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/*
* Copyright (c) 2017 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_AUDIO_CODECS_AUDIO_DECODER_FACTORY_TEMPLATE_H_
#define API_AUDIO_CODECS_AUDIO_DECODER_FACTORY_TEMPLATE_H_
#include <memory>
#include <optional>
#include <type_traits>
#include <utility>
#include <vector>
#include "absl/base/nullability.h"
#include "api/audio_codecs/audio_codec_pair_id.h"
#include "api/audio_codecs/audio_decoder.h"
#include "api/audio_codecs/audio_decoder_factory.h"
#include "api/audio_codecs/audio_format.h"
#include "api/environment/environment.h"
#include "api/make_ref_counted.h"
#include "api/scoped_refptr.h"
namespace webrtc {
namespace audio_decoder_factory_template_impl {
template <typename... Ts>
struct Helper;
// Base case: 0 template parameters.
template <>
struct Helper<> {
static void AppendSupportedDecoders(
std::vector<AudioCodecSpec>* /* specs */) {}
static bool IsSupportedDecoder(const SdpAudioFormat& /* format */) {
return false;
}
static absl_nullable std::unique_ptr<AudioDecoder> MakeAudioDecoder(
const Environment& /* env */,
const SdpAudioFormat& /* format */,
std::optional<AudioCodecPairId> /* codec_pair_id */) {
return nullptr;
}
};
// Use ranked overloads (abseil.io/tips/229) for dispatching.
struct Rank0 {};
struct Rank1 : Rank0 {};
template <typename Trait,
typename = std::enable_if_t<std::is_convertible_v<
decltype(Trait::MakeAudioDecoder(
std::declval<Environment>(),
std::declval<typename Trait::Config>(),
std::declval<std::optional<AudioCodecPairId>>())),
std::unique_ptr<AudioDecoder>>>>
absl_nullable std::unique_ptr<AudioDecoder> CreateDecoder(
Rank1,
const Environment& env,
const typename Trait::Config& config,
std::optional<AudioCodecPairId> codec_pair_id) {
return Trait::MakeAudioDecoder(env, config, codec_pair_id);
}
template <typename Trait,
typename = std::enable_if_t<std::is_convertible_v<
decltype(Trait::MakeAudioDecoder(
std::declval<typename Trait::Config>(),
std::declval<std::optional<AudioCodecPairId>>())),
std::unique_ptr<AudioDecoder>>>>
absl_nullable std::unique_ptr<AudioDecoder> CreateDecoder(
Rank0,
const Environment& /* env */,
const typename Trait::Config& config,
std::optional<AudioCodecPairId> codec_pair_id) {
return Trait::MakeAudioDecoder(config, codec_pair_id);
}
// Inductive case: Called with n + 1 template parameters; calls subroutines
// with n template parameters.
template <typename T, typename... Ts>
struct Helper<T, Ts...> {
static void AppendSupportedDecoders(std::vector<AudioCodecSpec>* specs) {
T::AppendSupportedDecoders(specs);
Helper<Ts...>::AppendSupportedDecoders(specs);
}
static bool IsSupportedDecoder(const SdpAudioFormat& format) {
auto opt_config = T::SdpToConfig(format);
static_assert(std::is_same<decltype(opt_config),
std::optional<typename T::Config>>::value,
"T::SdpToConfig() must return a value of type "
"std::optional<T::Config>");
return opt_config ? true : Helper<Ts...>::IsSupportedDecoder(format);
}
static absl_nullable std::unique_ptr<AudioDecoder> MakeAudioDecoder(
const Environment& env,
const SdpAudioFormat& format,
std::optional<AudioCodecPairId> codec_pair_id) {
auto opt_config = T::SdpToConfig(format);
return opt_config.has_value()
? CreateDecoder<T>(Rank1{}, env, *opt_config, codec_pair_id)
: Helper<Ts...>::MakeAudioDecoder(env, format, codec_pair_id);
}
};
template <typename... Ts>
class AudioDecoderFactoryT : public AudioDecoderFactory {
public:
std::vector<AudioCodecSpec> GetSupportedDecoders() override {
std::vector<AudioCodecSpec> specs;
Helper<Ts...>::AppendSupportedDecoders(&specs);
return specs;
}
bool IsSupportedDecoder(const SdpAudioFormat& format) override {
return Helper<Ts...>::IsSupportedDecoder(format);
}
absl_nullable std::unique_ptr<AudioDecoder> Create(
const Environment& env,
const SdpAudioFormat& format,
std::optional<AudioCodecPairId> codec_pair_id) override {
return Helper<Ts...>::MakeAudioDecoder(env, format, codec_pair_id);
}
};
} // namespace audio_decoder_factory_template_impl
// Make an AudioDecoderFactory that can create instances of the given decoders.
//
// Each decoder type is given as a template argument to the function; it should
// be a struct with the following static member functions:
//
// // Converts `audio_format` to a ConfigType instance. Returns an empty
// // optional if `audio_format` doesn't correctly specify a decoder of our
// // type.
// std::optional<ConfigType> SdpToConfig(const SdpAudioFormat& audio_format);
//
// // Appends zero or more AudioCodecSpecs to the list that will be returned
// // by AudioDecoderFactory::GetSupportedDecoders().
// void AppendSupportedDecoders(std::vector<AudioCodecSpec>* specs);
//
// // Creates an AudioDecoder for the specified format. Used to implement
// // AudioDecoderFactory::Create().
// std::unique_ptr<AudioEncoder> MakeAudioDecoder(
// const Environment& env,
// const ConfigType& config,
// std::optional<AudioCodecPairId> codec_pair_id);
// or
// std::unique_ptr<AudioDecoder> MakeAudioDecoder(
// const ConfigType& config,
// std::optional<AudioCodecPairId> codec_pair_id);
//
// ConfigType should be a type that encapsulates all the settings needed to
// create an AudioDecoder. T::Config (where T is the decoder struct) should
// either be the config type, or an alias for it.
//
// Whenever it tries to do something, the new factory will try each of the
// decoder types in the order they were specified in the template argument
// list, stopping at the first one that claims to be able to do the job.
//
// TODO(kwiberg): Point at CreateBuiltinAudioDecoderFactory() for an example of
// how it is used.
template <typename... Ts>
scoped_refptr<AudioDecoderFactory> CreateAudioDecoderFactory() {
// There's no technical reason we couldn't allow zero template parameters,
// but such a factory couldn't create any decoders, and callers can do this
// by mistake by simply forgetting the <> altogether. So we forbid it in
// order to prevent caller foot-shooting.
static_assert(sizeof...(Ts) >= 1,
"Caller must give at least one template parameter");
return make_ref_counted<
audio_decoder_factory_template_impl::AudioDecoderFactoryT<Ts...>>();
}
} // namespace webrtc
#endif // API_AUDIO_CODECS_AUDIO_DECODER_FACTORY_TEMPLATE_H_
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