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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_ENCODER_FACTORY_TEMPLATE_H_
#define API_AUDIO_CODECS_AUDIO_ENCODER_FACTORY_TEMPLATE_H_
#include <memory>
#include <vector>
#include "api/audio_codecs/audio_encoder_factory.h"
#include "api/scoped_refptr.h"
#include "rtc_base/ref_counted_object.h"
namespace webrtc {
namespace audio_encoder_factory_template_impl {
template <typename... Ts>
struct Helper;
// Base case: 0 template parameters.
template <>
struct Helper<> {
static void AppendSupportedEncoders(std::vector<AudioCodecSpec>* specs) {}
static absl::optional<AudioCodecInfo> QueryAudioEncoder(
const SdpAudioFormat& format) {
return absl::nullopt;
}
static std::unique_ptr<AudioEncoder> MakeAudioEncoder(
int payload_type,
const SdpAudioFormat& format,
absl::optional<AudioCodecPairId> codec_pair_id) {
return nullptr;
}
};
// 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 AppendSupportedEncoders(std::vector<AudioCodecSpec>* specs) {
T::AppendSupportedEncoders(specs);
Helper<Ts...>::AppendSupportedEncoders(specs);
}
static absl::optional<AudioCodecInfo> QueryAudioEncoder(
const SdpAudioFormat& format) {
auto opt_config = T::SdpToConfig(format);
static_assert(std::is_same<decltype(opt_config),
absl::optional<typename T::Config>>::value,
"T::SdpToConfig() must return a value of type "
"absl::optional<T::Config>");
return opt_config ? absl::optional<AudioCodecInfo>(
T::QueryAudioEncoder(*opt_config))
: Helper<Ts...>::QueryAudioEncoder(format);
}
static std::unique_ptr<AudioEncoder> MakeAudioEncoder(
int payload_type,
const SdpAudioFormat& format,
absl::optional<AudioCodecPairId> codec_pair_id) {
auto opt_config = T::SdpToConfig(format);
if (opt_config) {
return T::MakeAudioEncoder(*opt_config, payload_type, codec_pair_id);
} else {
return Helper<Ts...>::MakeAudioEncoder(payload_type, format,
codec_pair_id);
}
}
};
template <typename... Ts>
class AudioEncoderFactoryT : public AudioEncoderFactory {
public:
std::vector<AudioCodecSpec> GetSupportedEncoders() override {
std::vector<AudioCodecSpec> specs;
Helper<Ts...>::AppendSupportedEncoders(&specs);
return specs;
}
absl::optional<AudioCodecInfo> QueryAudioEncoder(
const SdpAudioFormat& format) override {
return Helper<Ts...>::QueryAudioEncoder(format);
}
std::unique_ptr<AudioEncoder> MakeAudioEncoder(
int payload_type,
const SdpAudioFormat& format,
absl::optional<AudioCodecPairId> codec_pair_id) override {
return Helper<Ts...>::MakeAudioEncoder(payload_type, format, codec_pair_id);
}
};
} // namespace audio_encoder_factory_template_impl
// Make an AudioEncoderFactory that can create instances of the given encoders.
//
// Each encoder 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 an encoder of our
// // type.
// absl::optional<ConfigType> SdpToConfig(const SdpAudioFormat& audio_format);
//
// // Appends zero or more AudioCodecSpecs to the list that will be returned
// // by AudioEncoderFactory::GetSupportedEncoders().
// void AppendSupportedEncoders(std::vector<AudioCodecSpec>* specs);
//
// // Returns information about how this format would be encoded. Used to
// // implement AudioEncoderFactory::QueryAudioEncoder().
// AudioCodecInfo QueryAudioEncoder(const ConfigType& config);
//
// // Creates an AudioEncoder for the specified format. Used to implement
// // AudioEncoderFactory::MakeAudioEncoder().
// std::unique_ptr<AudioDecoder> MakeAudioEncoder(
// const ConfigType& config,
// int payload_type,
// absl::optional<AudioCodecPairId> codec_pair_id);
//
// ConfigType should be a type that encapsulates all the settings needed to
// create an AudioEncoder. T::Config (where T is the encoder 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
// encoders 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 CreateBuiltinAudioEncoderFactory() for an example of
// how it is used.
template <typename... Ts>
rtc::scoped_refptr<AudioEncoderFactory> CreateAudioEncoderFactory() {
// There's no technical reason we couldn't allow zero template parameters,
// but such a factory couldn't create any encoders, 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 rtc::make_ref_counted<
audio_encoder_factory_template_impl::AudioEncoderFactoryT<Ts...>>();
}
} // namespace webrtc
#endif // API_AUDIO_CODECS_AUDIO_ENCODER_FACTORY_TEMPLATE_H_
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