Write multiple streams using pipes

I work with multistream audio files in ffmpeg:

ffmpeg -i stream1.m4a -i stream2.m4a -map 0:1 -map 0:2 out.m4a

As I understand this has been discussed here this is supported. Is this correct?

Now is there a way to use pipes as input and doing this in ffmpeg-python so that I can create multistream outputs from e.g. numpy arrays?

Here is an example what I use for single stream outputs:

# audio: numpy array
process = ffmpeg.input('pipe:', format='f32le').output(path).run_async()
process.stdin.write(audio.astype('<f4').tobytes())

[faroit]

As a workaround for muxing multiple stereo streams into one multistream file (e.g. two stereo audio file into a single 2-stream audio file), I came up with the idea of stacking the stereo streams into multiple channels and use a complex filter to map the channels to streams such as:

ffmpeg -y -i in.wav -filter_complex "\
  [a:0]pan=stereo| c0=c0 | c1=c1[a0]; \
  [a:0]pan=stereo| c0=c2 | c1=c3[a1]; \
  " -map "[a0]" -map "[a1]" -c:a pcm_s16le out.mka

Would this be implementable in ffmpeg-python? @loretoparisi @kkroening

[faroit]

@loretoparisi I managed to do this now with -complex_filter and multiple maps. Is there an example how to use -complex_filter in ffmpeg-python?