我不清楚时间戳字段是否可用于在将来安排MIDI事件，即在调用MIDISend之后发生。以下代码尝试每秒安排10个音符和10个音符关闭。时间戳应该指定音符的音符在音符开启后1/10秒发生，但是在我尝试过的所有硬件或虚拟目的地上，似乎所有事件都在调用MIDISend时立即发送。这是一般行为还是某些MIDI硬件/某些虚拟MIDI目的地是否支持使用时间戳值正确调度事件？这是我的代码：
/* send_midi_port.c
* Open connection with destination (rather than setting up MIDI source) and send
* timestamped messages
*/
#include <stdlib.h>
#include <stdio.h>
#include <CoreMIDI.h>
#include <HostTime.h>
#include <string.h>
#include <CoreServices/CoreServices.h>
#include <mach/mach.h>
#include <mach/mach_time.h>
#include <unistd.h>
#define STR_BUFSIZE 200
#define ERR_EXIT(x)\
fprintf(stderr,"Error %s\n",x);\
return -1;
typedef void (*sig_t) (int);
static volatile int done = 0;
static mach_timebase_info_data_t sTimebaseInfo;
void int_handle(int signum)
{
done = 1;
}
char *CFString_strncpy(char *dest,
CFStringRef str,
size_t n)
{
CFStringEncoding encoding = kCFStringEncodingUTF8;
if (!CFStringGetCString(str, dest, n, encoding)) {
dest = NULL;
}
return dest;
}
int CFString_cstr_strncmp(CFStringRef s1, char *s2, size_t n)
{
char buf[STR_BUFSIZE];
if (CFString_strncpy(buf, s1, STR_BUFSIZE) == NULL) {
return -2;
}
return strncmp(buf,s2,n);
}
/* Print CFString to stdout */
void CFString_printf(CFStringRef str)
{
char buffer[STR_BUFSIZE];
CFStringEncoding encoding = kCFStringEncodingUTF8;
const char *ptr = CFStringGetCStringPtr(str, encoding);
if (ptr == NULL) {
if (CFStringGetCString(str, buffer, STR_BUFSIZE, encoding)) {
ptr = buffer;
}
}
if (ptr) {
printf("%s",ptr);
}
}
/* Get MIDI object's name as CFStringRef */
CFStringRef MIDIObjectRef_get_name(MIDIObjectRef obj)
{
CFStringRef name = NULL;
OSStatus err;
err = MIDIObjectGetStringProperty(obj,kMIDIPropertyName,&name);
if (err) {
return NULL;
}
return name;
}
UInt64 nano_to_absolute(UInt64 nano)
{
return nano * sTimebaseInfo.denom / sTimebaseInfo.numer;
}
int main(int argc, char **argv)
{
// Get Timebase info
(void) mach_timebase_info(&sTimebaseInfo);
char desired_dest_[] = "FastTrack Pro";
char *desired_dest;
if (argc < 2) {
printf("No device specified, using default output %s.\n", desired_dest_);
desired_dest = desired_dest_;
} else {
desired_dest = argv[1];
}
ItemCount n_dests = MIDIGetNumberOfDestinations();
int found = 0;
MIDIEndpointRef desired_epr;
while (n_dests--) {
MIDIEndpointRef dest = MIDIGetDestination(n_dests);
CFStringRef name = MIDIObjectRef_get_name(dest);
if (CFString_cstr_strncmp(name,desired_dest,strlen(desired_dest))
== 0) {
printf(" Name of destination %d: ",(int)n_dests);
CFString_printf(name);
printf("\n");
found = 1;
desired_epr = dest;
}
}
if (!found) {
printf("Destination %s not found.\n",desired_dest);
return -1;
}
OSStatus result;
MIDIClientRef clientref;
result = MIDIClientCreate(CFSTR("default"),NULL,NULL,&clientref);
if (result < 0 ) {
ERR_EXIT("Creating client.");
}
MIDIPortRef portref;
result = MIDIOutputPortCreate(clientref,CFSTR("hiports"),&portref);
if (result < 0 ) {
ERR_EXIT("Creating port.");
}
signal(SIGINT,int_handle);
while (!done) {
// With multiple and time stamps
ByteCount mpdsize = sizeof(MIDIPacketList)+sizeof(MIDIPacket)*20;
char mpdata[mpdsize];
memset(mpdata,0,mpdsize);
MIDIPacketList *midipackets;
midipackets = (MIDIPacketList*)mpdata;
MIDIPacket *mp;
mp = MIDIPacketListInit(midipackets);
int n;
UInt64 timeNano, timeScale;
for (n = 0; n < 20; n += 2) {
Byte noteOnData[3] = {0x90,60+(n/2),100};
Byte noteOffData[3] = {0x80,60+(n/2),0};
// on all the devices I tried, the timestamps seem to be ignored
mp = MIDIPacketListAdd(midipackets,mpdsize,mp,
nano_to_absolute(((UInt64)n/2) * 100ULL * 1000ULL * 1000ULL),
// seems equivalent to 0
// 0,
3,noteOnData);
if (!mp) {
ERR_EXIT("Adding MIDI packet.\n");
}
mp = MIDIPacketListAdd(midipackets,mpdsize,mp,
nano_to_absolute((((UInt64)n/2)+1) * 100ULL * 1000ULL * 1000ULL),
// seems equivalent to 0
// 0,
3,noteOffData);
if (!mp) {
ERR_EXIT("Adding MIDI packet.\n");
}
}
// Check packets
printf("Number of packets: %d\n",(int)midipackets->numPackets);
MIDIPacket *__p = &midipackets->packet[0];
int i;
for (i = 0; i < midipackets->numPackets; ++i) {
printf("Timestamp: %llu\n"
"Length: %d\n"
"Data : ",
__p->timeStamp,
(int)__p->length);
int j;
for (j = 0; j < __p->length; j++) {
printf("%d ",(int)__p->data[j]);
}
printf("\n");
__p = MIDIPacketNext(__p);
}
printf("Sending notes\n");
MIDISend(portref,desired_epr,midipackets);
sleep(1);
}
MIDIPortDispose(portref);
MIDIClientDispose(clientref);
return 0;
}
这可以使用命令构建（框架的路径可能在您的计算机上有所不同）
clang send_midi_port.c -o send_midi_port.bin - I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/CoreMIDI.framework/Headers -framework CoreMIDI -g -framework CoreFoundation -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/CoreAudio.framework/Headers -framework CoreAudio -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/CoreServices.framework/Headers -framework CoreServices
答案 0 :(得分：0)
当您致电MIDIPacketListAdd时，您没有提供正确的时间戳。您传递的是当前时间的偏移量，从第一个事件的0开始，随后的事件增加。但是你不包括现在的时间。
因此，CoreMIDI认为时间戳是过去的，所以它会立即发送事件。
使用AudioGetCurrentHostTime获取当前时间，并将每个偏移量添加到该时间。
UInt64 now = AudioGetCurrentHostTime();
for (n = 0; n < 20; n += 2) {
Byte noteOnData[3] = {0x90,60+(n/2),100};
Byte noteOffData[3] = {0x80,60+(n/2),0};
mp = MIDIPacketListAdd(midipackets,mpdsize,mp,
now + nano_to_absolute(((UInt64)n/2) * 100ULL * 1000ULL * 1000ULL),
3,noteOnData);
mp = MIDIPacketListAdd(midipackets,mpdsize,mp,
now + nano_to_absolute((((UInt64)n/2)+1) * 100ULL * 1000ULL * 1000ULL),
3,noteOffData);
}
当您使用MIDISend时，CoreMIDI将处理调度，无论终端设备是MIDI硬件还是其他应用程序拥有的虚拟MIDI目标。