how to split midi files into windows of x bars about drywetmidi HOT 10 CLOSED

Hi,

I want to split a midi file into windows of 8 bars, with a step size of 1 bar

So what the length of each new MIDI file? 1 bar or 8 bars?

from drywetmidi.

Thanks for the quick reply!

8 bars. Then move 1 bar forward in time, and generate the next 8 bars from the file. And so on, until I reach the end of the file (the last 8 bar sequence)

Does that make sense?

from drywetmidi.

Thanks for clarification. Please try this code:

using Melanchall.DryWetMidi.Smf;
using Melanchall.DryWetMidi.Smf.Interaction;
using Melanchall.DryWetMidi.Tools;

// ...

var newFiles = midiFile.SplitByGrid(
    new SteppedGrid(new BarBeatTimeSpan(8, 0), new BarBeatTimeSpan(1, 0)));

This code splits midiFile into new files with length of 8 bars and 1 bar:

|--------|-|--------|-|--------|-|--------|-|--------|

Just remove files with length of 1 bar (every second) and you'll get desired result. If it's supposed that 1-bar files will be empty you can try to set RemoveEmptyFiles to true on SplittingMidiFileByGridSettings passed to SplitByGrid:

var newFiles = midiFile.SplitByGrid(
    new SteppedGrid(new BarBeatTimeSpan(8, 0), new BarBeatTimeSpan(1, 0)),
    new SplittingMidiFileByGridSettings
    {
        RemoveEmptyFiles = true
    });

You can find more information about MIDI file splitting on the library Wiki: MIDI file splitter. Please note that SplittingMidiFileByGridSettings has some useful properties that can help you to get desired result.

Thanks for your case. It seems it will be useful to add kind of Margin property to implementations of IGrid to support scenarios like yours.

from drywetmidi.

Wow, thanks so much for this!

But actually, it's not what I meant:

Let's take this line as being a musical piece, each - being a bar.

|--------|----------...

In the above I have extracted an 8-bar segment.

I then want to extract the next 8-bar segment, but with a step size of 1

-|--------|---------...

Does that make sense?

The code you provided extracts an 8-bar segments, then moves 9 bars as a step, and then extracts the next 8bar segment

from drywetmidi.

No, it extracts 8-bar file, then extracts 1-bar file, then extracts 8-bar file and so on :) You just need to ignore those files with length of 1 bar.

from drywetmidi.

Yes, I understand that. But that's now what I want.

Given a piece like this and an initial 8 bar segment.

|--------|----------...

I don't want to move 1 bar starting after the segment, but from the beginning

-|--------|---------...

As compared with what you are doing, where the next segment would be this:

---------|--------|-...

It's a sliding window.

from drywetmidi.

Oh, sorry, finally got it :) I'll try to provide you a solution a bit later.

from drywetmidi.

Thanks a lot !

I am trying myself to figure it out, but my C# skills aren't as sharp as they used to be...

from drywetmidi.

Please try this code:

var result = new List<MidiFile>();
var windowSize = 8;

for (var i = 0; ; i++)
{
    var startTime = new BarBeatTimeSpan(i, 0);
    var endTime = new BarBeatTimeSpan(i + windowSize, 0);

    var grid = new ArbitraryGrid(new[] { startTime, endTime });
    var newFiles = midiFile.SplitByGrid(grid).ToList();

    if (!newFiles.Any())
        break;
    else if (newFiles.Count == 1)
        result.Add(newFiles[0]);
    else
    {
        var secondNewFile = newFiles[1];
        var tempoMap = secondNewFile.GetTempoMap();
        var length = secondNewFile.GetTimedEvents().LastOrDefault()?.TimeAs<BarBeatTimeSpan>(tempoMap);

        if (length.Bars == windowSize || (length.Bars == windowSize - 1 && length.Beats > 0 && length.Ticks > 0))
            result.Add(secondNewFile);
        else
            break;
    }
}

length.Bars == windowSize || (length.Bars == windowSize - 1 && length.Beats > 0 && length.Ticks > 0) means

• length of new file is exactly of window size; or
• length of new file is windowSize - 1 but it close to window size, so 7.3.99 will be considered as 8 bars; this condition is placed for cases of rounding errors during time/length conversions.

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Thanks a lot, that worked!

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