Build WebRTC with data channel only.

webrtc/pc/mediasession.cc

 /*
  *  Copyright 2004 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 1248 matching lines @@
       add_legacy_(true),
       transport_desc_factory_(transport_desc_factory) {
 }
 
 MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
     ChannelManager* channel_manager,
     const TransportDescriptionFactory* transport_desc_factory)
     : secure_(SEC_DISABLED),
       add_legacy_(true),
       transport_desc_factory_(transport_desc_factory) {
+#ifdef HAVE_MEDIA
   channel_manager->GetSupportedAudioSendCodecs(&audio_send_codecs_);
   channel_manager->GetSupportedAudioReceiveCodecs(&audio_recv_codecs_);
   channel_manager->GetSupportedAudioRtpHeaderExtensions(&audio_rtp_extensions_);
   channel_manager->GetSupportedVideoCodecs(&video_codecs_);
   channel_manager->GetSupportedVideoRtpHeaderExtensions(&video_rtp_extensions_);
   channel_manager->GetSupportedDataCodecs(&data_codecs_);

[the sun, 2017/05/04 14:28:58]

Should this really be excluded?

[Zhi Huang, 2017/05/04 21:28:53]

This is because the |media_engine_| in channel manager in channelmanager is
nullptr. Another option would be adding nullptr checkers in these methods (if
media_engine == nullptr return;). Would that be better?

   NegotiateCodecs(audio_recv_codecs_, audio_send_codecs_,
                   &audio_sendrecv_codecs_);
+#endif
 }
 
 const AudioCodecs& MediaSessionDescriptionFactory::audio_sendrecv_codecs()
     const {
   return audio_sendrecv_codecs_;
 }
 
 const AudioCodecs& MediaSessionDescriptionFactory::audio_send_codecs() const {
   return audio_send_codecs_;
 }
@@ skipping 896 matching lines @@
       GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_VIDEO));
 }
 
 DataContentDescription* GetFirstDataContentDescription(
     SessionDescription* sdesc) {
   return static_cast<DataContentDescription*>(
       GetFirstMediaContentDescription(sdesc, MEDIA_TYPE_DATA));
 }
 
 }  // namespace cricket