Injectable audio encoders: voice_engine/channel changes.

webrtc/voice_engine/channel_proxy.h

Index: webrtc/voice_engine/channel_proxy.h
diff --git a/webrtc/voice_engine/channel_proxy.h b/webrtc/voice_engine/channel_proxy.h
index b70dcc454d0528e6fa0fb5ef26330ac4337abe58..29d71e16b8afd84196bc906c6a1ba249527bc710 100644
--- a/webrtc/voice_engine/channel_proxy.h
+++ b/webrtc/voice_engine/channel_proxy.h
@@ -15,6 +15,7 @@
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/race_checker.h"
 #include "webrtc/base/thread_checker.h"
+#include "webrtc/modules/audio_coding/codecs/audio_encoder_factory.h"
 #include "webrtc/voice_engine/channel_manager.h"
 #include "webrtc/voice_engine/include/voe_rtp_rtcp.h"
 
@@ -52,6 +53,10 @@ class ChannelProxy {
   explicit ChannelProxy(const ChannelOwner& channel_owner);
   virtual ~ChannelProxy();
 
+  virtual bool SetSendFormat(int payload_type,
+                             const SdpAudioFormat& format,
+                             AudioEncoderFactory* factory);

[the sun, 2017/02/22 14:08:38]

Why are we sending the factory all the way down here? Isn't it possible to
instantiate the encoder in WVoMC and pass it in AudioSendStream::Config?

[ossu, 2017/02/22 14:24:41]

Ah, yes: since we need the information from SdpAudioFormat to register the
payload with the RtpRtcpModule, we'd need to send along the SdpAudioFormat
anyway. To me, it seemed strange to send the encoder and the format together,
since they could theoretically be out-of-sync. This way, the format and audio
encoder will be as in-sync as the factory allows. We're at least not handing any
ownership over to Channel here.

I'm willing to entertain other variants, such as making it possible to query the
SdpAudioFormat from an AudioEncoder.

I believe this could be made clearer after an overhaul to the audio parts of the
RtpRtcpModule. I'm planning that as a follow-up to this (if only to remove its
use of CodecInst).

+
   virtual void SetRTCPStatus(bool enable);
   virtual void SetLocalSSRC(uint32_t ssrc);
   virtual void SetRTCP_CNAME(const std::string& c_name);