Hello friends, I'm trying to get microphone input (via Membrane.PortAudio.Source) packaged into an RTP stream and sent to a server and can't quite seem to get it right.

Excerpt below based on the demo in membrane-demo/rtp but with microphone input substituted and newer syntax.

alias Membrane.{RTP, UDP, PortAudio, RawAudio}
...
links = [
      child(:mic_input, %PortAudio.Source{
        channels: 2,
        sample_rate: 24_000
      })
      |> child(:encoder, %Membrane.Opus.Encoder{
        application: :audio,
        input_stream_format: %RawAudio{
          channels: 2,
          sample_format: :s16le,
          sample_rate: 24_000
        }
      })
      |> via_in(Pad.ref(:input, audio_ssrc), options: [payloader: RTP.Opus.Payloader])
      |> child(:rtp, %RTP.SessionBin{
        secure?: secure?,
        srtp_policies: [
          %ExLibSRTP.Policy{
            ssrc: :any_inbound,
            key: srtp_key
          }
        ]
      })
      |> via_out(Pad.ref(:rtp_output, audio_ssrc), options: [encoding: :OPUS])
      |> child(:audio_realtimer, Membrane.Realtimer)
      |> child(:audio_sink, %UDP.Sink{
        destination_port_no: destination_port,
        destination_address: destination_address
      })
    ]

This seems to throw an error when generating the headers because buffer.pts is nil:

[error] <0.815.0>/:rtp/{:stream_send_bin, 1236}/:payloader/:header_generator Error handling action {:split, {:handle_buffer, [[:input, %Membrane.Buffer{payload: <<220, 255, 254>>, pts: nil, dts: nil, metadata: %{}}]]}} returned by callback Membrane.RTP.HeaderGenerator.handle_buffers_batch

[error] GenServer #PID<0.849.0> terminating
** (FunctionClauseError) no function clause matching in Ratio.mult/2
    (ratio 2.4.2) lib/ratio.ex:418: Ratio.mult(nil, 48000)
    (membrane_rtp_plugin 0.23.0) lib/membrane/rtp/header_generator.ex:71: Membrane.RTP.HeaderGenerator.handle_process/4

Does anyone have any tips on what I might be doing wrong?