesClock, 1);
MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesNotes, 1);
MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesProgramChanges, 1);
MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyMaxReceiveChannels, 16);
// MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesMTC, 1);
// MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesBankSelectMSB, 1);
// MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertyReceivesBankSelectLSB, 1);
// MIDIObjectSetIntegerProperty(_inSrc, kMIDIPropertySupportsMMC, 1);
isDestinationLoaded = YES;
}
if (!isDestinationLoaded || !isSourceLoaded) {
if (status != noErr ) {
NSLog(@"Failed creation of virtual Midi client \"%@\", so disposing the client!",clientName);
MIDIClientDispose(_midi_client);
}
}
}
return self;
}
// Returns the display name of a given MIDIObjectRef as an NSString
-(NSString *)getMidiDisplayName:(MIDIObjectRef)obj {
CFStringRef name = nil;
if (noErr != MIDIObjectGetStringProperty(obj, kMIDIPropertyDisplayName, &name)) return nil;
return (__bridge NSString *)name;
}
对于那些试图在创建过程中读取速度（midi 传输）并为虚拟目的地设置属性的人...
不要忘记时间戳随数据包一起发送，但一个数据包可以包含多个相同类型的命令，甚至是多个时钟命令。在构建时钟计数器以查找 bpm 速度时，您必须考虑在计算之前至少计算其中的 12 个。当您只使用其中 3 个时，您实际上是在测量自己的缓冲区读取处理延迟，而不是真正的时间戳。
如果 midi 发件人未能正确设置时间戳，您的读取过程（回调）将处理时间戳...
void midiRead(const MIDIPacketList * pktlist, void * readProcRefCon, void * srcConnRefCon) {
const MIDIPacket *pkt = pktlist->packet;
for ( int index = 0; index < pktlist->numPackets; index++, pkt = MIDIPacketNext(pkt) ) {
MIDITimeStamp timestamp = pkt->timeStamp;
if ( !timestamp ) timestamp = mach_absolute_time();
if ( pkt->length == 0 ) continue;
const Byte *p = &pkt->data[0];
Byte functionalDataGroup = *p & 0xF0;
// Analyse the buffered bytes in functional groups is faster
// like 0xF will tell it is clock/transport midi stuff
// go in detail after this will shorten the processing
// and it is easier to read in code
switch (functionalDataGroup) {
case 0xF : {
// in here read the exact Clock command
// 0xF8 = clock
}
break;
case ... : {
// do other nice grouped stuff here, like reading notes
}
break;
default : break;
}
}
}
不要忘记客户端需要一个回调来处理内部通知。
void MidiNotifyProc(const MIDINotification* message, void* refCon) {
// when creation of virtual client fails we despose the whole client
// meaning unless you need it you can ignore added/removed notifications
if (message->messageID != kMIDIMsgObjectAdded &&
message->messageID != kMIDIMsgObjectRemoved) return;
// reactions to other midi notications you gonna trigger here..
}
然后你可以发送midi ...
-(void)sendMIDICC:(uint8_t)cc Value:(uint8_t)v ChZeroToFifteen:(uint8_t)ch {
MIDIPacket *packet = MIDIPacketListInit(&pktList);
midiTime = packet->timeStamp;
unsigned char ctrl[3] = { 0xB0 + ch, cc, v };
while (1) {
packet = MIDIPacketListAdd(&pktList, sizeof(pktList), packet, midiTime, sizeof(ctrl), ctrl);
if (packet != NULL) break;
// create an extra packet to fill when it failed before
packet = MIDIPacketListInit(&pktList);
}
// OSStatus check = // you dont need it if you don't check failing
MIDIReceived(_outSrc, &pktList);
}