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Diffstat (limited to 'cast/standalone_sender/streaming_vpx_encoder.h')
-rw-r--r-- | cast/standalone_sender/streaming_vpx_encoder.h | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/cast/standalone_sender/streaming_vpx_encoder.h b/cast/standalone_sender/streaming_vpx_encoder.h new file mode 100644 index 00000000..5c99309e --- /dev/null +++ b/cast/standalone_sender/streaming_vpx_encoder.h @@ -0,0 +1,169 @@ +// Copyright 2020 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef CAST_STANDALONE_SENDER_STREAMING_VPX_ENCODER_H_ +#define CAST_STANDALONE_SENDER_STREAMING_VPX_ENCODER_H_ + +#include <vpx/vpx_encoder.h> +#include <vpx/vpx_image.h> + +#include <algorithm> +#include <condition_variable> // NOLINT +#include <functional> +#include <memory> +#include <mutex> +#include <queue> +#include <thread> +#include <vector> + +#include "absl/base/thread_annotations.h" +#include "cast/standalone_sender/streaming_video_encoder.h" +#include "cast/streaming/constants.h" +#include "cast/streaming/frame_id.h" +#include "cast/streaming/rtp_time.h" +#include "platform/api/task_runner.h" +#include "platform/api/time.h" + +namespace openscreen { + +class TaskRunner; + +namespace cast { + +class Sender; + +// Uses libvpx to encode VP8/9 video and streams it to a Sender. Includes +// extensive logic for fine-tuning the encoder parameters in real-time, to +// provide the best quality results given external, uncontrollable factors: +// CPU/network availability, and the complexity of the video frame content. +// +// Internally, a separate encode thread is created and used to prevent blocking +// the main thread while frames are being encoded. All public API methods are +// assumed to be called on the same sequence/thread as the main TaskRunner +// (injected via the constructor). +// +// Usage: +// +// 1. EncodeAndSend() is used to queue-up video frames for encoding and sending, +// which will be done on a best-effort basis. +// +// 2. The client is expected to call SetTargetBitrate() frequently based on its +// own bandwidth estimates and congestion control logic. In addition, a client +// may provide a callback for each frame's encode statistics, which can be used +// to further optimize the user experience. For example, the stats can be used +// as a signal to reduce the data volume (i.e., resolution and/or frame rate) +// coming from the video capture source. +class StreamingVpxEncoder : public StreamingVideoEncoder { + public: + StreamingVpxEncoder(const Parameters& params, + TaskRunner* task_runner, + Sender* sender); + + ~StreamingVpxEncoder(); + + int GetTargetBitrate() const override; + void SetTargetBitrate(int new_bitrate) override; + void EncodeAndSend(const VideoFrame& frame, + Clock::time_point reference_time, + std::function<void(Stats)> stats_callback) override; + + private: + // Syntactic convenience to wrap the vpx_image_t alloc/free API in a smart + // pointer. + struct VpxImageDeleter { + void operator()(vpx_image_t* ptr) const { vpx_img_free(ptr); } + }; + using VpxImageUniquePtr = std::unique_ptr<vpx_image_t, VpxImageDeleter>; + + // Represents the state of one frame encode. This is created in + // EncodeAndSend(), and passed to the encode thread via the |encode_queue_|. + struct WorkUnit { + VpxImageUniquePtr image; + Clock::duration duration; + Clock::time_point reference_time; + RtpTimeTicks rtp_timestamp; + std::function<void(Stats)> stats_callback; + }; + + // Same as WorkUnit, but with additional fields to carry the encode results. + struct WorkUnitWithResults : public WorkUnit { + std::vector<uint8_t> payload; + bool is_key_frame = false; + Stats stats; + }; + + bool is_encoder_initialized() const { return config_.g_threads != 0; } + + // Destroys the VP8 encoder context if it has been initialized. + void DestroyEncoder(); + + // The procedure for the |encode_thread_| that loops, processing work units + // from the |encode_queue_| by calling Encode() until it's time to end the + // thread. + void ProcessWorkUnitsUntilTimeToQuit(); + + // If the |encoder_| is live, attempt reconfiguration to allow it to encode + // frames at a new frame size or target bitrate. If reconfiguration is not + // possible, destroy the existing instance and re-create a new |encoder_| + // instance. + void PrepareEncoder(int width, int height, int target_bitrate); + + // Wraps the complex libvpx vpx_codec_encode() call using inputs from + // |work_unit| and populating results there. + void EncodeFrame(bool force_key_frame, WorkUnitWithResults& work_unit); + + // Computes and populates |work_unit.stats| after the last call to + // EncodeFrame(). + void ComputeFrameEncodeStats(Clock::duration encode_wall_time, + int target_bitrate, + WorkUnitWithResults& work_unit); + + // Assembles and enqueues an EncodedFrame with the Sender on the main thread. + void SendEncodedFrame(WorkUnitWithResults results); + + // Allocates a vpx_image_t and copies the content from |frame| to it. + static VpxImageUniquePtr CloneAsVpxImage(const VideoFrame& frame); + + // The reference time of the first frame passed to EncodeAndSend(). + Clock::time_point start_time_ = Clock::time_point::min(); + + // The RTP timestamp of the last frame that was pushed into the + // |encode_queue_| by EncodeAndSend(). This is used to check whether + // timestamps are monotonically increasing. + RtpTimeTicks last_enqueued_rtp_timestamp_; + + // Guards a few members shared by both the main and encode threads. + std::mutex mutex_; + + // Used by the encode thread to sleep until more work is available. + std::condition_variable cv_ ABSL_GUARDED_BY(mutex_); + + // These encode parameters not passed in the WorkUnit struct because it is + // desirable for them to be applied as soon as possible, with the very next + // WorkUnit popped from the |encode_queue_| on the encode thread, and not to + // wait until some later WorkUnit is processed. + bool needs_key_frame_ ABSL_GUARDED_BY(mutex_) = true; + int target_bitrate_ ABSL_GUARDED_BY(mutex_) = 2 << 20; // Default: 2 Mbps. + + // The queue of frame encodes. The size of this queue is implicitly bounded by + // EncodeAndSend(), where it checks for the total in-flight media duration and + // maybe drops a frame. + std::queue<WorkUnit> encode_queue_ ABSL_GUARDED_BY(mutex_); + + // Current VP8 encoder configuration. Most of the fields are unchanging, and + // are populated in the ctor; but thereafter, only the encode thread accesses + // this struct. + // + // The speed setting is controlled via a separate libvpx API (see members + // below). + vpx_codec_enc_cfg_t config_{}; + + // libvpx VP8/9 encoder instance. Only the encode thread accesses this. + vpx_codec_ctx_t encoder_; +}; + +} // namespace cast +} // namespace openscreen + +#endif // CAST_STANDALONE_SENDER_STREAMING_VPX_ENCODER_H_ |