transcode flac into alac in mkv files

flac2alac.py

import os
import subprocess as sp

recursive = True
src_dir = '.'
src_dir = os.path.abspath(src_dir)

def encode(tar_fp, dst_dir_fp):
    dst_fp = os.path.join(dst_dir_fp, os.path.basename(tar_fp).replace('FLAC', 'ALAC'))
    p = sp.Popen(['mkvmerge', '-i', tar_fp], stdout=sp.PIPE, stderr=sp.PIPE)
    mkvinfo = p.communicate()[0].decode()
    aids, exceptstr = [], '!'
    for line in mkvinfo.splitlines():
        if '(FLAC)' in line:
            aids.append(int(line.split(':')[0].split('ID')[-1]))
            exceptstr += f'{aids[-1]},'
    extract_cmd = ['mkvextract', tar_fp, 'tracks']
    for aid in aids:
        extract_cmd.append(f'{aid}:_tmp_{aid}.flac')
    _ = sp.run(extract_cmd)
    for aid in aids:
        _ = sp.run(['qaac64', '-o', f'_tmp_{aid}.alac', '-A', f'_tmp_{aid}.flac'])
    merge_cmd = ['mkvmerge', '-o', dst_fp, '-a', exceptstr[:-1], tar_fp]
    merge_cmd += [f'_tmp_{aid}.alac' for aid in aids]
    _ = sp.run(merge_cmd)
    for aid in aids:
        os.remove(f'_tmp_{aid}.alac')
        os.remove(f'_tmp_{aid}.flac')
    
if __name__ == '__main__':
    if recursive:
        for root, dirs, files in os.walk(src_dir):
            os.chdir(root)
            dst_dir = os.path.join(root, 'flac2alac')
            os.makedirs(dst_dir, exist_ok=True)
            for fn in files:
                if not fn.endswith('.mkv'):
                    continue
                tar = os.path.join(root, fn)
                encode(tar, dst_dir)
    else:
        os.chdir(src_dir)
        dst_dir = os.path.join(src_dir, 'flac2alac')
        os.makedirs(dst_dir, exist_ok=True)
        for fn in os.listdir(src_dir):
            tar = os.path.join(src_dir, fn)
            if not fn.endswith('.mkv'):
                continue
            if not os.path.isfile(tar):
                continue
            encode(tar, dst_dir)