audio.ex

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 == Opus 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_parser(input_format)
    |> maybe_plug_decoder(input_format)
    |> maybe_plug_resampler(input_format, output_format)
    |> maybe_plug_encoder(output_format)
  end

  defp maybe_plug_parser(builder, %AAC{}) do
    builder |> child(:aac_parser, AAC.Parser)
  end

  defp maybe_plug_parser(builder, _input_format) do
    builder
  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