Python Wave Library String to Bytes

Question

So basically I am trying to read in the information of a wave file so that I can take the byte information and create an array of time->amplitude points.

import wave

class WaveFile:

    # `filename` is the name of the wav file to open
    def __init__(self, fileName):
        self.wf = wave.open(fileName, 'r')
        self.soundBytes = self.wf.readframes(-1)
        self.timeAmplitudeArray = self.__calcTimeAmplitudeArray()


     def __calcTimeAmplitudeArray(self):
         self.internalTimeAmpList = [] # zero out the internal representation

         byteList = self.soundBytes
         if((byteList[i+1] & 0x080) == 0):
             amp = (byteList[i] & 0x0FF) + byteList[i+1] << 8
             #more code continues.....

Error:

if((int(byteList[i+1]) & 0x080) == 0):
TypeError: unsupported operand type(s) for &: 'str' and 'int'

I have tried using int() to convert to integer type, but to no avail. I come from a Java background where this would done using the byte type, but that does not appear to be a language feature of Python. Any direction would be appreciated.

score 2 · Answer 1 · edited May 23 '17 at 11:57

Your problem comes from the fact that the wave library is just giving you raw binary data (in the form of a string).

You'll probably need to check the form of the data with self.wf.getparams(). This returns (nchannels, sampwidth, framerate, nframes, comptype, compname). If you do have 1 channel, a sample width of 2, and no compression (fairly common type of wave), you can use the following (import numpy as np) to get the data:

byteList = np.fromstring(self.soundBytes,'<h')

This returns a numpy array with the data. You don't need to loop. You'll need something different in the second paramater if you have a different sample width. I've tested with with a simple .wav file and plot(byteList); show() (pylab mode in iPython) worked.

See Reading *.wav files in Python for other methods to do this.

Numpyless version

If you need to avoid numpy, you can do:

import array
bytelist = array.array('h')
byteList.fromstring(self.soundBytes)

This works like before (tested with plot(byteList); show()). 'h' means signed short. len, etc. works. This does import the wav file all at once, but then again .wav usually are small. Not always.

Unfortunately I cannot use numpy because our developers work on 64 bit windows machines. — thatidiotguy, May 20 '13 at 19:12
Anyway, use self.wf.getnframes() to get the length of the array. — Henry Schreiner, May 20 '13 at 19:19
By the way, I usually use 32 bit python on 64 bit windows, so I use the offical builds of numpy, etc. If you run 64 bit python, this very useful site should help: [Unofficial Windows Binaries for Python Extension Packages](http://www.lfd.uci.edu/~gohlke/pythonlibs/#numpy). If you are interested in going that route. — Henry Schreiner, May 20 '13 at 19:39

Fredrik Pihl · Accepted Answer · 2013-05-20T19:11:05.930

I usually use the array-module for this and the fromstring method.

My standard-pattern for operating on chunks of data is this:

def bytesfromfile(f):
    while True:
        raw = array.array('B')
        raw.fromstring(f.read(8192))
        if not raw:
            break
        yield raw

with open(f_in, 'rb') as fd_in:
    for byte in bytesfromfile(fd_in):
        # do stuff

Above 'B' denotes unsigned char, i.e. 1-byte.

If the file isn't huge, then you can just slurp it:

In [8]: f = open('foreman_cif_frame_0.yuv', 'rb')

In [9]: raw = array.array('B')

In [10]: raw.fromstring(f.read())

In [11]: raw[0:10]
Out[11]: array('B', [10, 40, 201, 255, 247, 254, 254, 254, 254, 254])

In [12]: len(raw)
Out[12]: 152064

Guido can't be wrong...

If you instead prefer numpy, I tend to use:

    fd_i = open(file.bin, 'rb')
    fd_o = open(out.bin, 'wb')

    while True:
        # Read as uint8
        chunk = np.fromfile(fd_i, dtype=np.uint8, count=8192)
        # use int for calculations since uint wraps
        chunk = chunk.astype(np.int)
        if not chunk.any():
            break
        # do some calculations
        data = ...

        # convert back to uint8 prior to writing.
        data = data.astype(np.uint8)
        data.tofile(fd_o)

    fd_i.close()
    fd_o.close()

or to read the whole-file:

In [18]: import numpy as np

In [19]: f = open('foreman_cif_frame_0.yuv', 'rb')

In [20]: data = np.fromfile(f, dtype=np.uint8)

In [21]: data[0:10]
Out[21]: array([ 10,  40, 201, 255, 247, 254, 254, 254, 254, 254], dtype=uint8)

Unfortunately I cannot use `numpy` as I am developing on 64 bit Windows. The end environment will be a linux box, but I develop on a Windows box. :( Could you explain the 8192 magic number in there? — thatidiotguy, May 20 '13 at 19:01
Then go for the array-approach. Added an example above... 8192 is just the chunk-size, in this case I'm reading 8192-bytes per iteration... — Fredrik Pihl, May 20 '13 at 19:03
What would be a good way to get the number of bytes from the return array? `len()` does not work on a "generator". Sorry, I am very new to Python so I don't know a lot about the standard libraries or even basic language syntax. — thatidiotguy, May 20 '13 at 19:11

Python Wave Library String to Bytes

2 Answers2

Numpyless version