Fix numpy.frombuffer() ValueError: buffer size must be a multiple of element size – NumPy Tutorial

By | October 26, 2022
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When we are using numpy.frombuffer() to convert a bytes to numpy array, we may get this error: ValueError: buffer size must be a multiple of element size. In this tutorial, we will introduce you how to fix this error.

Look at this example:

import librosa
wav_file = "music-jamendo-0039.wav"
wav_data, sr = librosa.load(wav_file, mono=True)
print(wav_data)
print(wav_data.dtype)
import numpy as np
print(wav_data[0:50])
b = wav_data.tobytes()

x = np.frombuffer(b, dtype = np.float)
print(type(x))
print(x[0:50])

Here we use np.float to convert a bytes to numpy array.

x = np.frombuffer(b, dtype = np.float)

Run this code, we will see: ValueError: buffer size must be a multiple of element size

Fix numpy.frombuffer() ValueError buffer size must be a multiple of element size - NumPy Tutorial

How to fix this error?

We should set dtype in numpy.frombuffer() correctly.

For example:

If dtype = np.int16

x = np.frombuffer(b, dtype = np.int16)

We will find x is:

[-24422  13481 -24658  13714  -8626 -18935 -17005  13767 -23484  13714
  12668 -18760  19671  14155 -22622  14337 -14007  14086  30525 -18655
  -1029  14063  31102  13097  -3852 -18456  12771 -18522  26295  13852
  -8508  13838 -27266 -18925  -4946  13532   3331  13702  -4075 -19116
 -25870 -19160  28735  13790   5765 -19113  24229 -18936  25993  13996]

The value of x is not the same to wav_data.

In order to get the right value of x, we should set dtype = np.float32, which is the dtype of wav_data.

Here x is:

[ 3.1595556e-07  1.0924321e-06 -2.0543989e-06  1.4881829e-06
  1.0925655e-06 -5.4893881e-06  1.2117634e-05  3.0912117e-05
  8.0338878e-06 -9.6241101e-06  7.1520894e-06  3.9458875e-08
 -2.7768758e-05 -1.9811972e-05  2.3305599e-06  2.1289316e-06
 -2.1991723e-06  4.1150400e-07  9.9875649e-07 -7.9325520e-07
 -6.2810352e-07  1.6572957e-06 -8.0126512e-07 -2.0320670e-06
  5.1378197e-06 -5.1078187e-06 -2.8517738e-05 -1.7178845e-05
  7.3522529e-06 -6.6071664e-07 -4.5573697e-06  8.0500204e-06
 -8.8221705e-06 -3.0072155e-05 -1.2288952e-05  5.9455974e-06
 -6.2966063e-07 -2.5200138e-06  2.6032403e-06 -4.4498762e-07
 -1.7536241e-06  1.9865117e-06 -3.9684135e-08 -2.2182173e-06
  2.2615259e-06  8.9228968e-07 -5.3025328e-06  6.0253165e-06
  2.5768280e-05  1.8642553e-05]

The value of x is same to wav_data.

Finally, this error is fixed.

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