从midi文件IOS读取时间签名(如4/4)

Question

花了将近半天的时间，我仍然无法理解如何使用iOS (目标c，CoreMIDI)从midi文件中获得4和4 (4/4)的值​​。

我有一个midi文件4/4 19巴120 bmp

我尝试了以下代码：

MusicTimeStamp inBeats;
UInt32 inSubbeatDivisor;
CABarBeatTime outBarBeatTime;
MusicSequenceBeatsToBarBeatTime(aSequence, inBeats, inSubbeatDivisor, &outBarBeatTime);

NSLog(@"%i, %i, %i, %i, %i, %f", outBarBeatTime.bar, outBarBeatTime.beat, outBarBeatTime.reserved, outBarBeatTime.subbeat, outBarBeatTime.subbeatDivisor, inBeats);

结果: 5，3,755，0,50617，0.000000

不知道如何处理这些来自NSLog的信息。

如果midi文件是6/2、4/2或5/8，那么我只想得到这个值(第二个/第一个)

有人能帮我算一下吗？谢谢!

Answer 1

MusicSequenceBeatsToBarBeatTime只是在两种不同格式之间转换时间戳，但它没有告诉您它用于转换的时间签名。

时间签名是使用节奏轨道中的时间签名元事件指定的。因此，您必须使用MusicSequenceGetTempoTrack获得节奏跟踪，使用MusicEventIterator搜索具有kMusicEventType_Meta类型的事件，并检查这些事件是否为时间签名元事件(如果时间签名更改，可能会出现多个时间签名事件)。

Answer 2

谢谢你的CL。用户经过小规模的实验后，我做了并得到了以下结果：

在这里，我们加载midi文件：

+(void) openMidiFile: (NSString *) path{

    MusicSequence s;
    NewMusicSequence(&s);


    NSURL * midiFileURL = [NSURL fileURLWithPath:path];

    MusicSequenceFileLoad(s, (CFURLRef)midiFileURL, 0, 0);

    //Get tempo and time signature
    [self getSequenceTempo:s];
}

在这里，我们从节奏轨道上获得所需的信息。

+(MusicTrack) getSequenceTempo: (MusicSequence) aSequence{
    OSStatus result = noErr;

    MusicTrack tempoTrack;

    result = MusicSequenceGetTempoTrack(aSequence, &tempoTrack);
    if (noErr != result) {
        NSLog(@"MusicSequenceGetTempoTrack, %d", (int)result);
    }

    // Create an interator
    MusicEventIterator iterator = NULL;
    NewMusicEventIterator(tempoTrack, &iterator);
    MusicTimeStamp timestamp = 0;
    MusicEventType eventType = 0;

    const void *eventData = NULL;
    UInt32 eventDataSize = 0;

    Boolean hasNext = YES;

    // A variable to store note messages
    ExtendedTempoEvent * message;
    MIDIMetaEvent *metaEvent;

    // Iterate over events
    while (hasNext) {

        // See if there are any more events
        MusicEventIteratorHasNextEvent(iterator, &hasNext);

        // Copy the event data into the variables we prepaired earlier
        MusicEventIteratorGetEventInfo(iterator, &timestamp, &eventType, &eventData, &eventDataSize);

        // Process Midi Note messages
        if(eventType==kMusicEventType_ExtendedTempo) {
            // Cast the midi event data as a midi note message
            message = (ExtendedTempoEvent*) eventData;
            // NSLog(@"%f", message->bpm); //TEMPO VALUE

        }
        if (eventType == kMusicEventType_Meta){
            metaEvent = (MIDIMetaEvent *) eventData;

            for (int i = 0; i < metaEvent->dataLength;i++){
                NSLog(@"%i, %i, %i, %i, %i", metaEvent->metaEventType, metaEvent->data[i], metaEvent->unused1, metaEvent->unused2, metaEvent->unused3);
            }
            NSLog(@"...");
        }

        MusicEventIteratorNextEvent(iterator);
    }


    return tempoTrack;
}

结果是：

**For 7/8:**
2014-09-17 14:03:14.073 MidiSequencer[1959:907] 88, **7**, 224, 215, 47
2014-09-17 14:03:14.075 MidiSequencer[1959:907] 88, **3**, 224, 215, 47
2014-09-17 14:03:14.077 MidiSequencer[1959:907] 88, 36, 224, 215, 47
2014-09-17 14:03:14.079 MidiSequencer[1959:907] 88, 8, 224, 215, 47
2014-09-17 14:03:14.080 MidiSequencer[1959:907] ...
2014-09-17 14:03:14.081 MidiSequencer[1959:907] 88, **7**, 224, 215, 47
2014-09-17 14:03:14.083 MidiSequencer[1959:907] 88, **3**, 224, 215, 47
2014-09-17 14:03:14.084 MidiSequencer[1959:907] 88, 36, 224, 215, 47
2014-09-17 14:03:14.086 MidiSequencer[1959:907] 88, 8, 224, 215, 47 


**For 7/4**
2014-09-17 13:59:45.455 MidiSequencer[1922:907] 88, **7**, 32, 220, 47
2014-09-17 13:59:45.457 MidiSequencer[1922:907] 88, **2**, 32, 220, 47
2014-09-17 13:59:45.459 MidiSequencer[1922:907] 88, 36, 32, 220, 47
2014-09-17 13:59:45.461 MidiSequencer[1922:907] 88, 8, 32, 220, 47
2014-09-17 13:59:45.462 MidiSequencer[1922:907] 88, **7**, 32, 220, 47
2014-09-17 13:59:45.464 MidiSequencer[1922:907] 88, **2**, 32, 220, 47
2014-09-17 13:59:45.465 MidiSequencer[1922:907] 88, 36, 32, 220, 47
2014-09-17 13:59:45.466 MidiSequencer[1922:907] 88, 8, 32, 220, 47

因此，如果我们看7/4的例子，这里有值:7和值:2。第二个值是:0是1；1是2；2是4；3是8，4是16;