New VideoDecoderFactoryTemplate.

The VideoDecoderFactoryTemplate takes decoder implementations as template arguments, making it possible to easily implement a VideoDecoderFactory only using the implementations required for the particular application. This will replace the BuiltinVideoDecoderFactory.

Bug: webrtc:13573
Change-Id: I0213acd20b69dacf06fc6934851b73bd19b1afc8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/268470
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37523}

api/video_codecs/video_decoder_factory_template.h

@@ -0,0 +1,95 @@
+/*
+ *  Copyright (c) 2022 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 API_VIDEO_CODECS_VIDEO_DECODER_FACTORY_TEMPLATE_H_
+#define API_VIDEO_CODECS_VIDEO_DECODER_FACTORY_TEMPLATE_H_
+
+#include <memory>
+#include <vector>
+
+#include "absl/algorithm/container.h"
+#include "api/array_view.h"
+#include "api/video_codecs/video_decoder.h"
+#include "api/video_codecs/video_decoder_factory.h"
+
+namespace webrtc {
+// The VideoDecoderFactoryTemplate supports decoder implementations given as
+// template arguments.
+//
+// To include a decoder in the factory it requires two static members
+// functions to be defined:
+//
+//   // Returns the supported SdpVideoFormats this decoder can decode.
+//   static std::vector<SdpVideoFormat> SupportedFormats();
+//
+//   // Creates a decoder instance for the given format.
+//   static std::unique_ptr<VideoDecoder>
+//       CreateDecoder(const SdpVideoFormat& format);
+//
+// Note that the order of the template arguments matter as the factory will
+// return the first decoder implementation supporting the given SdpVideoFormat.
+template <typename... Ts>
+class VideoDecoderFactoryTemplate : public VideoDecoderFactory {
+ public:
+  std::vector<SdpVideoFormat> GetSupportedFormats() const override {
+    return GetSupportedFormatsInternal<Ts...>();
+  }
+
+  std::unique_ptr<VideoDecoder> CreateVideoDecoder(
+      const SdpVideoFormat& format) override {
+    return CreateVideoDecoderInternal<Ts...>(format);
+  }
+
+ private:
+  bool IsFormatInList(
+      const SdpVideoFormat& format,
+      rtc::ArrayView<const SdpVideoFormat> supported_formats) const {
+    return absl::c_any_of(
+        supported_formats, [&](const SdpVideoFormat& supported_format) {
+          return supported_format.name == format.name &&
+                 supported_format.parameters == format.parameters;
+        });
+  }
+
+  template <typename V, typename... Vs>
+  std::vector<SdpVideoFormat> GetSupportedFormatsInternal() const {
+    auto supported_formats = V::SupportedFormats();
+
+    if constexpr (sizeof...(Vs) > 0) {
+      // Supported formats may overlap between implementations, so duplicates
+      // should be filtered out.
+      for (const auto& other_format : GetSupportedFormatsInternal<Vs...>()) {
+        if (!IsFormatInList(other_format, supported_formats)) {
+          supported_formats.push_back(other_format);
+        }
+      }
+    }
+
+    return supported_formats;
+  }
+
+  template <typename V, typename... Vs>
+  std::unique_ptr<VideoDecoder> CreateVideoDecoderInternal(
+      const SdpVideoFormat& format) {
+    if (IsFormatInList(format, V::SupportedFormats())) {
+      return V::CreateDecoder(format);
+    }
+
+    if constexpr (sizeof...(Vs) > 0) {
+      return CreateVideoDecoderInternal<Vs...>(format);
+    }
+
+    return nullptr;
+  }
+};
+
+}  // namespace webrtc
+
+#endif  // API_VIDEO_CODECS_VIDEO_DECODER_FACTORY_TEMPLATE_H_