ffmpeg wav quad в mp3

Сначала quad в 4 моно файлах:ffmpeg -i den4.wav -filter_complex "[0:a]channelsplit=channel_layout=quad:channels=FL[left]" -map "[left]" front_left.mp3

и то же для остальных каналов (FR BL BR)

затем

ffmpeg -i front_left.mp3 -i front_right.mp3 -i back_left.mp3 -i back_right.mp3 -filter_complex "[0:a][1:a][2:a][3:a]join=inputs=4:channel_layout=quad[a]" -map "[a]" den4.mp3

Результат:

        Stream #0:0 (mp3float) -> join:input0
  Stream #1:0 (mp3float) -> join:input1
  Stream #2:0 (mp3float) -> join:input2
  Stream #3:0 (mp3float) -> join:input3
  join -> Stream #0:0 (libmp3lame)
Press [q] to stop, [?] for help
Output #0, mp3, to 'den4.mp3':
  Metadata:
    TSSE            : Lavf58.29.100
    Stream #0:0: Audio: mp3 (libmp3lame), 48000 Hz, stereo, fltp (default)

My original wav is sr 96000 and quad. How to keep channels and the sr as the input?

Thanks