Propagate time-range annotations (chords) down to a list of reference times (beats)

beats_to_chords.py

def beats_to_chords(beat_times, chord_times, chord_labels):
    '''Propagate lab-style annotations to a list of beat timings.
              
    :parameters:
      - beat_times : ndarray, shape=(m, 2)
          The time range for beat intervals.
          The `i`th beat spans time `beat_times[i, 0]` to `beat_times[i, 1]`.
          `beat_times[0, 0]` should be 0, `beat_times[-1, 1]` should be the track duration.
          
      - chord_times : ndarray, shape=(n, 2)
          The time range for the `i`th annotation is `chord_times[i,0]` to `chord_times[i, 1]`.
          `chord_times[0, 0]` should be 0, `chord_times[-1, 1]` should be the track duration.
          
      - chord_labels : list of str, shape=(n,)
          List of annotation strings associated with `chord_times`
          
    :returns:
      - beat_labels : list of str, shape=(len(beat_times)-1,)
          Chord annotations at the beat level.
    '''
    
    # The overlap score of a beat with a segment is defined as
    #   max(0, min(beat_end, segment_end) - max(beat_start, segment_start))
    
    ends   = np.minimum.outer(beat_times[:, 1], chord_times[:, 1])
    starts = np.maximum.outer(beat_times[:, 0], chord_times[:, 0])
    
    score  = np.maximum(0, ends - starts)
    
    return [chord_labels[c] for c in np.argmax(score, axis=1)]