Simple cleanups of AudioDecoder and AudioEncoder classes

webrtc/modules/audio_coding/codecs/pcm16b/audio_decoder_pcm16b.cc

 /*
  *  Copyright (c) 2015 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.
  */
 
 #include "webrtc/modules/audio_coding/codecs/pcm16b/include/audio_decoder_pcm16b.h"
 
 #include "webrtc/base/checks.h"
 #include "webrtc/modules/audio_coding/codecs/pcm16b/include/pcm16b.h"
 
 namespace webrtc {
 
-AudioDecoderPcm16B::AudioDecoderPcm16B() {}
+AudioDecoderPcm16B::AudioDecoderPcm16B(size_t num_channels)
+    : num_channels_(num_channels) {
+  RTC_DCHECK_GE(num_channels, 1u);
+}
 
 void AudioDecoderPcm16B::Reset() {}
 
 size_t AudioDecoderPcm16B::Channels() const {
-  return 1;
+  return num_channels_;
 }
 
 int AudioDecoderPcm16B::DecodeInternal(const uint8_t* encoded,
                                        size_t encoded_len,
                                        int sample_rate_hz,
                                        int16_t* decoded,
                                        SpeechType* speech_type) {
   RTC_DCHECK(sample_rate_hz == 8000 || sample_rate_hz == 16000 ||
              sample_rate_hz == 32000 || sample_rate_hz == 48000)
       << "Unsupported sample rate " << sample_rate_hz;
   size_t ret = WebRtcPcm16b_Decode(encoded, encoded_len, decoded);
   *speech_type = ConvertSpeechType(1);
   return static_cast<int>(ret);
 }
 
 int AudioDecoderPcm16B::PacketDuration(const uint8_t* encoded,
                                        size_t encoded_len) const {
   // Two encoded byte per sample per channel.
   return static_cast<int>(encoded_len / (2 * Channels()));
 }
 
-AudioDecoderPcm16BMultiCh::AudioDecoderPcm16BMultiCh(size_t num_channels)
-    : channels_(num_channels) {
-  RTC_DCHECK(num_channels > 0);
-}
-
-size_t AudioDecoderPcm16BMultiCh::Channels() const {
-  return channels_;
-}
-
 }  // namespace webrtc