Create a pipe of input and output for wav to mp3 encoding

I have to pipe a wave data stream to ffmpeg in Python. I can easily create an output pipe from an input mp3 file like:

           process = (
                ffmpeg
                .input(path)
                .output('pipe:', **output_kwargs)
                .run_async(pipe_stdout=True, pipe_stderr=True))
            buffer, _ = process.communicate()
            # because of we need (n_channels, samples)
            waveform = np.frombuffer(buffer, dtype='<f4').reshape(-1, n_channels)
            if not waveform.dtype == np.dtype(dtype):
                waveform = waveform.astype(dtype)

Here waveform will contain the wave audio file.

Now, I want to pipe the same data, but from an input stream, but for some reason it does not work as expected:

        # data shape is like (9161728, 2) for two channels audio data
        input_kwargs = {'ar': sample_rate, 'ac': data.shape[1]} 
        output_kwargs = {'ar': sample_rate, 'strict': '-2'}
        n_channels = 2
        process = (
            ffmpeg
            .input('pipe:', format='f32le', **input_kwargs)
            .output('pipe:', **output_kwargs)
            .run_async(pipe_stdin=True, quiet=True))
        buffer, err = process.communicate(input=data.astype('<f4').tobytes())

The output buffer is empty here after getting the results from process.communicate, while err is

Unable to find a suitable output format for 'pipe:'\npipe:: Invalid argument\n"

[RobertLucian]

@loretoparisi, @kkroening has this issue been addressed? When I pipe in and out, I also have this issue where if I write a couple of times to stdin then at some point the stdin.write() call just hangs indefinitely - it’s slightly different from @loretoparisi’s issue, but I think it’s the same issue at its core.

Mine looks like this:

process = (
        ffmpeg.input("pipe:", format="rawvideo", pix_fmt="rgb24", s=f"{width}x{height}")
        .output("pipe:", format="matroska", pix_fmt="yuv420p")
        .run_async(pipe_stdin=True, pipe_stdout=True)
)

Then doing process.stdin.write(<bytes object from image>) repeatedly will hang after some time - this is very consistent behavior, as it happens for every video that I pass in.

When a single pipe is used (either for the input or the output), it then starts working again. An example of this is the following:

process = (
        ffmpeg.input("pipe:", format="rawvideo", pix_fmt="rgb24", s=f"{width}x{height}")
        .output(file_path, pix_fmt="yuv420p")
        .run_async(pipe_stdin=True)
)

[Vulcanostrol]

Is there an update on this? I would imagine piping is something we would want to have working well?