From 8f7866e60959bf3b05425ee895c51dd562ea8216 Mon Sep 17 00:00:00 2001
From: Jakub Pisarek <99591440+sgfn@users.noreply.github.com>
Date: Fri, 9 Aug 2024 12:57:09 +0200
Subject: [PATCH] Add behaviour and dynamic dispatch for (de)payloaders (#147)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Michał Śledź <michalsledz34@gmail.com>
---
 .../lib/save_to_file/peer_handler.ex          | 26 +++++++----
 .../lib/send_from_file/peer_handler.ex        | 11 +++--
 lib/ex_webrtc/rtp/depayloader.ex              | 42 +++++++++++++++++
 lib/ex_webrtc/rtp/depayloader_behaviour.ex    | 19 ++++++++
 lib/ex_webrtc/rtp/opus/depayloader.ex         | 32 ++++++++-----
 lib/ex_webrtc/rtp/opus/payloader.ex           | 30 +++++++-----
 lib/ex_webrtc/rtp/payloader.ex                | 46 +++++++++++++++++++
 lib/ex_webrtc/rtp/payloader_behaviour.ex      | 17 +++++++
 lib/ex_webrtc/rtp/vp8/depayloader.ex          | 38 +++++++--------
 lib/ex_webrtc/rtp/vp8/payload.ex              |  9 ++--
 lib/ex_webrtc/rtp/vp8/payloader.ex            | 39 ++++++++--------
 test/ex_webrtc/rtp/depayloader_test.exs       | 43 +++++++++++++++++
 test/ex_webrtc/rtp/payloader_test.exs         | 40 ++++++++++++++++
 test/ex_webrtc/rtp/vp8/depayloader_test.exs   | 25 +++++-----
 test/ex_webrtc/rtp/vp8/payloader_test.exs     |  6 +--
 15 files changed, 329 insertions(+), 94 deletions(-)
 create mode 100644 lib/ex_webrtc/rtp/depayloader.ex
 create mode 100644 lib/ex_webrtc/rtp/depayloader_behaviour.ex
 create mode 100644 lib/ex_webrtc/rtp/payloader.ex
 create mode 100644 lib/ex_webrtc/rtp/payloader_behaviour.ex
 create mode 100644 test/ex_webrtc/rtp/depayloader_test.exs
 create mode 100644 test/ex_webrtc/rtp/payloader_test.exs

diff --git a/examples/save_to_file/lib/save_to_file/peer_handler.ex b/examples/save_to_file/lib/save_to_file/peer_handler.ex
index b28373b..ca32a73 100644
--- a/examples/save_to_file/lib/save_to_file/peer_handler.ex
+++ b/examples/save_to_file/lib/save_to_file/peer_handler.ex
@@ -10,7 +10,7 @@ defmodule SaveToFile.PeerHandler do
   }
 
   alias ExWebRTC.Media.{IVF, Ogg}
-  alias ExWebRTC.RTP.{Opus, VP8}
+  alias ExWebRTC.RTP.Depayloader
 
   @behaviour WebSock
 
@@ -54,6 +54,7 @@ defmodule SaveToFile.PeerHandler do
       video_writer: nil,
       video_depayloader: nil,
       audio_writer: nil,
+      audio_depayloader: nil,
       frames_cnt: 0
     }
 
@@ -140,9 +141,11 @@ defmodule SaveToFile.PeerHandler do
         timebase_num: 1
       )
 
+    {:ok, video_depayloader} = @video_codecs |> hd() |> Depayloader.new()
+
     state = %{
       state
-      | video_depayloader: VP8.Depayloader.new(),
+      | video_depayloader: video_depayloader,
         video_writer: video_writer,
         video_track_id: id
     }
@@ -153,8 +156,15 @@ defmodule SaveToFile.PeerHandler do
   defp handle_webrtc_msg({:track, %MediaStreamTrack{kind: :audio, id: id}}, state) do
     # by default uses 1 mono channel and 48k clock rate
     {:ok, audio_writer} = Ogg.Writer.open(@audio_file)
+    {:ok, audio_depayloader} = @audio_codecs |> hd() |> Depayloader.new()
+
+    state = %{
+      state
+      | audio_depayloader: audio_depayloader,
+        audio_writer: audio_writer,
+        audio_track_id: id
+    }
 
-    state = %{state | audio_writer: audio_writer, audio_track_id: id}
     {:ok, state}
   end
 
@@ -166,11 +176,11 @@ defmodule SaveToFile.PeerHandler do
 
   defp handle_webrtc_msg({:rtp, id, nil, packet}, %{video_track_id: id} = state) do
     state =
-      case VP8.Depayloader.write(state.video_depayloader, packet) do
-        {:ok, video_depayloader} ->
+      case Depayloader.depayload(state.video_depayloader, packet) do
+        {nil, video_depayloader} ->
           %{state | video_depayloader: video_depayloader}
 
-        {:ok, vp8_frame, video_depayloader} ->
+        {vp8_frame, video_depayloader} ->
           frame = %IVF.Frame{timestamp: state.frames_cnt, data: vp8_frame}
           {:ok, video_writer} = IVF.Writer.write_frame(state.video_writer, frame)
 
@@ -186,10 +196,10 @@ defmodule SaveToFile.PeerHandler do
   end
 
   defp handle_webrtc_msg({:rtp, id, nil, packet}, %{audio_track_id: id} = state) do
-    opus_packet = Opus.Depayloader.depayload(packet)
+    {opus_packet, depayloader} = Depayloader.depayload(state.audio_depayloader, packet)
     {:ok, audio_writer} = Ogg.Writer.write_packet(state.audio_writer, opus_packet)
 
-    {:ok, %{state | audio_writer: audio_writer}}
+    {:ok, %{state | audio_depayloader: depayloader, audio_writer: audio_writer}}
   end
 
   defp handle_webrtc_msg(_msg, state), do: {:ok, state}
diff --git a/examples/send_from_file/lib/send_from_file/peer_handler.ex b/examples/send_from_file/lib/send_from_file/peer_handler.ex
index eeb37c2..02dbb37 100644
--- a/examples/send_from_file/lib/send_from_file/peer_handler.ex
+++ b/examples/send_from_file/lib/send_from_file/peer_handler.ex
@@ -12,7 +12,7 @@ defmodule SendFromFile.PeerHandler do
   }
 
   alias ExWebRTC.Media.{IVF, Ogg}
-  alias ExWebRTC.RTP.{Opus, VP8}
+  alias ExWebRTC.RTP.Payloader
 
   @behaviour WebSock
 
@@ -60,9 +60,10 @@ defmodule SendFromFile.PeerHandler do
     {:ok, _sender} = PeerConnection.add_track(pc, audio_track)
 
     {:ok, _header, video_reader} = IVF.Reader.open(@video_file)
-    video_payloader = VP8.Payloader.new(800)
+    {:ok, video_payloader} = @video_codecs |> hd() |> Payloader.new(max_payload_size: 800)
 
     {:ok, audio_reader} = Ogg.Reader.open(@audio_file)
+    {:ok, audio_payloader} = @audio_codecs |> hd() |> Payloader.new()
 
     state = %{
       peer_connection: pc,
@@ -71,6 +72,7 @@ defmodule SendFromFile.PeerHandler do
       video_reader: video_reader,
       video_payloader: video_payloader,
       audio_reader: audio_reader,
+      audio_payloader: audio_payloader,
       next_video_timestamp: Enum.random(0..@max_rtp_timestamp),
       next_audio_timestamp: Enum.random(0..@max_rtp_timestamp),
       next_video_sequence_number: Enum.random(0..@max_rtp_seq_no),
@@ -112,7 +114,7 @@ defmodule SendFromFile.PeerHandler do
 
     case IVF.Reader.next_frame(state.video_reader) do
       {:ok, frame} ->
-        {rtp_packets, payloader} = VP8.Payloader.payload(state.video_payloader, frame.data)
+        {rtp_packets, payloader} = Payloader.payload(state.video_payloader, frame.data)
 
         # 3_000 = 90_000 (VP8 clock rate) / 30 FPS
         next_sequence_number =
@@ -158,7 +160,7 @@ defmodule SendFromFile.PeerHandler do
         # and time spent on reading and parsing the file
         Process.send_after(self(), :send_audio, duration)
 
-        rtp_packet = Opus.Payloader.payload(packet)
+        {[rtp_packet], payloader} = Payloader.payload(state.audio_payloader, packet)
 
         rtp_packet = %{
           rtp_packet
@@ -177,6 +179,7 @@ defmodule SendFromFile.PeerHandler do
         state = %{
           state
           | audio_reader: reader,
+            audio_payloader: payloader,
             next_audio_timestamp: next_timestamp,
             next_audio_sequence_number: next_sequence_number
         }
diff --git a/lib/ex_webrtc/rtp/depayloader.ex b/lib/ex_webrtc/rtp/depayloader.ex
new file mode 100644
index 0000000..33f0cce
--- /dev/null
+++ b/lib/ex_webrtc/rtp/depayloader.ex
@@ -0,0 +1,42 @@
+defmodule ExWebRTC.RTP.Depayloader do
+  @moduledoc """
+  RTP depayloader.
+
+  It unpacks RTP pakcets into audio/video frames.
+  """
+
+  alias ExWebRTC.RTPCodecParameters
+
+  @opaque depayloader :: struct()
+
+  @doc """
+  Creates a new depayloader that matches the passed codec parameters.
+  """
+  @spec new(RTPCodecParameters.t()) ::
+          {:ok, depayloader()} | {:error, :no_depayloader_for_codec}
+  def new(codec_params) do
+    with {:ok, module} <- to_depayloader_module(codec_params.mime_type) do
+      depayloader = module.new()
+      {:ok, depayloader}
+    end
+  end
+
+  @doc """
+  Processes binary data from a single RTP packet, and outputs a frame if assembled.
+
+  Returns the frame (or `nil` if a frame could not be depayloaded yet)
+  together with the updated depayloader.
+  """
+  @spec depayload(depayloader(), ExRTP.Packet.t()) :: {binary() | nil, depayloader()}
+  def depayload(%module{} = depayloader, packet) do
+    module.depayload(depayloader, packet)
+  end
+
+  defp to_depayloader_module(mime_type) do
+    case String.downcase(mime_type) do
+      "video/vp8" -> {:ok, ExWebRTC.RTP.Depayloader.VP8}
+      "audio/opus" -> {:ok, ExWebRTC.RTP.Depayloader.Opus}
+      _other -> {:error, :no_depayloader_for_codec}
+    end
+  end
+end
diff --git a/lib/ex_webrtc/rtp/depayloader_behaviour.ex b/lib/ex_webrtc/rtp/depayloader_behaviour.ex
new file mode 100644
index 0000000..3bae5cf
--- /dev/null
+++ b/lib/ex_webrtc/rtp/depayloader_behaviour.ex
@@ -0,0 +1,19 @@
+defmodule ExWebRTC.RTP.Depayloader.Behaviour do
+  @moduledoc false
+
+  @type depayloader :: struct()
+
+  @doc """
+  Creates a new depayloader struct.
+  """
+  @callback new() :: depayloader()
+
+  @doc """
+  Processes binary data from a single RTP packet, and outputs a frame if assembled.
+
+  Returns the frame (or `nil` if a frame could not be depayloaded yet)
+  together with the updated depayloader struct.
+  """
+  @callback depayload(depayloader(), packet :: ExRTP.Packet.t()) ::
+              {binary() | nil, depayloader()}
+end
diff --git a/lib/ex_webrtc/rtp/opus/depayloader.ex b/lib/ex_webrtc/rtp/opus/depayloader.ex
index ad89c5b..38b75c8 100644
--- a/lib/ex_webrtc/rtp/opus/depayloader.ex
+++ b/lib/ex_webrtc/rtp/opus/depayloader.ex
@@ -1,15 +1,25 @@
-defmodule ExWebRTC.RTP.Opus.Depayloader do
-  @moduledoc """
-  Decapsualtes Opus audio out of RTP packet.
-
-  Based on [RFC 7587: RTP Payload Format for the Opus Speech and Audio Codec](https://datatracker.ietf.org/doc/html/rfc7587).
-  """
+defmodule ExWebRTC.RTP.Depayloader.Opus do
+  @moduledoc false
+  # Decapsualtes Opus audio out of RTP packet.
+  #
+  # Based on [RFC 7587: RTP Payload Format for the Opus Speech and Audio Codec](https://datatracker.ietf.org/doc/html/rfc7587).
 
   alias ExRTP.Packet
 
-  @doc """
-  Takes Opus packet out of an RTP packet.
-  """
-  @spec depayload(Packet.t()) :: binary()
-  def depayload(%Packet{payload: payload}), do: payload
+  @behaviour ExWebRTC.RTP.Depayloader.Behaviour
+
+  @type t :: %__MODULE__{}
+
+  defstruct []
+
+  @impl true
+  @spec new() :: t()
+  def new() do
+    %__MODULE__{}
+  end
+
+  @impl true
+  @spec depayload(t(), Packet.t()) :: {binary(), t()}
+  def depayload(%__MODULE__{} = depayloader, %Packet{payload: payload}),
+    do: {payload, depayloader}
 end
diff --git a/lib/ex_webrtc/rtp/opus/payloader.ex b/lib/ex_webrtc/rtp/opus/payloader.ex
index ef1f3f7..a0e8215 100644
--- a/lib/ex_webrtc/rtp/opus/payloader.ex
+++ b/lib/ex_webrtc/rtp/opus/payloader.ex
@@ -1,17 +1,23 @@
-defmodule ExWebRTC.RTP.Opus.Payloader do
-  @moduledoc """
-  Encapsulates Opus audio packet into an RTP packet.
+defmodule ExWebRTC.RTP.Payloader.Opus do
+  @moduledoc false
+  # Encapsulates Opus audio packet into an RTP packet.
+  #
+  # Based on [RFC 7587: RTP Payload Format for the Opus Speech and Audio Codec](https://datatracker.ietf.org/doc/html/rfc7587).
 
-  Based on [RFC 7587: RTP Payload Format for the Opus Speech and Audio Codec](https://datatracker.ietf.org/doc/html/rfc7587).
-  """
+  @behaviour ExWebRTC.RTP.Payloader.Behaviour
 
-  @doc """
-  Packs Opus packet into an RTP packet.
+  @type t :: %__MODULE__{}
 
-  Fields from RTP header like ssrc, timestamp etc. are set to 0.
-  """
-  @spec payload(binary()) :: ExRTP.Packet.t()
-  def payload(packet) when packet != <<>> do
-    ExRTP.Packet.new(packet)
+  defstruct []
+
+  @impl true
+  def new(_max_payload_size) do
+    %__MODULE__{}
+  end
+
+  @impl true
+  @spec payload(t(), binary()) :: {[ExRTP.Packet.t()], t()}
+  def payload(%__MODULE__{} = payloader, packet) when packet != <<>> do
+    {[ExRTP.Packet.new(packet)], payloader}
   end
 end
diff --git a/lib/ex_webrtc/rtp/payloader.ex b/lib/ex_webrtc/rtp/payloader.ex
new file mode 100644
index 0000000..08ac1e3
--- /dev/null
+++ b/lib/ex_webrtc/rtp/payloader.ex
@@ -0,0 +1,46 @@
+defmodule ExWebRTC.RTP.Payloader do
+  @moduledoc """
+  RTP payloader.
+
+  It packs audio/video frames into one or more RTP packets.
+  """
+
+  alias ExWebRTC.RTPCodecParameters
+
+  @opaque payloader :: struct()
+
+  @doc """
+  Creates a new payloader that matches the passed codec parameters.
+
+  Opts:
+    * max_payload_size - determines the maximum size of a single RTP packet outputted by the payloader.
+    It must be greater than `100`, and is set to `1000` by default.
+  """
+  @spec new(RTPCodecParameters.t(), max_payload_size: integer()) ::
+          {:ok, payloader()} | {:error, :no_payloader_for_codec}
+  def new(codec_params, opts \\ []) do
+    with {:ok, module} <- to_payloader_module(codec_params.mime_type) do
+      max_payload_size = opts[:max_payload_size] || 1000
+      payloader = module.new(max_payload_size)
+      {:ok, payloader}
+    end
+  end
+
+  @doc """
+  Packs a frame into one or more RTP packets.
+
+  Returns the packets together with the updated payloader.
+  """
+  @spec payload(payloader(), binary()) :: {[ExRTP.Packet.t()], payloader()}
+  def payload(%module{} = payloader, frame) do
+    module.payload(payloader, frame)
+  end
+
+  defp to_payloader_module(mime_type) do
+    case String.downcase(mime_type) do
+      "video/vp8" -> {:ok, ExWebRTC.RTP.Payloader.VP8}
+      "audio/opus" -> {:ok, ExWebRTC.RTP.Payloader.Opus}
+      _other -> {:error, :no_payloader_for_codec}
+    end
+  end
+end
diff --git a/lib/ex_webrtc/rtp/payloader_behaviour.ex b/lib/ex_webrtc/rtp/payloader_behaviour.ex
new file mode 100644
index 0000000..81c3df4
--- /dev/null
+++ b/lib/ex_webrtc/rtp/payloader_behaviour.ex
@@ -0,0 +1,17 @@
+defmodule ExWebRTC.RTP.Payloader.Behaviour do
+  @moduledoc false
+
+  @type payloader :: struct()
+
+  @doc """
+  Creates a new payloader struct.
+  """
+  @callback new(max_payload_size :: integer()) :: payloader()
+
+  @doc """
+  Packs a frame into one or more RTP packets.
+
+  Returns the packets together with the updated payloader struct.
+  """
+  @callback payload(payloader(), frame :: binary()) :: {[ExRTP.Packet.t()], payloader()}
+end
diff --git a/lib/ex_webrtc/rtp/vp8/depayloader.ex b/lib/ex_webrtc/rtp/vp8/depayloader.ex
index c56cf15..42b6b2c 100644
--- a/lib/ex_webrtc/rtp/vp8/depayloader.ex
+++ b/lib/ex_webrtc/rtp/vp8/depayloader.ex
@@ -1,34 +1,36 @@
-defmodule ExWebRTC.RTP.VP8.Depayloader do
-  @moduledoc """
-  Reassembles VP8 frames from RTP packets.
+defmodule ExWebRTC.RTP.Depayloader.VP8 do
+  @moduledoc false
+  # Reassembles VP8 frames from RTP packets.
+  #
+  # Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
+
+  @behaviour ExWebRTC.RTP.Depayloader.Behaviour
 
-  Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
-  """
   require Logger
 
   alias ExWebRTC.RTP.VP8.Payload
 
-  @opaque t() :: %__MODULE__{
-            current_frame: nil,
-            current_timestamp: nil
-          }
+  @type t() :: %__MODULE__{
+          current_frame: nil,
+          current_timestamp: nil
+        }
 
   defstruct [:current_frame, :current_timestamp]
 
-  @spec new() :: t()
+  @impl true
   def new() do
     %__MODULE__{}
   end
 
-  @spec write(t(), ExRTP.Packet.t()) :: {:ok, t()} | {:ok, binary(), t()}
-  def write(depayloader, packet)
+  @impl true
+  def depayload(depayloader, packet)
 
-  def write(depayloader, %ExRTP.Packet{payload: <<>>, padding: true}), do: {:ok, depayloader}
+  def depayload(depayloader, %ExRTP.Packet{payload: <<>>, padding: true}), do: {nil, depayloader}
 
-  def write(depayloader, packet) do
+  def depayload(depayloader, packet) do
     case Payload.parse(packet.payload) do
       {:ok, vp8_payload} ->
-        do_write(depayloader, packet, vp8_payload)
+        do_depayload(depayloader, packet, vp8_payload)
 
       {:error, reason} ->
         Logger.warning("""
@@ -40,7 +42,7 @@ defmodule ExWebRTC.RTP.VP8.Depayloader do
     end
   end
 
-  defp do_write(depayloader, packet, vp8_payload) do
+  defp do_depayload(depayloader, packet, vp8_payload) do
     depayloader =
       case {depayloader.current_frame, vp8_payload} do
         {nil, %Payload{s: 1, pid: 0}} ->
@@ -80,10 +82,10 @@ defmodule ExWebRTC.RTP.VP8.Depayloader do
 
     case {depayloader.current_frame, packet.marker} do
       {current_frame, true} when current_frame != nil ->
-        {:ok, current_frame, %{depayloader | current_frame: nil, current_timestamp: nil}}
+        {current_frame, %{depayloader | current_frame: nil, current_timestamp: nil}}
 
       _ ->
-        {:ok, depayloader}
+        {nil, depayloader}
     end
   end
 end
diff --git a/lib/ex_webrtc/rtp/vp8/payload.ex b/lib/ex_webrtc/rtp/vp8/payload.ex
index 48338f0..eb74684 100644
--- a/lib/ex_webrtc/rtp/vp8/payload.ex
+++ b/lib/ex_webrtc/rtp/vp8/payload.ex
@@ -1,9 +1,8 @@
 defmodule ExWebRTC.RTP.VP8.Payload do
-  @moduledoc """
-  Defines VP8 payload structure stored in RTP packet payload.
-
-  Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
-  """
+  @moduledoc false
+  # Defines VP8 payload structure stored in RTP packet payload.
+  #
+  # Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
 
   @type t() :: %__MODULE__{
           n: 0 | 1,
diff --git a/lib/ex_webrtc/rtp/vp8/payloader.ex b/lib/ex_webrtc/rtp/vp8/payloader.ex
index 27b24d1..bcf374e 100644
--- a/lib/ex_webrtc/rtp/vp8/payloader.ex
+++ b/lib/ex_webrtc/rtp/vp8/payloader.ex
@@ -1,12 +1,13 @@
-defmodule ExWebRTC.RTP.VP8.Payloader do
-  @moduledoc """
-  Encapsulates VP8 video frames into RTP packets.
+defmodule ExWebRTC.RTP.Payloader.VP8 do
+  @moduledoc false
+  # Encapsulates VP8 video frames into RTP packets.
+  #
+  # Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
+  #
+  # It does not support `X` bit right now, in particular it
+  # does not pay attention to VP8 partition boundaries (see RFC 7741 sec. 4.4).
 
-  Based on [RFC 7741: RTP Payload Format for VP8 Video](https://datatracker.ietf.org/doc/html/rfc7741).
-
-  It does not support `X` bit right now, in particular it
-  does not pay attention to VP8 partition boundaries (see RFC 7741 sec. 4.4).
-  """
+  @behaviour ExWebRTC.RTP.Payloader.Behaviour
 
   @first_chunk_descriptor <<0::1, 0::1, 0::1, 1::1, 0::1, 0::3>>
 
@@ -14,24 +15,20 @@ defmodule ExWebRTC.RTP.VP8.Payloader do
 
   @desc_size_bytes 1
 
-  @opaque t() :: %__MODULE__{
-            max_payload_size: non_neg_integer()
-          }
+  @type t() :: %__MODULE__{
+          max_payload_size: non_neg_integer()
+        }
 
-  defstruct [:max_payload_size]
+  @enforce_keys [:max_payload_size]
+  defstruct @enforce_keys
 
-  @spec new(non_neg_integer()) :: t()
-  def new(max_payload_size \\ 1000) when max_payload_size > 100 do
+  @impl true
+  def new(max_payload_size) when max_payload_size > 100 do
     %__MODULE__{max_payload_size: max_payload_size}
   end
 
-  @doc """
-  Packs VP8 frame into one or more RTP packets.
-
-  Fields from RTP header like ssrc, timestamp etc. are set to 0.
-  """
-  @spec payload(t(), frame :: binary()) :: {[ExRTP.Packet.t()], t()}
-  def payload(payloader, frame) when frame != <<>> do
+  @impl true
+  def payload(%__MODULE__{} = payloader, frame) when frame != <<>> do
     rtp_payloads = chunk(frame, payloader.max_payload_size - @desc_size_bytes)
 
     [first_rtp_payload | next_rtp_payloads] = rtp_payloads
diff --git a/test/ex_webrtc/rtp/depayloader_test.exs b/test/ex_webrtc/rtp/depayloader_test.exs
new file mode 100644
index 0000000..01c35be
--- /dev/null
+++ b/test/ex_webrtc/rtp/depayloader_test.exs
@@ -0,0 +1,43 @@
+defmodule ExWebRTC.RTP.DepayloaderTest do
+  use ExUnit.Case, async: true
+
+  alias ExWebRTC.RTPCodecParameters
+  alias ExWebRTC.RTP.Depayloader
+
+  @packet %ExRTP.Packet{
+    payload_type: 96,
+    sequence_number: 0,
+    timestamp: 0,
+    ssrc: 0,
+    payload: <<0, 1, 2, 3>>
+  }
+
+  test "creates a VP8 depayloader and dispatches calls to its module" do
+    assert {:ok, depayloader} =
+             %RTPCodecParameters{payload_type: 96, mime_type: "video/VP8", clock_rate: 90_000}
+             |> Depayloader.new()
+
+    assert Depayloader.depayload(depayloader, @packet) ==
+             Depayloader.VP8.depayload(depayloader, @packet)
+  end
+
+  test "creates an Opus depayloader and dispatches calls to its module" do
+    assert {:ok, depayloader} =
+             %RTPCodecParameters{
+               payload_type: 96,
+               mime_type: "audio/opus",
+               clock_rate: 48_000,
+               channels: 2
+             }
+             |> Depayloader.new()
+
+    assert Depayloader.depayload(depayloader, @packet) ==
+             Depayloader.Opus.depayload(depayloader, @packet)
+  end
+
+  test "returns error if no depayloader exists for given codec" do
+    assert {:error, :no_depayloader_for_codec} =
+             %RTPCodecParameters{payload_type: 97, mime_type: "video/H264", clock_rate: 90_000}
+             |> Depayloader.new()
+  end
+end
diff --git a/test/ex_webrtc/rtp/payloader_test.exs b/test/ex_webrtc/rtp/payloader_test.exs
new file mode 100644
index 0000000..ea7fd76
--- /dev/null
+++ b/test/ex_webrtc/rtp/payloader_test.exs
@@ -0,0 +1,40 @@
+defmodule ExWebRTC.RTP.PayloaderTest do
+  use ExUnit.Case, async: true
+
+  alias ExWebRTC.RTPCodecParameters
+  alias ExWebRTC.RTP.Payloader
+
+  @frame <<0, 1, 2, 3>>
+
+  test "creates a VP8 payloader and dispatches calls to its module" do
+    assert {:ok, _payloader} =
+             %RTPCodecParameters{payload_type: 96, mime_type: "video/VP8", clock_rate: 90_000}
+             |> Payloader.new()
+
+    # with options
+    assert {:ok, payloader} =
+             %RTPCodecParameters{payload_type: 96, mime_type: "video/VP8", clock_rate: 90_000}
+             |> Payloader.new(max_payload_size: 800)
+
+    assert Payloader.payload(payloader, @frame) == Payloader.VP8.payload(payloader, @frame)
+  end
+
+  test "creates an Opus payloader and dispatches calls to its module" do
+    assert {:ok, payloader} =
+             %RTPCodecParameters{
+               payload_type: 111,
+               mime_type: "audio/opus",
+               clock_rate: 48_000,
+               channels: 2
+             }
+             |> Payloader.new()
+
+    assert Payloader.payload(payloader, @frame) == Payloader.Opus.payload(payloader, @frame)
+  end
+
+  test "returns error if no payloader exists for given codec" do
+    assert {:error, :no_payloader_for_codec} =
+             %RTPCodecParameters{payload_type: 97, mime_type: "video/H264", clock_rate: 90_000}
+             |> Payloader.new()
+  end
+end
diff --git a/test/ex_webrtc/rtp/vp8/depayloader_test.exs b/test/ex_webrtc/rtp/vp8/depayloader_test.exs
index 7ff1c46..ff65619 100644
--- a/test/ex_webrtc/rtp/vp8/depayloader_test.exs
+++ b/test/ex_webrtc/rtp/vp8/depayloader_test.exs
@@ -1,10 +1,11 @@
 defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
   use ExUnit.Case, async: true
 
-  alias ExWebRTC.RTP.VP8.{Payload, Depayloader}
+  alias ExWebRTC.RTP.Depayloader
+  alias ExWebRTC.RTP.VP8.Payload
 
   test "write/2" do
-    depayloader = Depayloader.new()
+    depayloader = Depayloader.VP8.new()
     # random vp8 data, not necessarily correct
     data = <<0, 1, 2, 3>>
 
@@ -14,8 +15,8 @@ defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
 
     packet = ExRTP.Packet.new(vp8_payload, marker: true)
 
-    assert {:ok, ^data, %{current_frame: nil, current_timestamp: nil} = depayloader} =
-             Depayloader.write(depayloader, packet)
+    assert {^data, %{current_frame: nil, current_timestamp: nil} = depayloader} =
+             Depayloader.VP8.depayload(depayloader, packet)
 
     # packet that doesn't start a new frame
     vp8_payload = %Payload{n: 0, s: 0, pid: 0, payload: data}
@@ -23,8 +24,8 @@ defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
 
     packet = ExRTP.Packet.new(vp8_payload)
 
-    assert {:ok, %{current_frame: nil, current_timestamp: nil} = depayloader} =
-             Depayloader.write(depayloader, packet)
+    assert {nil, %{current_frame: nil, current_timestamp: nil} = depayloader} =
+             Depayloader.VP8.depayload(depayloader, packet)
 
     # packet that starts a new frame without finishing the previous one
     vp8_payload = %Payload{n: 0, s: 1, pid: 0, payload: data}
@@ -32,8 +33,8 @@ defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
 
     packet = ExRTP.Packet.new(vp8_payload)
 
-    assert {:ok, %{current_frame: ^data, current_timestamp: 0} = depayloader} =
-             Depayloader.write(depayloader, packet)
+    assert {nil, %{current_frame: ^data, current_timestamp: 0} = depayloader} =
+             Depayloader.VP8.depayload(depayloader, packet)
 
     data2 = data <> <<0>>
     vp8_payload = %Payload{n: 0, s: 1, pid: 0, payload: data2}
@@ -41,8 +42,8 @@ defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
 
     packet = ExRTP.Packet.new(vp8_payload, timestamp: 3000)
 
-    assert {:ok, %{current_frame: ^data2, current_timestamp: 3000} = depayloader} =
-             Depayloader.write(depayloader, packet)
+    assert {nil, %{current_frame: ^data2, current_timestamp: 3000} = depayloader} =
+             Depayloader.VP8.depayload(depayloader, packet)
 
     # packet with timestamp from a new frame that is not a beginning of this frame
     data2 = data
@@ -51,7 +52,7 @@ defmodule ExWebRTC.RTP.VP8.DepayloaderTest do
 
     packet = ExRTP.Packet.new(vp8_payload, timestamp: 6000)
 
-    assert {:ok, %{current_frame: nil, current_timestamp: nil}} =
-             Depayloader.write(depayloader, packet)
+    assert {nil, %{current_frame: nil, current_timestamp: nil}} =
+             Depayloader.VP8.depayload(depayloader, packet)
   end
 end
diff --git a/test/ex_webrtc/rtp/vp8/payloader_test.exs b/test/ex_webrtc/rtp/vp8/payloader_test.exs
index cd64260..3721715 100644
--- a/test/ex_webrtc/rtp/vp8/payloader_test.exs
+++ b/test/ex_webrtc/rtp/vp8/payloader_test.exs
@@ -2,17 +2,17 @@ defmodule ExWebRTC.RTP.VP8.PayloaderTest do
   use ExUnit.Case, async: true
 
   alias ExWebRTC.Media.IVF.Reader
-  alias ExWebRTC.RTP.VP8.Payloader
+  alias ExWebRTC.RTP.Payloader
 
   test "payload vp8 video" do
     # video frames in the fixture are mostly 500+ bytes
-    vp8_payloader = Payloader.new(200)
+    vp8_payloader = Payloader.VP8.new(200)
     {:ok, _header, ivf_reader} = Reader.open("test/fixtures/ivf/vp8_correct.ivf")
 
     for _i <- 0..28, reduce: vp8_payloader do
       vp8_payloader ->
         {:ok, frame} = Reader.next_frame(ivf_reader)
-        {rtp_packets, vp8_payloader} = Payloader.payload(vp8_payloader, frame.data)
+        {rtp_packets, vp8_payloader} = Payloader.VP8.payload(vp8_payloader, frame.data)
 
         # assert all packets but last are 200 bytes
         rtp_packets