video/config/video_encoder_config.h

/*
 *  Copyright (c) 2013 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 VIDEO_CONFIG_VIDEO_ENCODER_CONFIG_H_
#define VIDEO_CONFIG_VIDEO_ENCODER_CONFIG_H_

#include <stddef.h>

#include <optional>
#include <string>
#include <vector>

#include "api/field_trials_view.h"
#include "api/scoped_refptr.h"
#include "api/video/resolution.h"
#include "api/video_codecs/scalability_mode.h"
#include "api/video_codecs/sdp_video_format.h"
#include "api/video_codecs/video_codec.h"
#include "rtc_base/ref_count.h"

namespace webrtc {

// The `VideoStream` struct describes a simulcast layer, or "stream".
struct VideoStream {
  VideoStream();
  ~VideoStream();
  VideoStream(const VideoStream& other);
  std::string ToString() const;

  // Width/Height in pixels.
  // This is the actual width and height used to configure encoder,
  // which might be less than `scale_resolution_down_to` due to adaptation
  // or due to the source providing smaller frames than requested.
  size_t width;
  size_t height;

  // Frame rate in fps.
  int max_framerate;

  // Bitrate, in bps, for the stream.
  int min_bitrate_bps;
  int target_bitrate_bps;
  int max_bitrate_bps;

  // Scaling factor applied to the stream size.
  // `width` and `height` values are already scaled down.
  double scale_resolution_down_by;

  // Maximum Quantization Parameter to use when encoding the stream.
  int max_qp;

  // Determines the number of temporal layers that the stream should be
  // encoded with. This value should be greater than zero.
  // TODO(brandtr): This class is used both for configuring the encoder
  // (meaning that this field _must_ be set), and for signaling the app-level
  // encoder settings (meaning that the field _may_ be set). We should separate
  // this and remove this optional instead.
  std::optional<size_t> num_temporal_layers;

  // The priority of this stream, to be used when allocating resources
  // between multiple streams.
  std::optional<double> bitrate_priority;

  std::optional<ScalabilityMode> scalability_mode;

  // If this stream is enabled by the user, or not.
  bool active;

  // An optional user supplied max_frame_resolution
  // than can be set independently of (adapted) VideoSource.
  // This value is set from RtpEncodingParameters::scale_resolution_down_to
  // (i.e. used for signaling app-level settings).
  //
  // The actual encode resolution is in `width` and `height`,
  // which can be lower than scale_resolution_down_to,
  // e.g. if source only provides lower resolution or
  // if resource adaptation is active.
  std::optional<Resolution> scale_resolution_down_to;
};

class VideoEncoderConfig {
 public:
  // These are reference counted to permit copying VideoEncoderConfig and be
  // kept alive until all encoder_specific_settings go out of scope.
  // TODO(kthelgason): Consider removing the need for copying VideoEncoderConfig
  // and use std::optional for encoder_specific_settings instead.
  class EncoderSpecificSettings : public RefCountInterface {
   public:
    // TODO(pbos): Remove FillEncoderSpecificSettings as soon as VideoCodec is
    // not in use and encoder implementations ask for codec-specific structs
    // directly.
    void FillEncoderSpecificSettings(VideoCodec* codec_struct) const;

    virtual void FillVideoCodecVp8(VideoCodecVP8* vp8_settings) const;
    virtual void FillVideoCodecVp9(VideoCodecVP9* vp9_settings) const;
    virtual void FillVideoCodecAv1(VideoCodecAV1* av1_settings) const;

   private:
    ~EncoderSpecificSettings() override {}
    friend class VideoEncoderConfig;
  };

  class Vp8EncoderSpecificSettings : public EncoderSpecificSettings {
   public:
    explicit Vp8EncoderSpecificSettings(const VideoCodecVP8& specifics);
    void FillVideoCodecVp8(VideoCodecVP8* vp8_settings) const override;

   private:
    VideoCodecVP8 specifics_;
  };

  class Vp9EncoderSpecificSettings : public EncoderSpecificSettings {
   public:
    explicit Vp9EncoderSpecificSettings(const VideoCodecVP9& specifics);
    void FillVideoCodecVp9(VideoCodecVP9* vp9_settings) const override;

   private:
    VideoCodecVP9 specifics_;
  };

  class Av1EncoderSpecificSettings : public EncoderSpecificSettings {
   public:
    explicit Av1EncoderSpecificSettings(const VideoCodecAV1& specifics);
    void FillVideoCodecAv1(VideoCodecAV1* av1_settings) const override;

   private:
    VideoCodecAV1 specifics_;
  };

  enum class ContentType {
    kRealtimeVideo,
    kScreen,
  };

  class VideoStreamFactoryInterface : public RefCountInterface {
   public:
    // An implementation should return a std::vector<VideoStream> with the
    // wanted VideoStream settings for the given video resolution.
    // The size of the vector may not be larger than
    // `encoder_config.number_of_streams`.
    virtual std::vector<VideoStream> CreateEncoderStreams(
        const FieldTrialsView& field_trials,
        int frame_width,
        int frame_height,
        const VideoEncoderConfig& encoder_config) = 0;

   protected:
    ~VideoStreamFactoryInterface() override {}
  };

  VideoEncoderConfig& operator=(VideoEncoderConfig&&) = default;
  VideoEncoderConfig& operator=(const VideoEncoderConfig&) = delete;

  // Mostly used by tests.  Avoid creating copies if you can.
  VideoEncoderConfig Copy() const { return VideoEncoderConfig(*this); }

  VideoEncoderConfig();
  VideoEncoderConfig(VideoEncoderConfig&&);
  ~VideoEncoderConfig();
  std::string ToString() const;

  bool HasScaleResolutionDownTo() const;

  // TODO(bugs.webrtc.org/6883): Consolidate on one of these.
  VideoCodecType codec_type;
  SdpVideoFormat video_format;

  // Note: This factory can be unset, and VideoStreamEncoder will
  // then use the EncoderStreamFactory. The factory is only set by
  // tests.
  rtc::scoped_refptr<VideoStreamFactoryInterface> video_stream_factory;
  std::vector<SpatialLayer> spatial_layers;
  ContentType content_type;
  bool frame_drop_enabled;
  rtc::scoped_refptr<const EncoderSpecificSettings> encoder_specific_settings;

  // Padding will be used up to this bitrate regardless of the bitrate produced
  // by the encoder. Padding above what's actually produced by the encoder helps
  // maintaining a higher bitrate estimate. Padding will however not be sent
  // unless the estimated bandwidth indicates that the link can handle it.
  int min_transmit_bitrate_bps;
  int max_bitrate_bps;
  // The bitrate priority used for all VideoStreams.
  double bitrate_priority;

  // The simulcast layer's configurations set by the application for this video
  // sender. These are modified by the video_stream_factory before being passed
  // down to lower layers for the video encoding.
  // `simulcast_layers` is also used for configuring non-simulcast (when there
  // is a single VideoStream).
  // We have the same number of `simulcast_layers` as we have negotiated
  // encodings, for example 3 are used in both simulcast and legacy kSVC.
  std::vector<VideoStream> simulcast_layers;

  // Max number of encoded VideoStreams to produce.
  // This is the same as the number of encodings negotiated (i.e. SSRCs),
  // whether or not those encodings are `active`, except for when legacy kSVC
  // is used. In this case we have three SSRCs but `number_of_streams` is
  // changed to 1 to tell lower layers to limit the number of streams.
  size_t number_of_streams;

  // Legacy Google conference mode flag for simulcast screenshare
  bool legacy_conference_mode;

  // Indicates whether quality scaling can be used or not.
  bool is_quality_scaling_allowed;

  // Maximum Quantization Parameter.
  // This value is fed into EncoderStreamFactory that
  // apply it to all simulcast layers/spatial layers.
  int max_qp;

 private:
  // Access to the copy constructor is private to force use of the Copy()
  // method for those exceptional cases where we do use it.
  VideoEncoderConfig(const VideoEncoderConfig&);
};

}  // namespace webrtc

#endif  // VIDEO_CONFIG_VIDEO_ENCODER_CONFIG_H_