Converting a BRSTM to LWAV

import os
import struct
import subprocess

def convert_to_lwav(filename,loop_start,loop_end):
    _file = open(filename,'rb')
    content = _file.read()
    _file.close()
    #Append smpl chunk
    smpl_chunk_size = 60
    bytes_after_chunk_size = '\x00' * 28 + struct.pack('<i', 1) + '\x00' * 12
    ending_bytes = '\x00' * 8

    content += 'smpl' + struct.pack('<i', smpl_chunk_size) + bytes_after_chunk_size
    content += struct.pack('<i',loop_start) + struct.pack('<i',loop_end)
    content += ending_bytes
    #Update the RIFF header chunk size
    riff_index = content.index('RIFF')
    riff_header_chunk_size = struct.unpack('<i', content[riff_index + len('RIFF'):riff_index + len('RIFF') + 4])
    riff_header_chunk_size = int(riff_header_chunk_size[0])
    riff_header_chunk_size += len('smpl') + smpl_chunk_size
    new_content = content[0:riff_index + len('RIFF')] + struct.pack('<i', riff_header_chunk_size)
    new_content += content[len(new_content):]
    _file = open(filename,'wb')
    _file.write(new_content)
    _file.close()

def get_info(file_info, required_info):
    info = file_info[file_info.index(required_info):]
    info = info[:info.index('\n')]
    info = int(info.strip().split('=')[1])
    return info

def main():
    for dirpath, dirnames, filenames in os.walk('.'):
        pass
    #filenames = [filename for filename in filenames if os.path.splitext(filename)[1] == '.brstm']
    filenames = ['STRM_N_FACTORY_N.brstm']
    for filename in filenames:
        file_info = subprocess.check_output(['test','-b',filename])
        number_of_channels = get_info(file_info, 'chan')
        loop_start = get_info(file_info, 'lstart')
        loop_end = get_info(file_info, 'lend')
        for i in range(0,number_of_channels/2):
            out_filename = os.path.splitext(filename)[0] + '_{0}.lwav'.format(i)
            subprocess.call(['test',
                '-o',out_filename,
                '-l','1',
                '-f','0',
                '-d','0',
                '-2',str(i),
                filename])
            convert_to_lwav(out_filename,loop_start,loop_end)

if __name__ == '__main__':
    main()