Initial implementation

README.md

@@ -1,31 +1,27 @@
-# Membrane Template Plugin
+# Membrane Transcider Plugin
 
 [![Hex.pm](https://img.shields.io/hexpm/v/membrane_template_plugin.svg)](https://hex.pm/packages/membrane_template_plugin)
 [![API Docs](https://img.shields.io/badge/api-docs-yellow.svg?style=flat)](https://hexdocs.pm/membrane_template_plugin)
 [![CircleCI](https://circleci.com/gh/membraneframework/membrane_template_plugin.svg?style=svg)](https://circleci.com/gh/membraneframework/membrane_template_plugin)
 
-This repository contains a template for new plugins.
-
-Check out different branches for other flavors of this template.
+This repository provides `Membrane.Transcoder` which is a bin that is capable 
+of transcoding the input audio or video stream into the descired one specified 
+with simple declarative API.
 
 It's a part of the [Membrane Framework](https://membrane.stream).
 
 ## Installation
 
-The package can be installed by adding `membrane_template_plugin` to your list of dependencies in `mix.exs`:
+The package can be installed by adding `membrane_transcoder_plugin` to your list of dependencies in `mix.exs`:
 
 ```elixir
 def deps do
   [
-    {:membrane_template_plugin, "~> 0.1.0"}
+    {:membrane_transcoder_plugin, "~> 0.1.0"}
   ]
 end
 ```
 
-## Usage
-
-TODO
-
 ## Copyright and License
 
 Copyright 2020, [Software Mansion](https://swmansion.com/?utm_source=git&utm_medium=readme&utm_campaign=membrane_template_plugin)

lib/transcoder.ex

@@ -0,0 +1,99 @@
+defmodule Membrane.Transcoder do
+  @moduledoc false
+  use Membrane.Bin
+
+  require __MODULE__.Audio
+  require __MODULE__.Video
+
+  alias __MODULE__.{Audio, ForwardingFilter, Video}
+  alias Membrane.{AAC, Funnel, H264, H265, Opus, RawAudio, RawVideo, RemoteStream, VP8}
+
+  @type stream_format ::
+          H264.t()
+          | H265.t()
+          | VP8.t()
+          | RawVideo.t()
+          | AAC.t()
+          | Opus.t()
+          | RemoteStream.t()
+          | RawAudio.t()
+
+  @type stream_format_module :: H264 | H265 | VP8 | RawVideo | AAC | Opus | RawAudio
+
+  @type stream_format_resolver :: (stream_format() -> stream_format() | stream_format_module())
+
+  def_input_pad :input,
+    accepted_format: format when Audio.is_audio_format(format) or Video.is_video_format(format)
+
+  def_output_pad :output,
+    accepted_format: format when Audio.is_audio_format(format) or Video.is_video_format(format)
+
+  def_options output_stream_format: [
+                spec: stream_format() | stream_format_module() | stream_format_resolver()
+              ]
+
+  @impl true
+  def handle_init(_ctx, opts) do
+    spec = [
+      bin_input()
+      |> child(:forwarding_filter, ForwardingFilter),
+      child(:output_funnel, Funnel)
+      |> bin_output()
+    ]
+
+    state =
+      opts
+      |> Map.from_struct()
+      |> Map.put(:input_stream_format, nil)
+
+    {[spec: spec], state}
+  end
+
+  @impl true
+  def handle_child_notification(
+        {:stream_format, format},
+        :forwarding_filter,
+        _ctx,
+        %{input_stream_format: nil} = state
+      ) do
+    state =
+      %{state | input_stream_format: format}
+      |> resolve_output_stream_format()
+
+    spec =
+      get_child(:forwarding_filter)
+      |> plug_transcoding(format, state.output_stream_format)
+      |> get_child(:output_funnel)
+
+    {[spec: spec], state}
+  end
+
+  @impl true
+  def handle_child_notification(_notification, _element, _ctx, state) do
+    {[], state}
+  end
+
+  defp resolve_output_stream_format(state) do
+    case state.output_stream_format do
+      format when is_struct(format) ->
+        state
+
+      module when is_atom(module) ->
+        %{state | output_stream_format: struct(module)}
+
+      resolver when is_function(resolver) ->
+        %{state | output_stream_format: resolver.(state.input_stream_format)}
+        |> resolve_output_stream_format()
+    end
+  end
+
+  defp plug_transcoding(builder, input_format, output_format)
+       when Audio.is_audio_format(input_format) do
+    builder |> Audio.plug_audio_transcoding(input_format, output_format)
+  end
+
+  defp plug_transcoding(builder, input_format, output_format)
+       when Video.is_video_format(input_format) do
+    builder |> Video.plug_video_transcoding(input_format, output_format)
+  end
+end

lib/transcoder/audio.ex

@@ -0,0 +1,116 @@
+defmodule Membrane.Transcoder.Audio do
+  @moduledoc false
+
+  import Membrane.ChildrenSpec
+  require Membrane.Logger
+  alias Membrane.{AAC, ChildrenSpec, Opus, RawAudio, RemoteStream}
+
+  @opus_sample_rate 48_000
+  @aac_sample_rates [
+    96_000,
+    88_200,
+    64_000,
+    48_000,
+    44_100,
+    32_000,
+    24_000,
+    22_050,
+    16_000,
+    12_000,
+    11_025,
+    8000
+  ]
+
+  @type audio_stream_format :: AAC.t() | Opus.t() | RawAudio.t()
+
+  defguard is_audio_format(format)
+           when is_struct(format) and
+                  (format.__struct__ in [AAC, Opus, RawAudio] or
+                     (format.__struct__ == RemoteStream and format.content_format in [Opus, AAC] and
+                        format.type == :packetized))
+
+  @spec plug_audio_transcoding(
+          ChildrenSpec.builder(),
+          audio_stream_format() | RemoteStream.t(),
+          audio_stream_format()
+        ) :: ChildrenSpec.builder()
+  def plug_audio_transcoding(builder, input_format, output_format)
+      when is_audio_format(input_format) and is_audio_format(output_format) do
+    do_plug_audio_transcoding(builder, input_format, output_format)
+  end
+
+  defp do_plug_audio_transcoding(builder, %format_module{}, %format_module{}) do
+    Membrane.Logger.debug("""
+    This bin will only forward buffers, as the input stream format is the same as the output stream format.
+    """)
+
+    builder
+  end
+
+  defp do_plug_audio_transcoding(builder, %RemoteStream{content_format: Opus}, %Opus{}) do
+    builder |> child(:opus_parser, Opus.Parser)
+  end
+
+  defp do_plug_audio_transcoding(builder, input_format, output_format) do
+    builder
+    |> maybe_plug_decoder(input_format)
+    |> maybe_plug_resampler(input_format, output_format)
+    |> maybe_plug_encoder(output_format)
+  end
+
+  defp maybe_plug_decoder(builder, %Opus{}) do
+    builder |> child(:opus_decoder, Opus.Decoder)
+  end
+
+  defp maybe_plug_decoder(builder, %RemoteStream{content_format: Opus, type: :packetized}) do
+    builder |> child(:opus_decoder, Opus.Decoder)
+  end
+
+  defp maybe_plug_decoder(builder, %AAC{}) do
+    builder |> child(:aac_decoder, AAC.FDK.Decoder)
+  end
+
+  defp maybe_plug_decoder(builder, %RawAudio{}) do
+    builder
+  end
+
+  defp maybe_plug_resampler(builder, %{sample_rate: sample_rate} = input_format, %Opus{})
+       when sample_rate != @opus_sample_rate do
+    builder
+    |> child(:resampler, %Membrane.FFmpeg.SWResample.Converter{
+      output_stream_format: %RawAudio{
+        sample_format: :s16le,
+        sample_rate: @opus_sample_rate,
+        channels: input_format.channels
+      }
+    })
+  end
+
+  defp maybe_plug_resampler(builder, %{sample_rate: sample_rate} = input_format, %AAC{})
+       when sample_rate not in @aac_sample_rates do
+    builder
+    |> child(:resampler, %Membrane.FFmpeg.SWResample.Converter{
+      output_stream_format: %RawAudio{
+        sample_format: :s16le,
+        sample_rate: 44_100,
+        channels: input_format.channels
+      }
+    })
+  end
+
+  defp maybe_plug_resampler(builder, _input_format, _output_format) do
+    builder
+  end
+
+  defp maybe_plug_encoder(builder, %Opus{}) do
+    builder |> child(:opus_encoder, Opus.Encoder)
+  end
+
+  defp maybe_plug_encoder(builder, %AAC{}) do
+    builder |> child(:aac_encoder, AAC.FDK.Encoder)
+  end
+
+  defp maybe_plug_encoder(builder, %RawAudio{}) do
+    builder
+  end
+end