IOS How record midi file with Midi input callback? - ios

Question

I try to record midi file with an Ipad.
My Ipad is pluged with the usb output of my electric piano.
I have read the apple core midi documentation and I have understand that :
For record a file, I should create a MusicSequence. So that I try to do but It doesn't work :(
Here is my code:
Firstly, I setup my midi connection:
-(void) setupMIDI {
MIDIClientRef client = nil;
MIDIClientCreate(CFSTR("Core MIDI to System Sounds Demo"), MyMIDINotifyProc, (__bridge void *)(self), &client);
inputPort = nil;
MIDIInputPortCreate(client, CFSTR("Input port"), MyMIDIReadProc, (__bridge void *)(self), &inputPort);
sequence = nil;
NewMusicSequence(&(sequence));
unsigned long sourceCount = MIDIGetNumberOfSources();
[self appendToTextView:[NSString stringWithFormat:#"%ld sources\n", sourceCount]];
for (int i = 0; i < sourceCount; ++i) {
MIDIEndpointRef src = MIDIGetSource(i);
CFStringRef endpointName = NULL;
OSStatus nameErr = MIDIObjectGetStringProperty(src, kMIDIPropertyName, &endpointName);
if (noErr == nameErr) {
[self appendToTextView: [NSString stringWithFormat:#" source %d: %#\n", i, endpointName]];
}
MIDIPortConnectSource(inputPort, src, NULL);
MusicSequenceSetMIDIEndpoint(sequence, src);
}
}
After that, I receive my Midi event with MyMIDIReadProc which is a callback function of my input port :
static void MyMIDIReadProc(const MIDIPacketList *pktlist, void *refCon, void *connRefCon)
{
AppViewController *vc = (__bridge AppViewController*) refCon;
MIDIPacket *packet = (MIDIPacket *)pktlist->packet;
for (int i=0; i < pktlist->numPackets; i++) {
Byte midiStatus = packet->data[0];
Byte midiCommand = midiStatus >> 4;
// is it a note-on or note-off
if ((midiCommand == 0x09) ||
(midiCommand == 0x08)) {
Byte note = packet->data[1] & 0x7F;
Byte velocity = packet->data[2] & 0x7F;
NSLog(#"midiCommand=%d. Note=%d, Velocity=%d\n", midiCommand, note, velocity);
MIDINoteMessage noteMessage;
noteMessage.releaseVelocity = 0;
noteMessage.velocity = velocity;
noteMessage.note = note;
MusicTrackNewMIDINoteEvent(vc->musicTrack, packet->timeStamp, &noteMessage);
packet = MIDIPacketNext(packet);
}
}
I try to transform MIDIPklist on MIDINoteMessage to add it on my track.
When I have finished that, I create the file with this function :
-(void) createMidiFile
{
// init sequence
NewMusicSequence(&sequence);
CFURLRef pathUrl = (__bridge CFURLRef)[NSURL fileURLWithPath:self.path];
//set track to sequence
MusicSequenceNewTrack(sequence, &musicTrack);
// write sequence in file
MusicSequenceFileCreate(sequence,
pathUrl,
kMusicSequenceFile_MIDIType,
kMusicSequenceFileFlags_EraseFile,
0);
}
The file has been created but the data aren't correct. It have every time the same size.
Thanks if you can help me to debug that ! I don't understand what I have to do to fill the track and sequence object for create a good mid file...
Sorry for my english guys.. :)

Answer 1

I'm trying to solve same problem. From what I can see - the MIDINoteMessage needs to have a duration which corresponds to the delta of note on and subsequent note off call. You have to keep track of this.
The callback should be performed on main thread and you need to be using CACurrentMediaTime to stash the times midi timestamps prior to dumping out the midi file. Some of the code below.
The other alternative approach was sourced from apple forums
"Create a MusicSequence, add a MusicTrack to it, add some midi events to the track via MusicTrackNewMidiNoteEvent, set that MusicSequence on a newly created MusicPlayer, and start the player. Now that you have that player playing you can query it for the current time in beats via the MusicPlayerGetTime function. Set that time for the MusicTimeStamp for midi messages you send to MusicTrackNewMidiNoteEvent.
**Important Note - You MUST populate the MusicTrack for the MusicPlayer that you are querying for the time stamp, or it won't play! You'll get an error (probably (-50) depending on if you set everything else up correctly). I did this with a loop, adding a message with a time stamp starting at zero, going up to four. I would guess that you don't even have to go that high, but the Track has to have something for the player to play. Don't worry about it running off the end since all we want It for is the MusicTimeStamp. The MusicPlayer will continue playing until you tell it to stop."
This code is the closest I've come to answer - although this is targeting IOS.
https://github.com/benweitzman/ReTune/blob/ee47009999298c2b03527302c3fb6d7be17b10e2/Return4/ViewController.m
#interface NoteObject : NSObject
#property (nonatomic) int time;
#property (nonatomic) int note;
#property (nonatomic) int velocity;
#property (nonatomic) bool noteOn;
#end
- (void) midiSource:(PGMidiSource*)midi midiReceived:(const MIDIPacketList *)packetList
{
[self performSelectorOnMainThread:#selector(addString:)
withObject:#"MIDI received:"
waitUntilDone:NO];
const MIDIPacket *packet = &packetList->packet[0];
for (int i = 0; i < packetList->numPackets; ++i)
{
//[self performSelectorOnMainThread:#selector(addString:)
// withObject:[self StringFromPacket:packet]
// waitUntilDone:NO];
if (packet->length == 3) {
if ((packet->data[0]&0xF0) == 0x90) {
if (packet->data[2] != 0) {
[self noteOn:packet->data[1] withVelocity:packet->data[2]];
} else {
[self noteOff:packet->data[1]];
}
} else if ((packet->data[0]&0xF0) == 0x80) {
[self noteOff:packet->data[1]];
}
}
packet = MIDIPacketNext(packet);
}
}
- (void) noteOff:(int)noteValue {
//NSLog(#"off");
if (noteValue>=0 && noteValue<127) {
ALSource * source = [sources objectAtIndex:noteValue];
ALSource *loopSource = [loopSources objectAtIndex:noteValue];
if (source.playing || loopSource.playing) {
[[fadingOut objectAtIndex:noteValue] release];
[fadingOut replaceObjectAtIndex:noteValue withObject:[[NSNumber alloc] initWithBool:YES]];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
float timeDone = 0;
float duration = 0.2;
float timeStep = 0.01;
float valStep = source.gain*timeStep/duration;
float loopStep = loopSource.gain*timeStep/duration;
while (timeDone < duration) {
if (![[fadingOut objectAtIndex:noteValue] boolValue]) break;
source.gain -= valStep;
loopSource.gain -= loopStep;
[NSThread sleepForTimeInterval:timeStep];
timeDone += timeStep;
}
if ([[fadingOut objectAtIndex:noteValue] boolValue]) {
[source stop];
[loopSource stop];
}
//source.gain = 1;
});
if (recording) {
double currentTime = CACurrentMediaTime();
int deltaTime = (int)(currentTime*1000-recordTimer*1000);
NoteObject * recordedNote = [[NoteObject alloc] init];
recordedNote.note = noteValue;
recordedNote.time = deltaTime;
recordedNote.noteOn = false;
[recordedNotes addObject:recordedNote];
recordTimer = currentTime;
}
}
}
}
- (void) finishFadeIn:(ALSource*)source {
}
- (void) noteOn:(int)noteValue withVelocity:(int)velocity {
if (noteValue>=0 && noteValue<127) {
if (recording) {
double currentTime = CACurrentMediaTime();
int deltaTime = (int)(currentTime*1000-recordTimer*1000);
NoteObject * recordedNote = [[NoteObject alloc] init];
recordedNote.note = noteValue;
recordedNote.time = deltaTime;
recordedNote.noteOn = true;
[recordedNotes addObject:recordedNote];
recordTimer = currentTime;
}
while(loadingScale || changingPitch);
float pitchToPlay = [[ratios objectAtIndex:noteValue] floatValue];
[[fadingOut objectAtIndex:noteValue] release];
[fadingOut replaceObjectAtIndex:noteValue withObject:[[NSNumber alloc] initWithBool:NO]];
ALSource * source = [sources objectAtIndex:noteValue];
[source stop];
source.gain = velocity/127.0f;
source.pitch = pitchToPlay;
[source play:[buffers objectAtIndex:noteValue]];
if ([loopBuffers objectAtIndex:noteValue] != (id)[NSNull null]) {
ALSource *loopSource = [loopSources objectAtIndex:noteValue];
[loopSource stop];
loopSource.gain = 0;
loopSource.pitch = source.pitch;
[loopSource play:[loopBuffers objectAtIndex:noteValue] loop:YES];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
float timeDone = 0;
float duration = [(ALBuffer*)[buffers objectAtIndex:noteValue] duration]-.4;
float timeStep = 0.01;
float valStep = source.gain*timeStep/duration;
float loopStep = valStep;
while (timeDone < duration) {
if ([[fadingOut objectAtIndex:noteValue] boolValue]) break;
source.gain -= valStep;
loopSource.gain += loopStep;
[NSThread sleepForTimeInterval:timeStep];
timeDone += timeStep;
}
/*if ([[fadingOut objectAtIndex:noteValue] boolValue]) {
[source stop];
[loopSource stop];
}*/
//source.gain = 1;
});
}
/*
[source play];*/
//[[sources objectAtIndex:noteValue] play:toPlay gain:velocity/127.0f pitch:pitchToPlay pan:0.0f loop:FALSE];
}
}