Split audio mixer into interface and implementation.

The AudioMixer is now split in a mixer and audio source interface part, which has moved to webrtc/api, and a default implementation part, which lies in webrtc/modules.

This change makes it possible to create other mixer implementations and is a first step to facilitate passing down a mixer from outside of WebRTC.

It will also create less build dependencies when the new mixer has replaced the old one.

NOTRY=True
TBR=henrik.lundin@webrtc.org
BUG=webrtc:6346

Review-Url: https://codereview.webrtc.org/2411313003
Cr-Commit-Position: refs/heads/master@{#14705}
diff --git a/.gn b/.gn
index 7a98fad..4aa7a76 100644
--- a/.gn
+++ b/.gn
@@ -20,6 +20,7 @@
 # "gn check" or "gn gen --check".
 # TODO(kjellander): Keep adding paths to this list as work in webrtc:5589 is done.
 check_targets = [
+  "//webrtc/api:audio_mixer_api",
   "//webrtc/api:rtc_stats_api",
   "//webrtc/modules/audio_coding:g711_test",
   "//webrtc/modules/audio_coding:g722_test",
diff --git a/webrtc/api/BUILD.gn b/webrtc/api/BUILD.gn
index 6de99f7..6424de9 100644
--- a/webrtc/api/BUILD.gn
+++ b/webrtc/api/BUILD.gn
@@ -321,6 +321,17 @@
   ]
 }
 
+# GYP version: webrtc/api/api.gyp:audio_mixer_api
+rtc_source_set("audio_mixer_api") {
+  sources = [
+    "audio/audio_mixer.h",
+  ]
+
+  deps = [
+    "../base:rtc_base_approved",
+  ]
+}
+
 if (rtc_include_tests) {
   config("peerconnection_unittests_config") {
     # The warnings below are enabled by default. Since GN orders compiler flags
diff --git a/webrtc/api/api.gyp b/webrtc/api/api.gyp
index c431e9e..8a7fe5a 100644
--- a/webrtc/api/api.gyp
+++ b/webrtc/api/api.gyp
@@ -232,5 +232,16 @@
         'stats/rtcstatsreport.h',
       ],
     },  # target rtc_stats_api
+    {
+      # GN version: webrtc/api:audio_mixer_api
+      'target_name': 'audio_mixer_api',
+      'type': 'static_library',
+      'dependencies': [
+        '<(webrtc_root)/base/base.gyp:rtc_base_approved',
+      ],
+      'sources': [
+        'audio/audio_mixer.h',
+      ],
+    },  # target rtc_stats_api
   ],  # targets
 }
diff --git a/webrtc/modules/audio_mixer/audio_mixer.h b/webrtc/api/audio/audio_mixer.h
similarity index 81%
rename from webrtc/modules/audio_mixer/audio_mixer.h
rename to webrtc/api/audio/audio_mixer.h
index 7e58a8d..960adbb 100644
--- a/webrtc/modules/audio_mixer/audio_mixer.h
+++ b/webrtc/api/audio/audio_mixer.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_
-#define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_
+#ifndef WEBRTC_API_AUDIO_AUDIO_MIXER_H_
+#define WEBRTC_API_AUDIO_AUDIO_MIXER_H_
 
 #include <memory>
 
@@ -18,6 +18,9 @@
 
 namespace webrtc {
 
+// WORK IN PROGRESS
+// This class is under development and is not yet intended for for use outside
+// of WebRtc/Libjingle.
 class AudioMixer : public rtc::RefCountInterface {
  public:
   // A callback class that all mixer participants must inherit from/implement.
@@ -25,10 +28,11 @@
    public:
     enum class AudioFrameInfo {
       kNormal,  // The samples in audio_frame are valid and should be used.
-      kMuted,   // The samples in audio_frame should not be used, but should be
-      // implicitly interpreted as zero. Other fields in audio_frame
-      // may be read and should contain meaningful values.
-      kError  // audio_frame will not be used.
+      kMuted,   // The samples in audio_frame should not be used, but
+                // should be implicitly interpreted as zero. Other
+                // fields in audio_frame may be read and should
+                // contain meaningful values.
+      kError,   // The audio_frame will not be used.
     };
 
     struct AudioFrameWithInfo {
@@ -47,8 +51,8 @@
     // mixer.
     virtual AudioFrameWithInfo GetAudioFrameWithInfo(int sample_rate_hz) = 0;
 
-    // A way for a mixer implementation do distinguish participants.
-    virtual int ssrc() = 0;
+    // A way for a mixer implementation to distinguish participants.
+    virtual int Ssrc() = 0;
 
    protected:
     virtual ~Source() {}
@@ -75,4 +79,4 @@
 };
 }  // namespace webrtc
 
-#endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_
+#endif  // WEBRTC_API_AUDIO_AUDIO_MIXER_H_
diff --git a/webrtc/modules/BUILD.gn b/webrtc/modules/BUILD.gn
index d983360..6c472a3 100644
--- a/webrtc/modules/BUILD.gn
+++ b/webrtc/modules/BUILD.gn
@@ -19,7 +19,7 @@
     "audio_coding",
     "audio_conference_mixer",
     "audio_device",
-    "audio_mixer",
+    "audio_mixer:audio_mixer_impl",
     "audio_processing",
     "bitrate_controller",
     "desktop_capture",
@@ -629,6 +629,7 @@
       "../system_wrappers:system_wrappers",
       "../test:rtp_test_utils",
       "../test:test_common",
+      "../test:test_support",
       "../test:test_support_main",
       "../test:video_test_common",
       "audio_coding",
@@ -645,7 +646,8 @@
       "audio_coding:webrtc_opus",
       "audio_conference_mixer",
       "audio_device",
-      "audio_mixer",
+      "audio_mixer:audio_frame_manipulator",
+      "audio_mixer:audio_mixer_impl",
       "audio_processing",
       "audio_processing:audioproc_test_utils",
       "bitrate_controller",
diff --git a/webrtc/modules/audio_mixer/BUILD.gn b/webrtc/modules/audio_mixer/BUILD.gn
index 412b4d0..26adcf8 100644
--- a/webrtc/modules/audio_mixer/BUILD.gn
+++ b/webrtc/modules/audio_mixer/BUILD.gn
@@ -8,15 +8,12 @@
 
 import("../../build/webrtc.gni")
 
-config("audio_conference_mixer_config") {
-  include_dirs = [ "../../modules/include" ]
-}
-
-rtc_static_library("audio_mixer") {
+rtc_static_library("audio_mixer_impl") {
+  visibility = [
+    "../../audio:audio",
+    "../../modules/*",
+  ]
   sources = [
-    "audio_frame_manipulator.cc",
-    "audio_frame_manipulator.h",
-    "audio_mixer.h",
     "audio_mixer_impl.cc",
     "audio_mixer_impl.h",
     "audio_source_with_mix_status.cc",
@@ -24,17 +21,36 @@
   ]
 
   public = [
-    "audio_mixer.h",
+    "audio_mixer_impl.h",
   ]
 
-  public_configs = [ ":audio_conference_mixer_config" ]
+  public_deps = [
+    "../../api:audio_mixer_api",
+  ]
 
   deps = [
+    ":audio_frame_manipulator",
     "../..:webrtc_common",
     "../../base:rtc_base_approved",
     "../../modules/audio_processing",
     "../../modules/utility",
     "../../system_wrappers",
-    "../../voice_engine:level_indicator",
+  ]
+}
+
+rtc_static_library("audio_frame_manipulator") {
+  visibility = [
+    ":*",
+    "../../modules:*",
+  ]
+
+  sources = [
+    "audio_frame_manipulator.cc",
+    "audio_frame_manipulator.h",
+  ]
+
+  deps = [
+    "../../base:rtc_base_approved",
+    "../../modules/utility",
   ]
 }
diff --git a/webrtc/modules/audio_mixer/audio_frame_manipulator.cc b/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
index 426c21b..fca9a78 100644
--- a/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
+++ b/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
@@ -12,7 +12,6 @@
 #include "webrtc/modules/audio_mixer/audio_frame_manipulator.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/utility/include/audio_frame_operations.h"
-#include "webrtc/typedefs.h"
 
 namespace webrtc {
 
diff --git a/webrtc/modules/audio_mixer/audio_frame_manipulator.h b/webrtc/modules/audio_mixer/audio_frame_manipulator.h
index b149bf9..20b66ca 100644
--- a/webrtc/modules/audio_mixer/audio_frame_manipulator.h
+++ b/webrtc/modules/audio_mixer/audio_frame_manipulator.h
@@ -12,7 +12,6 @@
 #define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
 
 #include "webrtc/modules/include/module_common_types.h"
-#include "webrtc/typedefs.h"
 
 namespace webrtc {
 
diff --git a/webrtc/modules/audio_mixer/audio_mixer.gypi b/webrtc/modules/audio_mixer/audio_mixer.gypi
index 1ec0a4d..ee40a9c 100644
--- a/webrtc/modules/audio_mixer/audio_mixer.gypi
+++ b/webrtc/modules/audio_mixer/audio_mixer.gypi
@@ -9,24 +9,34 @@
 {
   'targets': [
     {
-      'target_name': 'audio_mixer',
+      'target_name': 'audio_mixer_impl',
       'type': 'static_library',
       'dependencies': [
+        'audio_frame_manipulator',
         'audio_processing',
         'webrtc_utility',
-        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
+        '<(webrtc_root)/api/api.gyp:audio_mixer_api',
         '<(webrtc_root)/base/base.gyp:rtc_base_approved',
-        '<(webrtc_root)/voice_engine/voice_engine.gyp:level_indicator',
+        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
       ],
       'sources': [
-        'audio_frame_manipulator.cc',
-        'audio_frame_manipulator.h',
-        'audio_mixer.h',
         'audio_mixer_impl.cc',
         'audio_mixer_impl.h',
         'audio_source_with_mix_status.cc',
         'audio_source_with_mix_status.h',
       ],
     },
+    {
+      'target_name': 'audio_frame_manipulator',
+      'type': 'static_library',
+      'dependencies': [
+          'webrtc_utility',
+          '<(webrtc_root)/base/base.gyp:rtc_base_approved',
+      ],
+      'sources': [
+        'audio_frame_manipulator.cc',
+        'audio_frame_manipulator.h',
+      ],
+    },
   ], # targets
 }
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index 87541ee..500bb78 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -14,14 +14,13 @@
 #include <memory>
 #include <vector>
 
+#include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/base/thread_checker.h"
-#include "webrtc/modules/audio_mixer/audio_mixer.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/system_wrappers/include/critical_section_wrapper.h"
-#include "webrtc/voice_engine/level_indicator.h"
 #include "webrtc/voice_engine_configurations.h"
 
 namespace webrtc {
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl_unittest.cc b/webrtc/modules/audio_mixer/audio_mixer_impl_unittest.cc
index 1e5f1fe..9147a15 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl_unittest.cc
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl_unittest.cc
@@ -14,10 +14,10 @@
 #include <memory>
 #include <utility>
 
+#include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/base/bind.h"
 #include "webrtc/base/thread.h"
 #include "webrtc/modules/audio_mixer/audio_mixer_impl.h"
-#include "webrtc/modules/audio_mixer/audio_mixer.h"
 #include "webrtc/test/gmock.h"
 
 using testing::_;
@@ -60,7 +60,7 @@
 
   MOCK_METHOD1(GetAudioFrameWithInfo, AudioFrameWithInfo(int sample_rate_hz));
 
-  MOCK_METHOD0(ssrc, int());
+  MOCK_METHOD0(Ssrc, int());
 
   AudioFrame* fake_frame() { return &fake_frame_; }
   AudioFrameInfo fake_info() { return fake_audio_frame_info_; }
diff --git a/webrtc/modules/audio_mixer/audio_source_with_mix_status.h b/webrtc/modules/audio_mixer/audio_source_with_mix_status.h
index 167118f..4849d61 100644
--- a/webrtc/modules/audio_mixer/audio_source_with_mix_status.h
+++ b/webrtc/modules/audio_mixer/audio_source_with_mix_status.h
@@ -11,7 +11,7 @@
 #ifndef WEBRTC_MODULES_AUDIO_MIXER_AUDIO_SOURCE_WITH_MIX_STATUS_H_
 #define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_SOURCE_WITH_MIX_STATUS_H_
 
-#include "webrtc/modules/audio_mixer/audio_mixer.h"
+#include "webrtc/api/audio/audio_mixer.h"
 
 namespace webrtc {