Posting Opus's set-force-channels functionality to WebRTC.

webrtc/modules/audio_coding/codecs/opus/opus_interface.h

 /*
  *  Copyright (c) 2012 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 177 matching lines @@
  *
  * Input:
  *      - inst               : Encoder context
  *      - complexity         : New target complexity (0-10, inclusive)
  *
  * Return value              :  0 - Success
  *                             -1 - Error
  */
 int16_t WebRtcOpus_SetComplexity(OpusEncInst* inst, int32_t complexity);
 
+/*
+ * WebRtcOpus_SetForceChannels(...)
+ *
+ * If the encoder is initialized as a stereo encoder, Opus will by default
+ * decide whether to encode in mono or stereo based on the bitrate. This
+ * function overrules the previous setting, and forces the encoder to encode
+ * in auto/mono/stereo.
+ *
+ * If the Encoder is initialized as a mono encoder, and one tries to force
+ * stereo, the function will return an error.
+ *
+ * Input:
+ *      - inst               : Encoder context
+ *      - num_channels       : 0 - Not forced
+ *                             1 - Mono
+ *                             2 - Stereo
+ *
+ * Return value              :  0 - Success
+ *                             -1 - Error
+ */
+int16_t WebRtcOpus_SetForceChannels(OpusEncInst* inst, int32_t num_channels);
+
 int16_t WebRtcOpus_DecoderCreate(OpusDecInst** inst, size_t channels);
 int16_t WebRtcOpus_DecoderFree(OpusDecInst* inst);
 
 /****************************************************************************
  * WebRtcOpus_DecoderChannels(...)
  *
  * This function returns the number of channels created for Opus decoder.
  */
 size_t WebRtcOpus_DecoderChannels(OpusDecInst* inst);
 
@@ skipping 132 matching lines @@
  *                                 1 - the packet contains FEC.
  */
 int WebRtcOpus_PacketHasFec(const uint8_t* payload,
                             size_t payload_length_bytes);
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_OPUS_OPUS_INTERFACE_H_