Move VideoDecoder::Create() logic to separate internal video decoder factory

The goal with this CL is to move implementation details out from the
webrtc root (webrtc/video_decoder.h) to simplify the dependency graph.
Another goal is to streamline the creation of VideoDecoders in
webrtcvideoengine2.cc; it will now have two factories of the same
WebRtcVideoDecoderFactory type, one internal and one external.

Specifically, this CL:
 * Removes webrtc::VideoDecoder::DecoderType and use webrtc::VideoCodecType
   instead.
 * Removes 'static VideoDecoder* Create(DecoderType codec_type)' and
   moves the create function to the internal decoder factory instead.
 * Removes video_decoder.cc. webrtc::VideoDecoder is now just an
   interface without any static functions.

BUG=webrtc:6743

Review-Url: https://codereview.webrtc.org/2521203002
Cr-Commit-Position: refs/heads/master@{#15350}
diff --git a/webrtc/media/BUILD.gn b/webrtc/media/BUILD.gn
index 93f98a9..f88ff49 100644
--- a/webrtc/media/BUILD.gn
+++ b/webrtc/media/BUILD.gn
@@ -136,6 +136,8 @@
     "base/videocommon.h",
     "base/videoframe.h",
     "base/videosourcebase.h",
+    "engine/internaldecoderfactory.cc",
+    "engine/internaldecoderfactory.h",
     "engine/internalencoderfactory.cc",
     "engine/internalencoderfactory.h",
     "engine/nullwebrtcvideoengine.h",
@@ -348,6 +350,7 @@
       "base/videocapturer_unittest.cc",
       "base/videocommon_unittest.cc",
       "base/videoengine_unittest.h",
+      "engine/internaldecoderfactory_unittest.cc",
       "engine/nullwebrtcvideoengine_unittest.cc",
       "engine/payload_type_mapper_unittest.cc",
       "engine/simulcast_unittest.cc",
diff --git a/webrtc/media/engine/internaldecoderfactory.cc b/webrtc/media/engine/internaldecoderfactory.cc
new file mode 100644
index 0000000..760575d
--- /dev/null
+++ b/webrtc/media/engine/internaldecoderfactory.cc
@@ -0,0 +1,90 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/media/engine/internaldecoderfactory.h"
+
+#include <utility>
+
+#include "webrtc/base/logging.h"
+#include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
+#include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"
+#include "webrtc/modules/video_coding/codecs/vp9/include/vp9.h"
+
+namespace cricket {
+
+namespace {
+
+// Video decoder class to be used for unknown codecs. Doesn't support decoding
+// but logs messages to LS_ERROR.
+class NullVideoDecoder : public webrtc::VideoDecoder {
+ public:
+  int32_t InitDecode(const webrtc::VideoCodec* codec_settings,
+                     int32_t number_of_cores) override {
+    LOG(LS_ERROR) << "Can't initialize NullVideoDecoder.";
+    return WEBRTC_VIDEO_CODEC_OK;
+  }
+
+  int32_t Decode(const webrtc::EncodedImage& input_image,
+                 bool missing_frames,
+                 const webrtc::RTPFragmentationHeader* fragmentation,
+                 const webrtc::CodecSpecificInfo* codec_specific_info,
+                 int64_t render_time_ms) override {
+    LOG(LS_ERROR) << "The NullVideoDecoder doesn't support decoding.";
+    return WEBRTC_VIDEO_CODEC_OK;
+  }
+
+  int32_t RegisterDecodeCompleteCallback(
+      webrtc::DecodedImageCallback* callback) override {
+    LOG(LS_ERROR)
+        << "Can't register decode complete callback on NullVideoDecoder.";
+    return WEBRTC_VIDEO_CODEC_OK;
+  }
+
+  int32_t Release() override { return WEBRTC_VIDEO_CODEC_OK; }
+
+  const char* ImplementationName() const override { return "NullVideoDecoder"; }
+};
+
+}  // anonymous namespace
+
+InternalDecoderFactory::InternalDecoderFactory() {}
+
+InternalDecoderFactory::~InternalDecoderFactory() {}
+
+// WebRtcVideoDecoderFactory implementation.
+webrtc::VideoDecoder* InternalDecoderFactory::CreateVideoDecoder(
+    webrtc::VideoCodecType type) {
+  switch (type) {
+    case webrtc::kVideoCodecH264:
+      if (webrtc::H264Decoder::IsSupported())
+        return webrtc::H264Decoder::Create();
+      // This could happen in a software-fallback for a codec type only
+      // supported externally (e.g. H.264 on iOS or Android) or in current usage
+      // in WebRtcVideoEngine2 if the external decoder fails to be created.
+      LOG(LS_ERROR) << "Unable to create an H.264 decoder fallback. "
+                    << "Decoding of this stream will be broken.";
+      return new NullVideoDecoder();
+    case webrtc::kVideoCodecVP8:
+      return webrtc::VP8Decoder::Create();
+    case webrtc::kVideoCodecVP9:
+      RTC_DCHECK(webrtc::VP9Decoder::IsSupported());
+      return webrtc::VP9Decoder::Create();
+    default:
+      LOG(LS_ERROR) << "Creating NullVideoDecoder for unsupported codec.";
+      return new NullVideoDecoder();
+  }
+}
+
+void InternalDecoderFactory::DestroyVideoDecoder(
+    webrtc::VideoDecoder* decoder) {
+  delete decoder;
+}
+
+}  // namespace cricket
diff --git a/webrtc/media/engine/internaldecoderfactory.h b/webrtc/media/engine/internaldecoderfactory.h
new file mode 100644
index 0000000..20ceecc
--- /dev/null
+++ b/webrtc/media/engine/internaldecoderfactory.h
@@ -0,0 +1,34 @@
+/*
+ *  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_MEDIA_ENGINE_INTERNALDECODERFACTORY_H_
+#define WEBRTC_MEDIA_ENGINE_INTERNALDECODERFACTORY_H_
+
+#include <vector>
+
+#include "webrtc/media/engine/webrtcvideodecoderfactory.h"
+
+namespace cricket {
+
+class InternalDecoderFactory : public WebRtcVideoDecoderFactory {
+ public:
+  InternalDecoderFactory();
+  virtual ~InternalDecoderFactory();
+
+  // WebRtcVideoDecoderFactory implementation.
+  webrtc::VideoDecoder* CreateVideoDecoder(
+      webrtc::VideoCodecType type) override;
+
+  void DestroyVideoDecoder(webrtc::VideoDecoder* decoder) override;
+};
+
+}  // namespace cricket
+
+#endif  // WEBRTC_MEDIA_ENGINE_INTERNALDECODERFACTORY_H_
diff --git a/webrtc/media/engine/internaldecoderfactory_unittest.cc b/webrtc/media/engine/internaldecoderfactory_unittest.cc
new file mode 100644
index 0000000..bf1ca50
--- /dev/null
+++ b/webrtc/media/engine/internaldecoderfactory_unittest.cc
@@ -0,0 +1,21 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/media/engine/internaldecoderfactory.h"
+
+#include "webrtc/test/gtest.h"
+
+TEST(InternalDecoderFactory, TestVP8) {
+  cricket::InternalDecoderFactory factory;
+  webrtc::VideoDecoder* decoder =
+      factory.CreateVideoDecoder(webrtc::kVideoCodecVP8);
+  EXPECT_TRUE(decoder);
+  factory.DestroyVideoDecoder(decoder);
+}
diff --git a/webrtc/media/engine/videodecodersoftwarefallbackwrapper.cc b/webrtc/media/engine/videodecodersoftwarefallbackwrapper.cc
index 8dd0f84..cd6eef9 100644
--- a/webrtc/media/engine/videodecodersoftwarefallbackwrapper.cc
+++ b/webrtc/media/engine/videodecodersoftwarefallbackwrapper.cc
@@ -13,34 +13,15 @@
 #include <string>
 
 #include "webrtc/base/logging.h"
+#include "webrtc/media/engine/internaldecoderfactory.h"
 #include "webrtc/modules/video_coding/include/video_error_codes.h"
 
 namespace webrtc {
 
-namespace {
-
-VideoDecoder::DecoderType CodecTypeToDecoderType(VideoCodecType codec_type) {
-  switch (codec_type) {
-    case kVideoCodecH264:
-      return VideoDecoder::kH264;
-    case kVideoCodecVP8:
-      return VideoDecoder::kVp8;
-    case kVideoCodecVP9:
-      return VideoDecoder::kVp9;
-    default:
-      return VideoDecoder::kUnsupportedCodec;
-  }
-}
-
-}  // anonymous namespace
-
 VideoDecoderSoftwareFallbackWrapper::VideoDecoderSoftwareFallbackWrapper(
     VideoCodecType codec_type,
     VideoDecoder* decoder)
-    : decoder_type_(CodecTypeToDecoderType(codec_type)),
-      decoder_(decoder),
-      callback_(nullptr) {
-}
+    : codec_type_(codec_type), decoder_(decoder), callback_(nullptr) {}
 
 int32_t VideoDecoderSoftwareFallbackWrapper::InitDecode(
     const VideoCodec* codec_settings,
@@ -51,10 +32,12 @@
 }
 
 bool VideoDecoderSoftwareFallbackWrapper::InitFallbackDecoder() {
-  RTC_CHECK(decoder_type_ != kUnsupportedCodec)
+  RTC_CHECK(codec_type_ != kVideoCodecUnknown)
       << "Decoder requesting fallback to codec not supported in software.";
   LOG(LS_WARNING) << "Decoder falling back to software decoding.";
-  fallback_decoder_.reset(VideoDecoder::Create(decoder_type_));
+  cricket::InternalDecoderFactory internal_decoder_factory;
+  fallback_decoder_.reset(
+      internal_decoder_factory.CreateVideoDecoder(codec_type_));
   if (fallback_decoder_->InitDecode(&codec_settings_, number_of_cores_) !=
       WEBRTC_VIDEO_CODEC_OK) {
     LOG(LS_ERROR) << "Failed to initialize software-decoder fallback.";
diff --git a/webrtc/media/engine/videodecodersoftwarefallbackwrapper.h b/webrtc/media/engine/videodecodersoftwarefallbackwrapper.h
index 8e1a97d..93c9278 100644
--- a/webrtc/media/engine/videodecodersoftwarefallbackwrapper.h
+++ b/webrtc/media/engine/videodecodersoftwarefallbackwrapper.h
@@ -46,7 +46,7 @@
  private:
   bool InitFallbackDecoder();
 
-  const DecoderType decoder_type_;
+  const VideoCodecType codec_type_;
   VideoDecoder* const decoder_;
 
   VideoCodec codec_settings_;
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index fc91ca6..9396fcc 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -25,6 +25,7 @@
 #include "webrtc/common_video/h264/profile_level_id.h"
 #include "webrtc/media/engine/constants.h"
 #include "webrtc/media/engine/internalencoderfactory.h"
+#include "webrtc/media/engine/internaldecoderfactory.h"
 #include "webrtc/media/engine/simulcast.h"
 #include "webrtc/media/engine/videoencodersoftwarefallbackwrapper.h"
 #include "webrtc/media/engine/videodecodersoftwarefallbackwrapper.h"
@@ -2225,28 +2226,14 @@
         external_decoder_factory_->CreateVideoDecoderWithParams(
             type, {stream_params_.id});
     if (decoder != NULL) {
-      return AllocatedDecoder(decoder, type, true);
+      return AllocatedDecoder(decoder, type, true /* is_external */);
     }
   }
 
-  if (type == webrtc::kVideoCodecVP8) {
-    return AllocatedDecoder(
-        webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kVp8), type, false);
-  }
-
-  if (type == webrtc::kVideoCodecVP9) {
-    return AllocatedDecoder(
-        webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kVp9), type, false);
-  }
-
-  if (type == webrtc::kVideoCodecH264) {
-    return AllocatedDecoder(
-        webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kH264), type, false);
-  }
-
-  return AllocatedDecoder(
-      webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kUnsupportedCodec),
-      webrtc::kVideoCodecUnknown, false);
+  InternalDecoderFactory internal_decoder_factory;
+  return AllocatedDecoder(internal_decoder_factory.CreateVideoDecoderWithParams(
+                              type, {stream_params_.id}),
+                          type, false /* is_external */);
 }
 
 void WebRtcVideoChannel2::WebRtcVideoReceiveStream::ConfigureCodecs(
diff --git a/webrtc/test/encoder_settings.cc b/webrtc/test/encoder_settings.cc
index 80c42ef..061fafc 100644
--- a/webrtc/test/encoder_settings.cc
+++ b/webrtc/test/encoder_settings.cc
@@ -12,8 +12,10 @@
 #include <algorithm>
 #include <string>
 
+#include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
+#include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"
+#include "webrtc/modules/video_coding/codecs/vp9/include/vp9.h"
 #include "webrtc/test/fake_decoder.h"
-#include "webrtc/video_decoder.h"
 
 namespace webrtc {
 namespace test {
@@ -85,11 +87,11 @@
   decoder.payload_type = encoder_settings.payload_type;
   decoder.payload_name = encoder_settings.payload_name;
   if (encoder_settings.payload_name == "H264") {
-    decoder.decoder = VideoDecoder::Create(VideoDecoder::kH264);
+    decoder.decoder = H264Decoder::Create();
   } else if (encoder_settings.payload_name == "VP8") {
-    decoder.decoder = VideoDecoder::Create(VideoDecoder::kVp8);
+    decoder.decoder = VP8Decoder::Create();
   } else if (encoder_settings.payload_name == "VP9") {
-    decoder.decoder = VideoDecoder::Create(VideoDecoder::kVp9);
+    decoder.decoder = VP9Decoder::Create();
   } else {
     decoder.decoder = new FakeDecoder();
   }
diff --git a/webrtc/video/BUILD.gn b/webrtc/video/BUILD.gn
index 8a99fbf..66191ef 100644
--- a/webrtc/video/BUILD.gn
+++ b/webrtc/video/BUILD.gn
@@ -36,7 +36,6 @@
     "stream_synchronization.h",
     "transport_adapter.cc",
     "transport_adapter.h",
-    "video_decoder.cc",
     "video_receive_stream.cc",
     "video_receive_stream.h",
     "video_send_stream.cc",
diff --git a/webrtc/video/video_decoder.cc b/webrtc/video/video_decoder.cc
deleted file mode 100644
index 4ac4ff5..0000000
--- a/webrtc/video/video_decoder.cc
+++ /dev/null
@@ -1,78 +0,0 @@
-/*
- *  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/video_decoder.h"
-
-#include "webrtc/base/checks.h"
-#include "webrtc/base/logging.h"
-#include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
-#include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"
-#include "webrtc/modules/video_coding/codecs/vp9/include/vp9.h"
-
-namespace webrtc {
-VideoDecoder* VideoDecoder::Create(VideoDecoder::DecoderType codec_type) {
-  switch (codec_type) {
-    case kH264:
-      if (!H264Decoder::IsSupported()) {
-        // This could happen in a software-fallback for a codec type only
-        // supported externally (e.g. H.264 on iOS or Android) or in current
-        // usage in WebRtcVideoEngine2 if the external decoder fails to be
-        // created.
-        LOG(LS_ERROR) << "Unable to create an H.264 decoder fallback. "
-                      << "Decoding of this stream will be broken.";
-        return new NullVideoDecoder();
-      }
-      return H264Decoder::Create();
-    case kVp8:
-      return VP8Decoder::Create();
-    case kVp9:
-      RTC_DCHECK(VP9Decoder::IsSupported());
-      return VP9Decoder::Create();
-    case kUnsupportedCodec:
-      LOG(LS_ERROR) << "Creating NullVideoDecoder for unsupported codec.";
-      return new NullVideoDecoder();
-  }
-  RTC_NOTREACHED();
-  return nullptr;
-}
-
-NullVideoDecoder::NullVideoDecoder() {}
-
-int32_t NullVideoDecoder::InitDecode(const VideoCodec* codec_settings,
-                                     int32_t number_of_cores) {
-  LOG(LS_ERROR) << "Can't initialize NullVideoDecoder.";
-  return WEBRTC_VIDEO_CODEC_OK;
-}
-
-int32_t NullVideoDecoder::Decode(const EncodedImage& input_image,
-    bool missing_frames,
-    const RTPFragmentationHeader* fragmentation,
-    const CodecSpecificInfo* codec_specific_info,
-    int64_t render_time_ms) {
-  LOG(LS_ERROR) << "The NullVideoDecoder doesn't support decoding.";
-  return WEBRTC_VIDEO_CODEC_OK;
-}
-
-int32_t NullVideoDecoder::RegisterDecodeCompleteCallback(
-    DecodedImageCallback* callback) {
-  LOG(LS_ERROR)
-      << "Can't register decode complete callback on NullVideoDecoder.";
-  return WEBRTC_VIDEO_CODEC_OK;
-}
-
-int32_t NullVideoDecoder::Release() {
-  return WEBRTC_VIDEO_CODEC_OK;
-}
-
-const char* NullVideoDecoder::ImplementationName() const {
-  return "NullVideoDecoder";
-}
-
-}  // namespace webrtc
diff --git a/webrtc/video_decoder.h b/webrtc/video_decoder.h
index 8c89ce9..b8d2c96 100644
--- a/webrtc/video_decoder.h
+++ b/webrtc/video_decoder.h
@@ -50,15 +50,6 @@
 
 class VideoDecoder {
  public:
-  enum DecoderType {
-    kH264,
-    kVp8,
-    kVp9,
-    kUnsupportedCodec,
-  };
-
-  static VideoDecoder* Create(DecoderType codec_type);
-
   virtual ~VideoDecoder() {}
 
   virtual int32_t InitDecode(const VideoCodec* codec_settings,
@@ -83,29 +74,6 @@
   virtual const char* ImplementationName() const { return "unknown"; }
 };
 
-// Video decoder class to be used for unknown codecs. Doesn't support decoding
-// but logs messages to LS_ERROR.
-class NullVideoDecoder : public VideoDecoder {
- public:
-  NullVideoDecoder();
-
-  int32_t InitDecode(const VideoCodec* codec_settings,
-                     int32_t number_of_cores) override;
-
-  int32_t Decode(const EncodedImage& input_image,
-                 bool missing_frames,
-                 const RTPFragmentationHeader* fragmentation,
-                 const CodecSpecificInfo* codec_specific_info,
-                 int64_t render_time_ms) override;
-
-  int32_t RegisterDecodeCompleteCallback(
-      DecodedImageCallback* callback) override;
-
-  int32_t Release() override;
-
-  const char* ImplementationName() const override;
-};
-
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_DECODER_H_