Pipeline for muxing 2 msr files (audio and video) into a single flv file

spec = [
      # Part of pipeline which saves to FLV file
      # child(:muxer, Membrane.MP4.Muxer.ISOM)
      child(:muxer, Membrane.FLV.Muxer)
      |> child(:sink, %Membrane.File.Sink{location: output_file}),

      # Part of pipeline which reads from file and prepare video for muxing
      child(:source, %Membrane.File.Source{location: video_track_file})
      |> child(:deserializer_video, Membrane.Stream.Deserializer)
      |> child(:rtp_video, %Membrane.RTP.DepayloaderBin{
        depayloader: Membrane.RTP.H264.Depayloader,
        clock_rate: 90_000
      })
      |> child(:parser_video, %Membrane.H264.Parser{
        generate_best_effort_timestamps: %{framerate: {0, 1}},
        output_stream_structure: :avc1
      })
      |> via_in(Pad.ref(:video, 0))
      |> get_child(:muxer),
      # Part of pipeline which reads from file and prepare audio for muxing
      child(:source_audio, %Membrane.File.Source{location: audio_track_file})
      |> child(:deserializer_audio, Membrane.Stream.Deserializer)
      |> child(:rtp_audio, %Membrane.RTP.DepayloaderBin{
        depayloader: Membrane.RTP.Opus.Depayloader,
        clock_rate: 48_000
      })
      |> child(:opus_decoder, Membrane.Opus.Decoder)
      |> child(:aac_encoder, Membrane.AAC.FDK.Encoder)
      |> child(:aac_parser, %Membrane.AAC.Parser{
        out_encapsulation: :none,
        output_config: :audio_specific_config
      })
      |> via_in(Pad.ref(:audio, 0))
      |> get_child(:muxer)
    ]