Python

import wave

wr = wave.open("in.wav", mode="rb")
ww = wave.open("out.wav", mode="wb")
nchannels, sampwidth, framerate, nframes, comptype, compname = wr.getparams()
ww.setparams((2, sampwidth, framerate, nframes, comptype, compname))
frames = wr.readframes(wr.getnframes() - 1)
frames_len = len(frames)
frames_half_len = int(frames_len / 2)
offset = 0
frames1 = frames[0:frames_half_len - offset]
frames2 = frames[frames_half_len - offset:frames_len]
frames_len = len(frames1)
frames_half_len = int(frames_len / 2)
frame1 = frames1[0:frames_half_len - offset]
frame2 = frames1[frames_half_len - offset:frames_len]
frames_len = len(frames2)
frames_half_len = int(frames_len / 2)
frame3 = frames2[0:frames_half_len - offset]
frame4 = frames2[frames_half_len - offset:frames_len]
ww.writeframes(frame3)
ww.writeframes(frame4)
ww.writeframes(frame1)
ww.writeframes(frame2)
wr.close()
ww.close()