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* Copyright (c) 2018 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.
#include <memory>
#include <vector>
namespace webrtc {
// Some notes on the prerequisites of the TemporalLayers interface.
// * Vp8TemporalLayers is not thread safe, synchronization is the caller's
// responsibility.
// * The encoder is assumed to encode all frames in order, and callbacks to
// PopulateCodecSpecific() / FrameEncoded() must happen in the same order.
// This means that in the case of pipelining encoders, it is OK to have a chain
// of calls such as this:
// - UpdateLayerConfig(timestampA)
// - UpdateLayerConfig(timestampB)
// - PopulateCodecSpecific(timestampA, ...)
// - UpdateLayerConfig(timestampC)
// - OnEncodeDone(timestampA, 1234, ...)
// - UpdateLayerConfig(timestampC)
// - OnEncodeDone(timestampB, 0, ...)
// - OnEncodeDone(timestampC, 1234, ...)
// Note that UpdateLayerConfig() for a new frame can happen before
// FrameEncoded() for a previous one, but calls themselves must be both
// synchronized (e.g. run on a task queue) and in order (per type).
// Two different flavors of temporal layers are currently available:
// kFixedPattern uses a fixed repeating pattern of 1-4 layers.
// kBitrateDynamic can allocate frames dynamically to 1 or 2 layers, based on
// the bitrate produced.
enum class Vp8TemporalLayersType { kFixedPattern, kBitrateDynamic };
struct CodecSpecificInfoVP8;
struct Vp8EncoderConfig {
static constexpr size_t kMaxPeriodicity = 16;
static constexpr size_t kMaxLayers = 5;
// Number of active temporal layers. Set to 0 if not used.
uint32_t ts_number_layers;
// Arrays of length |ts_number_layers|, indicating (cumulative) target bitrate
// and rate decimator (e.g. 4 if every 4th frame is in the given layer) for
// each active temporal layer, starting with temporal id 0.
uint32_t ts_target_bitrate[kMaxLayers];
uint32_t ts_rate_decimator[kMaxLayers];
// The periodicity of the temporal pattern. Set to 0 if not used.
uint32_t ts_periodicity;
// Array of length |ts_periodicity| indicating the sequence of temporal id's
// to assign to incoming frames.
uint32_t ts_layer_id[kMaxPeriodicity];
// Target bitrate, in bps.
uint32_t rc_target_bitrate;
// Clamp QP to min/max. Use 0 to disable clamping.
uint32_t rc_min_quantizer;
uint32_t rc_max_quantizer;
// Defined bit-maskable reference to the three buffers available in VP8.
enum class Vp8BufferReference : uint8_t {
kNone = 0,
kLast = 1,
kGolden = 2,
kAltref = 4
// This interface defines a way of getting the encoder settings needed to
// realize a temporal layer structure.
class Vp8TemporalLayers {
enum BufferFlags : int {
kNone = 0,
kReference = 1,
kUpdate = 2,
kReferenceAndUpdate = kReference | kUpdate,
enum FreezeEntropy { kFreezeEntropy };
struct FrameConfig {
FrameConfig(BufferFlags last, BufferFlags golden, BufferFlags arf);
FrameConfig(BufferFlags last,
BufferFlags golden,
BufferFlags arf,
bool drop_frame;
BufferFlags last_buffer_flags;
BufferFlags golden_buffer_flags;
BufferFlags arf_buffer_flags;
// The encoder layer ID is used to utilize the correct bitrate allocator
// inside the encoder. It does not control references nor determine which
// "actual" temporal layer this is. The packetizer temporal index determines
// which layer the encoded frame should be packetized into.
// Normally these are the same, but current temporal-layer strategies for
// screenshare use one bitrate allocator for all layers, but attempt to
// packetize / utilize references to split a stream into multiple layers,
// with different quantizer settings, to hit target bitrate.
// TODO(pbos): Screenshare layers are being reconsidered at the time of
// writing, we might be able to remove this distinction, and have a temporal
// layer imply both (the normal case).
int encoder_layer_id;
int packetizer_temporal_idx;
bool layer_sync;
bool freeze_entropy;
// Indicates in which order the encoder should search the reference buffers
// when doing motion prediction. Set to kNone to use unspecified order. Any
// buffer indicated here must not have the corresponding no_ref bit set.
// If all three buffers can be reference, the one not listed here should be
// searched last.
Vp8BufferReference first_reference;
Vp8BufferReference second_reference;
FrameConfig(BufferFlags last,
BufferFlags golden,
BufferFlags arf,
bool freeze_entropy);
virtual ~Vp8TemporalLayers() = default;
// If this method returns true, the encoder is free to drop frames for
// instance in an effort to uphold encoding bitrate.
// If this return false, the encoder must not drop any frames unless:
// 1. Requested to do so via FrameConfig.drop_frame
// 2. The frame to be encoded is requested to be a keyframe
// 3. The encoded detected a large overshoot and decided to drop and then
// re-encode the image at a low bitrate. In this case the encoder should
// call OnEncodeDone() once with size = 0 to indicate drop, and then call
// OnEncodeDone() again when the frame has actually been encoded.
virtual bool SupportsEncoderFrameDropping() const = 0;
// New target bitrate, per temporal layer.
virtual void OnRatesUpdated(const std::vector<uint32_t>& bitrates_bps,
int framerate_fps) = 0;
// Called by the encoder before encoding a frame. |cfg| contains the current
// configuration. If the TemporalLayers instance wishes any part of that
// to be changed before the encode step, |cfg| should be changed and then
// return true. If false is returned, the encoder will proceed without
// updating the configuration.
virtual bool UpdateConfiguration(Vp8EncoderConfig* cfg) = 0;
// Returns the recommended VP8 encode flags needed, and moves the temporal
// pattern to the next frame.
// The timestamp may be used as both a time and a unique identifier, and so
// the caller must make sure no two frames use the same timestamp.
// The timestamp uses a 90kHz RTP clock.
// After calling this method, first call the actual encoder with the provided
// frame configuration, and then OnEncodeDone() below.
virtual FrameConfig UpdateLayerConfig(uint32_t rtp_timestamp) = 0;
// Called after the encode step is done. |rtp_timestamp| must match the
// parameter use in the UpdateLayerConfig() call.
// |is_keyframe| must be true iff the encoder decided to encode this frame as
// a keyframe.
// If the encoder decided to drop this frame, |size_bytes| must be set to 0,
// otherwise it should indicate the size in bytes of the encoded frame.
// If |size_bytes| > 0, and |vp8_info| is not null, the TemporalLayers
// instance my update |vp8_info| with codec specific data such as temporal id.
// Some fields of this struct may have already been populated by the encoder,
// check before overwriting.
// If |size_bytes| > 0, |qp| should indicate the frame-level QP this frame was
// encoded at. If the encoder does not support extracting this, |qp| should be
// set to 0.
virtual void OnEncodeDone(uint32_t rtp_timestamp,
size_t size_bytes,
bool is_keyframe,
int qp,
CodecSpecificInfoVP8* vp8_info) = 0;
} // namespace webrtc