How To Reverse Audio With Pyaudio

I've been tinkering around with pyaudio for a while now, trying to reverse a simple wave file with no success. In (my) theory I would only have to iterate from end to beginning thr

Solution 1:

If the file you want reversed is small enough to fit in memory, your best bet would be loading it entirely and reversing the data, then streaming it:

import pyaudio
import wave

wavefile_name = 'wavefile.wav'
wf = wave.open(wavefile_name, 'rb')

p = pyaudio.PyAudio()
stream = p.open(format =
                p.get_format_from_width(wf.getsampwidth()),
                channels = wf.getnchannels(),
                rate = wf.getframerate(),
                output = True)

full_data = []
data = wf.readframes(1024)

whiledata:    
    full_data.append(data)
    data = wf.readframes(1024)

data = ''.join(full_data)[::-1]

for i in range(0, len(data), 1024):
    stream.write(data[i:i+1024])

However, if the file is too big to fit in memory, you'll need some way of reading the file backwards and feed into the sound system. That's an entirely different problem, because it involves some low level I/O programming to handle the backward reading.

---

Edit: after seeing your full code, I don't see any errors. The code runs properly in my computer, only to fail at the ending of the playback. However, you can do two things. First, you can go to the end of the wavefile to play the entire sound backwards, using this:

wf = wave.open(sys.argv[1], 'rb')
index = wf.getnframes() - 1024
wf.setpos(index)

Second, you have to modify the callback so it doesn't fail when the seek head goes beyond the beginning of the file:

def callback(in_data, frame_count, time_info, status):
    global index
    data = wf.readframes(frame_count)
    data = data[::-1]
    index-=1024if index < 0:
        return (data, pyaudio.paAbort)
    else:
        wf.setpos(max(index,0))
        return (data, pyaudio.paContinue)

Other than that, it works pretty ok.