Declare factory functions for video sender and receiver

Later CLs will switch to these functions, and eventually the
CreateMediaChannel will be deprecated and removed.

Bug: webrtc:13931
Change-Id: I4c5ab89659a47a501728cac217bb1a877fa50047
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/307800
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40221}

media/base/media_engine.h

@@ -163,6 +163,27 @@ class VideoEngineInterface : public RtpHeaderExtensionQueryInterface {
   VideoEngineInterface(const VideoEngineInterface&) = delete;
   VideoEngineInterface& operator=(const VideoEngineInterface&) = delete;
 
+  virtual std::unique_ptr<VideoMediaSendChannelInterface> CreateSendChannel(
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const VideoOptions& options,
+      const webrtc::CryptoOptions& crypto_options,
+      webrtc::VideoBitrateAllocatorFactory* video_bitrate_allocator_factory) {
+    // Default implementation, delete when all is updated
+    RTC_CHECK_NOTREACHED();
+    return nullptr;
+  }
+
+  virtual std::unique_ptr<VideoMediaReceiveChannelInterface>
+  CreateReceiveChannel(webrtc::Call* call,
+                       const MediaConfig& config,
+                       const VideoOptions& options,
+                       const webrtc::CryptoOptions& crypto_options) {
+    // Default implementation, delete when all is updated
+    RTC_CHECK_NOTREACHED();
+    return nullptr;
+  }
+
   // Creates a video media channel.
   // Returns NULL on failure.
   virtual VideoMediaChannel* CreateMediaChannel(

media/engine/webrtc_video_engine.cc

@@ -825,6 +825,27 @@ WebRtcVideoEngine::~WebRtcVideoEngine() {
   RTC_DLOG(LS_INFO) << "WebRtcVideoEngine::~WebRtcVideoEngine";
 }
 
+std::unique_ptr<VideoMediaSendChannelInterface>
+WebRtcVideoEngine::CreateSendChannel(
+    webrtc::Call* call,
+    const MediaConfig& config,
+    const VideoOptions& options,
+    const webrtc::CryptoOptions& crypto_options,
+    webrtc::VideoBitrateAllocatorFactory* video_bitrate_allocator_factory) {
+  return std::make_unique<WebRtcVideoSendChannel>(
+      call, config, options, crypto_options, encoder_factory_.get(),
+      decoder_factory_.get(), video_bitrate_allocator_factory);
+}
+std::unique_ptr<VideoMediaReceiveChannelInterface>
+WebRtcVideoEngine::CreateReceiveChannel(
+    webrtc::Call* call,
+    const MediaConfig& config,
+    const VideoOptions& options,
+    const webrtc::CryptoOptions& crypto_options) {
+  return std::make_unique<WebRtcVideoReceiveChannel>(
+      call, config, options, crypto_options, decoder_factory_.get());
+}
+
 VideoMediaChannel* WebRtcVideoEngine::CreateMediaChannel(
     MediaChannel::Role role,
     webrtc::Call* call,
@@ -836,14 +857,13 @@ VideoMediaChannel* WebRtcVideoEngine::CreateMediaChannel(
   std::unique_ptr<VideoMediaSendChannelInterface> send_channel;
   std::unique_ptr<VideoMediaReceiveChannelInterface> receive_channel;
   if (role == MediaChannel::Role::kSend || role == MediaChannel::Role::kBoth) {
-    send_channel = std::make_unique<WebRtcVideoSendChannel>(
-        call, config, options, crypto_options, encoder_factory_.get(),
-        decoder_factory_.get(), video_bitrate_allocator_factory);
+    send_channel = CreateSendChannel(call, config, options, crypto_options,
+                                     video_bitrate_allocator_factory);
   }
   if (role == MediaChannel::Role::kReceive ||
       role == MediaChannel::Role::kBoth) {
-    receive_channel = std::make_unique<WebRtcVideoReceiveChannel>(
-        call, config, options, crypto_options, decoder_factory_.get());
+    receive_channel =
+        CreateReceiveChannel(call, config, options, crypto_options);
   }
   return new VideoMediaShimChannel(std::move(send_channel),
                                    std::move(receive_channel));

media/engine/webrtc_video_engine.h

@@ -104,6 +104,19 @@ class WebRtcVideoEngine : public VideoEngineInterface {
 
   ~WebRtcVideoEngine() override;
 
+  std::unique_ptr<VideoMediaSendChannelInterface> CreateSendChannel(
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const VideoOptions& options,
+      const webrtc::CryptoOptions& crypto_options,
+      webrtc::VideoBitrateAllocatorFactory* video_bitrate_allocator_factory)
+      override;
+  std::unique_ptr<VideoMediaReceiveChannelInterface> CreateReceiveChannel(
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const VideoOptions& options,
+      const webrtc::CryptoOptions& crypto_options) override;
+
   VideoMediaChannel* CreateMediaChannel(
       MediaChannel::Role role,
       webrtc::Call* call,