in whisper/timing.py [0:0]
def backtrace(trace: np.ndarray):
i = trace.shape[0] - 1
j = trace.shape[1] - 1
trace[0, :] = 2
trace[:, 0] = 1
result = []
while i > 0 or j > 0:
result.append((i - 1, j - 1))
if trace[i, j] == 0:
i -= 1
j -= 1
elif trace[i, j] == 1:
i -= 1
elif trace[i, j] == 2:
j -= 1
else:
raise ValueError("Unexpected trace[i, j]")
result = np.array(result)
return result[::-1, :].T