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+/*
+ * 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_