Injectable audio encoders: BuiltinAudioEncoderFactory

webrtc/api/audio_codecs/audio_format.h

 /*
  *  Copyright (c) 2016 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.
  */
 
 #ifndef WEBRTC_API_AUDIO_CODECS_AUDIO_FORMAT_H_
 #define WEBRTC_API_AUDIO_CODECS_AUDIO_FORMAT_H_
 
 #include <map>
 #include <ostream>
 #include <string>
 #include <utility>
 
+#include "webrtc/base/optional.h"
+
 namespace webrtc {
 
 // SDP specification for a single audio codec.
 // NOTE: This class is still under development and may change without notice.
 struct SdpAudioFormat {
   using Parameters = std::map<std::string, std::string>;
 
   SdpAudioFormat(const SdpAudioFormat&);
   SdpAudioFormat(SdpAudioFormat&&);
-  SdpAudioFormat(const char* name, int clockrate_hz, int num_channels);
-  SdpAudioFormat(const std::string& name, int clockrate_hz, int num_channels);
+  SdpAudioFormat(const char* name, int clockrate_hz, size_t num_channels);
+  SdpAudioFormat(const std::string& name,
+                 int clockrate_hz,
+                 size_t num_channels);
   SdpAudioFormat(const char* name,
                  int clockrate_hz,
-                 int num_channels,
+                 size_t num_channels,
                  const Parameters& param);
   SdpAudioFormat(const std::string& name,
                  int clockrate_hz,
-                 int num_channels,
+                 size_t num_channels,
                  const Parameters& param);
   ~SdpAudioFormat();
 
   SdpAudioFormat& operator=(const SdpAudioFormat&);
   SdpAudioFormat& operator=(SdpAudioFormat&&);
 
   friend bool operator==(const SdpAudioFormat& a, const SdpAudioFormat& b);
   friend bool operator!=(const SdpAudioFormat& a, const SdpAudioFormat& b) {
     return !(a == b);
   }
 
   std::string name;
   int clockrate_hz;
-  int num_channels;
+  size_t num_channels;
   Parameters parameters;
 };
 
 void swap(SdpAudioFormat& a, SdpAudioFormat& b);
 std::ostream& operator<<(std::ostream& os, const SdpAudioFormat& saf);
 
-// To avoid API breakage, and make the code clearer, AudioCodecSpec should not
+// Information about how an audio format is treated by the codec implementation.
+// Contains basic information, such as sample rate and number of channels, which
+// isn't uniformly presented by SDP. Also contains flags indicating support for
+// integrating with other parts of WebRTC, like external VAD and comfort noise
+// level calculation.
+//
+// To avoid API breakage, and make the code clearer, AudioCodecInfo should not
 // be directly initializable with any flags indicating optional support. If it
 // were, these initializers would break any time a new flag was added. It's also
 // more difficult to understand:
-//   AudioCodecSpec spec{{"format", 8000, 1}, true, false, false, true, true};
+//   AudioCodecInfo info{16000, 1, 32000, true, false, false, true, true};
 // than
-//   AudioCodecSpec spec({"format", 8000, 1});
-//   spec.allow_comfort_noise = true;
-//   spec.future_flag_b = true;
-//   spec.future_flag_c = true;
-struct AudioCodecSpec {
-  explicit AudioCodecSpec(const SdpAudioFormat& format);
-  explicit AudioCodecSpec(SdpAudioFormat&& format);
-  ~AudioCodecSpec() = default;
+//   AudioCodecInfo info(16000, 1, 32000);
+//   info.allow_comfort_noise = true;
+//   info.future_flag_b = true;
+//   info.future_flag_c = true;
+struct AudioCodecInfo {
+  AudioCodecInfo(int sample_rate_hz, size_t num_channels, int bitrate_bps);
+  AudioCodecInfo(int sample_rate_hz,
+                 size_t num_channels,
+                 int default_bitrate_bps,
+                 int min_bitrate_bps,
+                 int max_bitrate_bps);
+  AudioCodecInfo(const AudioCodecInfo& b) = default;
+  ~AudioCodecInfo() = default;
 
-  SdpAudioFormat format;
+  bool operator==(const AudioCodecInfo& b) const {
+    return sample_rate_hz == b.sample_rate_hz &&
+           num_channels == b.num_channels &&
+           default_bitrate_bps == b.default_bitrate_bps &&
+           min_bitrate_bps == b.min_bitrate_bps &&
+           max_bitrate_bps == b.max_bitrate_bps &&
+           allow_comfort_noise == b.allow_comfort_noise &&
+           supports_network_adaption == b.supports_network_adaption;
+  }
+
+  bool operator!=(const AudioCodecInfo& b) const { return !(*this == b); }
+
+  bool HasFixedBitrate() const {
+    RTC_DCHECK_GE(min_bitrate_bps, 0);
+    RTC_DCHECK_LE(min_bitrate_bps, default_bitrate_bps);
+    RTC_DCHECK_GE(max_bitrate_bps, default_bitrate_bps);
+    return min_bitrate_bps == max_bitrate_bps;
+  }
+
+  int sample_rate_hz;
+  size_t num_channels;
+  int default_bitrate_bps;
+  int min_bitrate_bps;
+  int max_bitrate_bps;
+
   bool allow_comfort_noise = true;  // This codec can be used with an external
                                     // comfort noise generator.
   bool supports_network_adaption = false;  // This codec can adapt to varying
                                            // network conditions.
 };
 
+// AudioCodecSpec ties an audio format to specific information about the codec
+// and its implementation.
+struct AudioCodecSpec {
+  bool operator==(const AudioCodecSpec& b) const {
+    return format == b.format && info == b.info;
+  }
+
+  bool operator!=(const AudioCodecSpec& b) const { return !(*this == b); }
+
+  SdpAudioFormat format;
+  AudioCodecInfo info;
+};
+
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_AUDIO_CODECS_AUDIO_FORMAT_H_