Software Mansion•4mo ago

How do I invoke Pipeline.handle_info from a Phoenix.WebChannel?

I'm trying to pass audio from a Phoenix Web Channel to a Pipeline. Also, are there any notify_child usage examples? I don't understand how to use Membrane.Pipeline.notify_child. Do I need to define it first? If so, what should the definition look like? Update: I was able to pass a message to the pipeline by making the following changes to my Channel handle_inlike so:

def handle_in("new_audio", %{"data" => audio_data}, socket) do
    IO.inspect("pipelines: ")
    # IO.inspect(Membrane.Pipeline.list_pipelines())
    [head | _] = Membrane.Pipeline.list_pipelines()
    # IO.inspect(head)
    send(head, audio_data)
    {:noreply, socket}
  end

def handle_in("new_audio", %{"data" => audio_data}, socket) do
    IO.inspect("pipelines: ")
    # IO.inspect(Membrane.Pipeline.list_pipelines())
    [head | _] = Membrane.Pipeline.list_pipelines()
    # IO.inspect(head)
    send(head, audio_data)
    {:noreply, socket}
  end

But I got the error:

[error] <0.768.0>/ Error occured in Membrane Pipeline:
%Membrane.CallbackError{
  message: "Invalid value returned from AudioTranscription.StreamToFile.:handle_info:

[error] <0.768.0>/ Error occured in Membrane Pipeline:
%Membrane.CallbackError{
  message: "Invalid value returned from AudioTranscription.StreamToFile.:handle_info:

This is what my Membrane.Pipeline.handle_info looks like

@impl true
  def handle_info(audio_data, ctx, _state) do
    # Process the audio data
    IO.inspect("ctx")
    IO.inspect(ctx)
    IO.inspect("audio_data")
    IO.inspect(audio_data)
    # ctx.notify_child(AudioTranscription.Source, audio_data)
    # AudioTranscription.AudioSource.receive_audio_data(audio_data)
  end

@impl true
  def handle_info(audio_data, ctx, _state) do
    # Process the audio data
    IO.inspect("ctx")
    IO.inspect(ctx)
    IO.inspect("audio_data")
    IO.inspect(audio_data)
    # ctx.notify_child(AudioTranscription.Source, audio_data)
    # AudioTranscription.AudioSource.receive_audio_data(audio_data)
  end

7 Replies

Noarkhh•4mo ago

Hi @Villain In Glasses All Membrane.Pipeline and Membrane.Element callbacks need to return a tuple of Actions and the next state (as shown here) notify_child is an action, so to use it you need to return it from the handle_info callback. In your case the return value in handle_info should probably look like this:

{[notify_child: {<child_name>, <your_message>}], state}

{[notify_child: {<child_name>, <your_message>}], state}

Thanks to this the specified child will receive the message after the handle_info callback execution finishes

Villain In Glasses•4mo ago

Oh, so that's how you use it. Thanks for the clarification. Also, now I'm getting another error:

 Error occured in Membrane Pipeline:
%Membrane.UnknownChildError{
  message: "Child of name AudioTranscription.Source doesn't exist. Available children are [].\n"
}

 Error occured in Membrane Pipeline:
%Membrane.UnknownChildError{
  message: "Child of name AudioTranscription.Source doesn't exist. Available children are [].\n"
}

Is this the wrong way to define specify children?

  @impl true
  def handle_init(_) do
    spec =
      child(AudioTranscription.Source)
      |> child(%Membrane.File.Sink{location: "output.wav"})

      {[spec: spec], %{}}
  end

  @impl true
  def handle_init(_) do
    spec =
      child(AudioTranscription.Source)
      |> child(%Membrane.File.Sink{location: "output.wav"})

      {[spec: spec], %{}}
  end

Noarkhh•4mo ago

to give your child a name that can be used to locate this child you need to explicitly specify it in the child function, otherwise the child will be anonymous. You could specify the name like this:

child(:source, AudioTranscription.Source)

child(:source, AudioTranscription.Source)

and the child would be available under name :source

Villain In Glasses•4mo ago

Nope, I updated the code to:

  @impl true
  def handle_init(_) do
    spec =
      child(:source, AudioTranscription.Source)
      |> child(:sink, %Membrane.File.Sink{location: "output.wav"})

      {[spec: spec], %{}}
  end

  @impl true
  def handle_info(audio_data, ctx, state) do
    # Process the audio data
    {[notify_child: {:source, audio_data}], state}
  end

  @impl true
  def handle_init(_) do
    spec =
      child(:source, AudioTranscription.Source)
      |> child(:sink, %Membrane.File.Sink{location: "output.wav"})

      {[spec: spec], %{}}
  end

  @impl true
  def handle_info(audio_data, ctx, state) do
    # Process the audio data
    {[notify_child: {:source, audio_data}], state}
  end

I'm still getting:

[error] <0.768.0>/ Error occured in Membrane Pipeline:
%Membrane.UnknownChildError{
  message: "Child of name :source doesn't exist. Available children are [].\n"

[error] <0.768.0>/ Error occured in Membrane Pipeline:
%Membrane.UnknownChildError{
  message: "Child of name :source doesn't exist. Available children are [].\n"

Noarkhh•4mo ago

handle_init has arity of 2, try

def handle_init(_ctx, _opts) do
...

def handle_init(_ctx, _opts) do
...

Villain In Glasses•4mo ago

Thank you so much! That worked 😄

Noarkhh•4mo ago

no problem, happy to help ;)

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How do I invoke Pipeline.handle_info from a Phoenix.WebChannel?