[nageru] / nageru / mixer.h

#ifndef _MIXER_H
#define _MIXER_H 1

// The actual video mixer, running in its own separate background thread.

#include <assert.h>
#include <epoxy/gl.h>

#undef Success

#include <stdbool.h>
#include <stdint.h>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <cstddef>
#include <functional>
#include <map>
#include <memory>
#include <mutex>
#include <queue>
#include <string>
#include <thread>
#include <vector>

#include <movit/effect.h>
#include <movit/image_format.h>

#include "audio_mixer.h"
#include "bmusb/bmusb.h"
#include "defs.h"
#include "ffmpeg_capture.h"
#include "shared/httpd.h"
#include "input_state.h"
#include "libusb.h"
#include "pbo_frame_allocator.h"
#include "ref_counted_frame.h"
#include "shared/ref_counted_gl_sync.h"
#include "theme.h"
#include "shared/timebase.h"
#include "video_encoder.h"
#include "ycbcr_interpretation.h"

class ALSAOutput;
class ChromaSubsampler;
class DeckLinkOutput;
class MJPEGEncoder;
class QSurface;
class QSurfaceFormat;
class TimecodeRenderer;
class v210Converter;

namespace movit {
class Effect;
class EffectChain;
class ResourcePool;
class YCbCrInput;
}  // namespace movit

// A class to estimate the future jitter. Used in QueueLengthPolicy (see below).
//
// There are many ways to estimate jitter; I've tested a few ones (and also
// some algorithms that don't explicitly model jitter) with different
// parameters on some real-life data in experiments/queue_drop_policy.cpp.
// This is one based on simple order statistics where I've added some margin in
// the number of starvation events; I believe that about one every hour would
// probably be acceptable, but this one typically goes lower than that, at the
// cost of 2–3 ms extra latency. (If the queue is hard-limited to one frame, it's
// possible to get ~10 ms further down, but this would mean framedrops every
// second or so.) The general strategy is: Take the 99.9-percentile jitter over
// last 5000 frames, multiply by two, and that's our worst-case jitter
// estimate. The fact that we're not using the max value means that we could
// actually even throw away very late frames immediately, which means we only
// get one user-visible event instead of seeing something both when the frame
// arrives late (duplicate frame) and then again when we drop.
class JitterHistory {
private:
        static constexpr size_t history_length = 5000;
        static constexpr double percentile = 0.999;
        static constexpr double multiplier = 2.0;

public:
        void register_metrics(const std::vector<std::pair<std::string, std::string>> &labels);
        void unregister_metrics(const std::vector<std::pair<std::string, std::string>> &labels);

        void clear() {
                history.clear();
                orders.clear();
        }
        void frame_arrived(std::chrono::steady_clock::time_point now, int64_t frame_duration, size_t dropped_frames);
        std::chrono::steady_clock::time_point get_expected_next_frame() const { return expected_timestamp; }
        double estimate_max_jitter() const;

private:
        // A simple O(k) based algorithm for getting the k-th largest or
        // smallest element from our window; we simply keep the multiset
        // ordered (insertions and deletions are O(n) as always) and then
        // iterate from one of the sides. If we had larger values of k,
        // we could go for a more complicated setup with two sets or heaps
        // (one increasing and one decreasing) that we keep balanced around
        // the point, or it is possible to reimplement std::set with
        // counts in each node. However, since k=5, we don't need this.
        std::multiset<double> orders;
        std::deque<std::multiset<double>::iterator> history;

        std::chrono::steady_clock::time_point expected_timestamp = std::chrono::steady_clock::time_point::min();

        // Metrics. There are no direct summaries for jitter, since we already have latency summaries.
        std::atomic<int64_t> metric_input_underestimated_jitter_frames{0};
        std::atomic<double> metric_input_estimated_max_jitter_seconds{0.0 / 0.0};
};

// For any card that's not the master (where we pick out the frames as they
// come, as fast as we can process), there's going to be a queue. The question
// is when we should drop frames from that queue (apart from the obvious
// dropping if the 16-frame queue should become full), especially given that
// the frame rate could be lower or higher than the master (either subtly or
// dramatically). We have two (conflicting) demands:
//
//   1. We want to avoid starving the queue.
//   2. We don't want to add more delay than is needed.
//
// Our general strategy is to drop as many frames as we can (helping for #2)
// that we think is safe for #1 given jitter. To this end, we measure the
// deviation from the expected arrival time for all cards, and use that for
// continuous jitter estimation.
//
// We then drop everything from the queue that we're sure we won't need to
// serve the output in the time before the next frame arrives. Typically,
// this means the queue will contain 0 or 1 frames, although more is also
// possible if the jitter is very high.
class QueueLengthPolicy {
public:
        QueueLengthPolicy() {}

        void register_metrics(const std::vector<std::pair<std::string, std::string>> &labels);
        void unregister_metrics(const std::vector<std::pair<std::string, std::string>> &labels);

        // Call after picking out a frame, so 0 means starvation.
        // Note that the policy has no memory; everything is given in as parameters.
        void update_policy(std::chrono::steady_clock::time_point now,
                           std::chrono::steady_clock::time_point expected_next_frame,
                           int64_t input_frame_duration,
                           int64_t master_frame_duration,
                           double max_input_card_jitter_seconds,
                           double max_master_card_jitter_seconds);
        unsigned get_safe_queue_length() const { return safe_queue_length; }

private:
        unsigned safe_queue_length = 0;  // Can never go below zero.

        // Metrics.
        std::atomic<int64_t> metric_input_queue_safe_length_frames{1};
};

class Mixer {
public:
        // The surface format is used for offscreen destinations for OpenGL contexts we need.
        Mixer(const QSurfaceFormat &format);
        ~Mixer();
        void start();
        void quit();

        void transition_clicked(int transition_num);
        void channel_clicked(int preview_num);

        enum Output {
                OUTPUT_LIVE = 0,
                OUTPUT_PREVIEW,
                OUTPUT_INPUT0,  // 1, 2, 3, up to 15 follow numerically.
                NUM_OUTPUTS = 18
        };

        struct DisplayFrame {
                // The chain for rendering this frame. To render a display frame,
                // first wait for <ready_fence>, then call <setup_chain>
                // to wire up all the inputs, and then finally call
                // chain->render_to_screen() or similar.
                movit::EffectChain *chain;
                std::function<void()> setup_chain;

                // Asserted when all the inputs are ready; you cannot render the chain
                // before this.
                RefCountedGLsync ready_fence;

                // Holds on to all the input frames needed for this display frame,
                // so they are not released while still rendering.
                std::vector<RefCountedFrame> input_frames;

                // Textures that should be released back to the resource pool
                // when this frame disappears, if any.
                // TODO: Refcount these as well?
                std::vector<GLuint> temp_textures;
        };
        // Implicitly frees the previous one if there's a new frame available.
        bool get_display_frame(Output output, DisplayFrame *frame) {
                return output_channel[output].get_display_frame(frame);
        }

        // NOTE: Callbacks will be called with a mutex held, so you should probably
        // not do real work in them.
        typedef std::function<void()> new_frame_ready_callback_t;
        void add_frame_ready_callback(Output output, void *key, new_frame_ready_callback_t callback)
        {
                output_channel[output].add_frame_ready_callback(key, callback);
        }

        void remove_frame_ready_callback(Output output, void *key)
        {
                output_channel[output].remove_frame_ready_callback(key);
        }

        // TODO: Should this really be per-channel? Shouldn't it just be called for e.g. the live output?
        typedef std::function<void(const std::vector<std::string> &)> transition_names_updated_callback_t;
        void set_transition_names_updated_callback(Output output, transition_names_updated_callback_t callback)
        {
                output_channel[output].set_transition_names_updated_callback(callback);
        }

        typedef std::function<void(const std::string &)> name_updated_callback_t;
        void set_name_updated_callback(Output output, name_updated_callback_t callback)
        {
                output_channel[output].set_name_updated_callback(callback);
        }

        typedef std::function<void(const std::string &)> color_updated_callback_t;
        void set_color_updated_callback(Output output, color_updated_callback_t callback)
        {
                output_channel[output].set_color_updated_callback(callback);
        }

        std::vector<std::string> get_transition_names()
        {
                return theme->get_transition_names(pts());
        }

        unsigned get_num_channels() const
        {
                return theme->get_num_channels();
        }

        std::string get_channel_name(unsigned channel) const
        {
                return theme->get_channel_name(channel);
        }

        std::string get_channel_color(unsigned channel) const
        {
                return theme->get_channel_color(channel);
        }

        int map_channel_to_signal(unsigned channel) const
        {
                return theme->map_channel_to_signal(channel);
        }

        int map_signal_to_card(int signal)
        {
                return theme->map_signal_to_card(signal);
        }

        unsigned get_master_clock() const
        {
                return master_clock_channel;
        }

        void set_master_clock(unsigned channel)
        {
                master_clock_channel = channel;
        }

        void set_signal_mapping(int signal, int card)
        {
                return theme->set_signal_mapping(signal, card);
        }

        YCbCrInterpretation get_input_ycbcr_interpretation(unsigned card_index) const;
        void set_input_ycbcr_interpretation(unsigned card_index, const YCbCrInterpretation &interpretation);

        bool get_supports_set_wb(unsigned channel) const
        {
                return theme->get_supports_set_wb(channel);
        }

        void set_wb(unsigned channel, double r, double g, double b) const
        {
                theme->set_wb(channel, r, g, b);
        }

        std::string format_status_line(const std::string &disk_space_left_text, double file_length_seconds)
        {
                return theme->format_status_line(disk_space_left_text, file_length_seconds);
        }

        // Note: You can also get this through the global variable global_audio_mixer.
        AudioMixer *get_audio_mixer() { return audio_mixer.get(); }
        const AudioMixer *get_audio_mixer() const { return audio_mixer.get(); }

        void schedule_cut()
        {
                should_cut = true;
        }

        std::string get_card_description(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_description();
        }

        // The difference between this and the previous function is that if a card
        // is used as the current output, get_card_description() will return the
        // fake card that's replacing it for input, whereas this function will return
        // the card's actual name.
        std::string get_output_card_description(unsigned card_index) const {
                assert(card_can_be_used_as_output(card_index));
                assert(card_index < MAX_VIDEO_CARDS);
                if (cards[card_index].parked_capture) {
                        return cards[card_index].parked_capture->get_description();
                } else {
                        return cards[card_index].capture->get_description();
                }
        }

        bool card_can_be_used_as_output(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].output != nullptr && cards[card_index].capture != nullptr;
        }

        bool card_is_cef(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].type == CardType::CEF_INPUT;
        }

        bool card_is_ffmpeg(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                if (cards[card_index].type != CardType::FFMPEG_INPUT) {
                        return false;
                }
#ifdef HAVE_SRT
                // SRT inputs are more like regular inputs than FFmpeg inputs,
                // so show them as such. (This allows the user to right-click
                // to select a different input.)
                return static_cast<FFmpegCapture *>(cards[card_index].capture.get())->get_srt_sock() == -1;
#else
                return true;
#endif
        }

        bool card_is_active(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                std::lock_guard<std::mutex> lock(card_mutex);
                return cards[card_index].capture != nullptr;
        }

        void force_card_active(unsigned card_index)
        {
                // handle_hotplugged_cards() will pick this up.
                std::lock_guard<std::mutex> lock(card_mutex);
                cards[card_index].force_active = true;
        }

        std::map<uint32_t, bmusb::VideoMode> get_available_video_modes(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_available_video_modes();
        }

        uint32_t get_current_video_mode(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_current_video_mode();
        }

        void set_video_mode(unsigned card_index, uint32_t mode) {
                assert(card_index < MAX_VIDEO_CARDS);
                cards[card_index].capture->set_video_mode(mode);
        }

        void start_mode_scanning(unsigned card_index);

        std::map<uint32_t, std::string> get_available_video_inputs(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_available_video_inputs();
        }

        uint32_t get_current_video_input(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_current_video_input();
        }

        void set_video_input(unsigned card_index, uint32_t input) {
                assert(card_index < MAX_VIDEO_CARDS);
                cards[card_index].capture->set_video_input(input);
        }

        std::map<uint32_t, std::string> get_available_audio_inputs(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_available_audio_inputs();
        }

        uint32_t get_current_audio_input(unsigned card_index) const {
                assert(card_index < MAX_VIDEO_CARDS);
                return cards[card_index].capture->get_current_audio_input();
        }

        void set_audio_input(unsigned card_index, uint32_t input) {
                assert(card_index < MAX_VIDEO_CARDS);
                cards[card_index].capture->set_audio_input(input);
        }

        std::string get_ffmpeg_filename(unsigned card_index) const;

        void set_ffmpeg_filename(unsigned card_index, const std::string &filename);

        void change_x264_bitrate(unsigned rate_kbit) {
                video_encoder->change_x264_bitrate(rate_kbit);
        }

        int get_output_card_index() const {  // -1 = no output, just stream.
                return desired_output_card_index;
        }

        void set_output_card(int card_index) { // -1 = no output, just stream.
                desired_output_card_index = card_index;
        }

        std::map<uint32_t, bmusb::VideoMode> get_available_output_video_modes() const;

        uint32_t get_output_video_mode() const {
                return desired_output_video_mode;
        }

        void set_output_video_mode(uint32_t mode) {
                desired_output_video_mode = mode;
        }

        void set_display_timecode_in_stream(bool enable) {
                display_timecode_in_stream = enable;
        }

        void set_display_timecode_on_stdout(bool enable) {
                display_timecode_on_stdout = enable;
        }

        int64_t get_num_connected_clients() const {
                return httpd.get_num_connected_clients();
        }

        Theme::MenuEntry *get_theme_menu() { return theme->get_theme_menu(); }

        void theme_menu_entry_clicked(int lua_ref) { return theme->theme_menu_entry_clicked(lua_ref); }

        void set_theme_menu_callback(std::function<void()> callback)
        {
                theme->set_theme_menu_callback(callback);
        }

        void wait_for_next_frame();

private:
        struct CaptureCard;

        void configure_card(unsigned card_index, bmusb::CaptureInterface *capture, CardType card_type, DeckLinkOutput *output, bool is_srt_card);
        void set_output_card_internal(int card_index);  // Should only be called from the mixer thread.
        void bm_frame(unsigned card_index, uint16_t timecode,
                bmusb::FrameAllocator::Frame video_frame, size_t video_offset, bmusb::VideoFormat video_format,
                bmusb::FrameAllocator::Frame audio_frame, size_t audio_offset, bmusb::AudioFormat audio_format);
        void upload_texture_for_frame(
                int field, bmusb::VideoFormat video_format,
                size_t y_offset, size_t cbcr_offset, size_t video_offset,
                PBOFrameAllocator::Userdata *userdata);
        void bm_hotplug_add(libusb_device *dev);
        void bm_hotplug_remove(unsigned card_index);
        void place_rectangle(movit::Effect *resample_effect, movit::Effect *padding_effect, float x0, float y0, float x1, float y1);
        void thread_func();
        void handle_hotplugged_cards();
        void schedule_audio_resampling_tasks(unsigned dropped_frames, int num_samples_per_frame, int length_per_frame, bool is_preroll, std::chrono::steady_clock::time_point frame_timestamp);
        std::string get_timecode_text() const;
        void render_one_frame(int64_t duration);
        void audio_thread_func();
        void release_display_frame(DisplayFrame *frame);
#ifdef HAVE_SRT
        void start_srt();
#endif
        double pts() { return double(pts_int) / TIMEBASE; }
        void trim_queue(CaptureCard *card, size_t safe_queue_length);
        std::pair<std::string, std::string> get_channels_json();
        std::pair<std::string, std::string> get_channel_color_http(unsigned channel_idx);

        HTTPD httpd;
        unsigned num_video_inputs, num_html_inputs = 0;

        QSurface *mixer_surface, *h264_encoder_surface, *decklink_output_surface, *image_update_surface;
        std::unique_ptr<movit::ResourcePool> resource_pool;
        std::unique_ptr<Theme> theme;
        std::atomic<unsigned> audio_source_channel{0};
        std::atomic<int> master_clock_channel{0};  // Gets overridden by <output_card_index> if set.
        int output_card_index = -1;  // -1 for none.
        uint32_t output_video_mode = -1;

        // The mechanics of changing the output card and modes are so intricately connected
        // with the work the mixer thread is doing. Thus, we don't change it directly,
        // we just set this variable instead, which signals to the mixer thread that
        // it should do the change before the next frame. This simplifies locking
        // considerations immensely.
        std::atomic<int> desired_output_card_index{-1};
        std::atomic<uint32_t> desired_output_video_mode{0};

        std::unique_ptr<movit::EffectChain> display_chain;
        std::unique_ptr<ChromaSubsampler> chroma_subsampler;
        std::unique_ptr<v210Converter> v210_converter;
        std::unique_ptr<VideoEncoder> video_encoder;
        std::unique_ptr<MJPEGEncoder> mjpeg_encoder;

        std::unique_ptr<TimecodeRenderer> timecode_renderer;
        std::atomic<bool> display_timecode_in_stream{false};
        std::atomic<bool> display_timecode_on_stdout{false};

        // Effects part of <display_chain>. Owned by <display_chain>.
        movit::YCbCrInput *display_input;

        int64_t pts_int = 0;  // In TIMEBASE units.

        mutable std::mutex frame_num_mutex;
        std::condition_variable frame_num_updated;
        unsigned frame_num = 0;  // Under <frame_num_mutex>.

        // Accumulated errors in number of 1/TIMEBASE audio samples. If OUTPUT_FREQUENCY divided by
        // frame rate is integer, will always stay zero.
        unsigned fractional_samples = 0;

        // Monotonic counter that lets us know which slot was last turned into
        // a fake capture. Used for SRT re-plugging.
        unsigned fake_capture_counter = 0;

        mutable std::mutex card_mutex;
        bool has_bmusb_thread = false;
        struct CaptureCard {
                // If nullptr, the card is inactive, and will be hidden in the UI.
                // Only fake capture cards can be inactive.
                std::unique_ptr<bmusb::CaptureInterface> capture;
                // If true, card must always be active (typically because it's one of the
                // first cards, or because the theme has explicitly asked for it).
                bool force_active = false;
                bool is_fake_capture;
                // If is_fake_capture is true, contains a monotonic timer value for when
                // it was last changed. Otherwise undefined. Used for SRT re-plugging.
                int fake_capture_counter;
                std::string last_srt_stream_id = "<default, matches nothing>";  // Used for SRT re-plugging.
                CardType type;
                std::unique_ptr<DeckLinkOutput> output;

                // CEF only delivers frames when it actually has a change.
                // If we trim the queue for latency reasons, we could thus
                // end up in a situation trimming a frame that was meant to
                // be displayed for a long time, which is really suboptimal.
                // Thus, if we drop the last frame we have, may_have_dropped_last_frame
                // is set to true, and the next starvation event will trigger
                // us requestin a CEF repaint.
                bool is_cef_capture, may_have_dropped_last_frame = false;

                // If this card is used for output (ie., output_card_index points to it),
                // it cannot simultaneously be uesd for capture, so <capture> gets replaced
                // by a FakeCapture. However, since reconstructing the real capture object
                // with all its state can be annoying, it is not being deleted, just stopped
                // and moved here.
                std::unique_ptr<bmusb::CaptureInterface> parked_capture;

                std::unique_ptr<PBOFrameAllocator> frame_allocator;

                // Stuff for the OpenGL context (for texture uploading).
                QSurface *surface = nullptr;

                struct NewFrame {
                        RefCountedFrame frame;
                        int64_t length;  // In TIMEBASE units.
                        bool interlaced;
                        unsigned field;  // Which field (0 or 1) of the frame to use. Always 0 for progressive.
                        bool texture_uploaded = false;
                        unsigned dropped_frames = 0;  // Number of dropped frames before this one.
                        std::chrono::steady_clock::time_point received_timestamp = std::chrono::steady_clock::time_point::min();
                        movit::RGBTriplet neutral_color{1.0f, 1.0f, 1.0f};

                        // Used for MJPEG encoding, and texture upload.
                        // width=0 or height=0 means a broken frame, ie., do not upload.
                        bmusb::VideoFormat video_format;
                        size_t video_offset, y_offset, cbcr_offset;
                };
                std::deque<NewFrame> new_frames;
                std::condition_variable new_frames_changed;  // Set whenever new_frames is changed.
                QueueLengthPolicy queue_length_policy;  // Refers to the "new_frames" queue.

                std::vector<int32_t> new_raw_audio;

                int last_timecode = -1;  // Unwrapped.

                JitterHistory jitter_history;

                // Metrics.
                std::vector<std::pair<std::string, std::string>> labels;
                std::atomic<int64_t> metric_input_received_frames{0};
                std::atomic<int64_t> metric_input_duped_frames{0};
                std::atomic<int64_t> metric_input_dropped_frames_jitter{0};
                std::atomic<int64_t> metric_input_dropped_frames_error{0};
                std::atomic<int64_t> metric_input_resets{0};
                std::atomic<int64_t> metric_input_queue_length_frames{0};

                std::atomic<int64_t> metric_input_has_signal_bool{-1};
                std::atomic<int64_t> metric_input_is_connected_bool{-1};
                std::atomic<int64_t> metric_input_interlaced_bool{-1};
                std::atomic<int64_t> metric_input_width_pixels{-1};
                std::atomic<int64_t> metric_input_height_pixels{-1};
                std::atomic<int64_t> metric_input_frame_rate_nom{-1};
                std::atomic<int64_t> metric_input_frame_rate_den{-1};
                std::atomic<int64_t> metric_input_sample_rate_hz{-1};

                // SRT metrics.
                std::atomic<double> metric_srt_uptime_seconds{0.0 / 0.0};
                std::atomic<double> metric_srt_send_duration_seconds{0.0 / 0.0};
                std::atomic<int64_t> metric_srt_sent_bytes{-1};
                std::atomic<int64_t> metric_srt_received_bytes{-1};
                std::atomic<int64_t> metric_srt_sent_packets_normal{-1};
                std::atomic<int64_t> metric_srt_received_packets_normal{-1};
                std::atomic<int64_t> metric_srt_sent_packets_lost{-1};
                std::atomic<int64_t> metric_srt_received_packets_lost{-1};
                std::atomic<int64_t> metric_srt_sent_packets_retransmitted{-1};
                std::atomic<int64_t> metric_srt_sent_bytes_retransmitted{-1};
                std::atomic<int64_t> metric_srt_sent_packets_ack{-1};
                std::atomic<int64_t> metric_srt_received_packets_ack{-1};
                std::atomic<int64_t> metric_srt_sent_packets_nak{-1};
                std::atomic<int64_t> metric_srt_received_packets_nak{-1};
                std::atomic<int64_t> metric_srt_sent_packets_dropped{-1};
                std::atomic<int64_t> metric_srt_received_packets_dropped{-1};
                std::atomic<int64_t> metric_srt_sent_bytes_dropped{-1};
                std::atomic<int64_t> metric_srt_received_bytes_dropped{-1};
                std::atomic<int64_t> metric_srt_received_packets_undecryptable{-1};
                std::atomic<int64_t> metric_srt_received_bytes_undecryptable{-1};

                std::atomic<int64_t> metric_srt_filter_received_extra_packets{-1};
                std::atomic<int64_t> metric_srt_filter_received_rebuilt_packets{-1};
                std::atomic<int64_t> metric_srt_filter_received_lost_packets{-1};

                std::atomic<double> metric_srt_packet_sending_period_seconds{0.0 / 0.0};
                std::atomic<int64_t> metric_srt_flow_window_packets{-1};
                std::atomic<int64_t> metric_srt_congestion_window_packets{-1};
                std::atomic<int64_t> metric_srt_flight_size_packets{-1};
                std::atomic<double> metric_srt_rtt_seconds{0.0 / 0.0};
                std::atomic<double> metric_srt_estimated_bandwidth_bits_per_second{0.0 / 0.0};
                std::atomic<double> metric_srt_bandwidth_ceiling_bits_per_second{0.0 / 0.0};
                std::atomic<int64_t> metric_srt_send_buffer_available_bytes{-1};
                std::atomic<int64_t> metric_srt_receive_buffer_available_bytes{-1};
                std::atomic<int64_t> metric_srt_mss_bytes{-1};
                std::atomic<int64_t> metric_srt_sender_unacked_packets{-1};
                std::atomic<int64_t> metric_srt_sender_unacked_bytes{-1};
                std::atomic<double> metric_srt_sender_unacked_timespan_seconds{0.0 / 0.0};
                std::atomic<double> metric_srt_sender_delivery_delay_seconds{0.0 / 0.0};
                std::atomic<int64_t> metric_srt_receiver_unacked_packets{-1};
                std::atomic<int64_t> metric_srt_receiver_unacked_bytes{-1};
                std::atomic<double> metric_srt_receiver_unacked_timespan_seconds{0.0 / 0.0};
                std::atomic<double> metric_srt_receiver_delivery_delay_seconds{0.0 / 0.0};
                std::atomic<int64_t> metric_srt_filter_sent_packets{-1};

        };
        JitterHistory output_jitter_history;
        CaptureCard cards[MAX_VIDEO_CARDS];  // Protected by <card_mutex>.
        YCbCrInterpretation ycbcr_interpretation[MAX_VIDEO_CARDS];  // Protected by <card_mutex>.
        movit::RGBTriplet last_received_neutral_color[MAX_VIDEO_CARDS];  // Used by the mixer thread only. Constructor-initialiezd.
        std::unique_ptr<AudioMixer> audio_mixer;  // Same as global_audio_mixer (see audio_mixer.h).
        bool input_card_is_master_clock(unsigned card_index, unsigned master_card_index) const;
        struct OutputFrameInfo {
                int dropped_frames;  // Since last frame.
                int num_samples;  // Audio samples needed for this output frame.
                int64_t frame_duration;  // In TIMEBASE units.
                bool is_preroll;
                std::chrono::steady_clock::time_point frame_timestamp;
        };
        OutputFrameInfo get_one_frame_from_each_card(unsigned master_card_index, bool master_card_is_output, CaptureCard::NewFrame new_frames[MAX_VIDEO_CARDS], bool has_new_frame[MAX_VIDEO_CARDS], std::vector<int32_t> raw_audio[MAX_VIDEO_CARDS]);

#ifdef HAVE_SRT
        void update_srt_stats(int srt_sock, Mixer::CaptureCard *card);
#endif

        std::string description_for_card(unsigned card_index);
        static bool is_srt_card(const CaptureCard *card);

        InputState input_state;

        // Cards we have been noticed about being hotplugged, but haven't tried adding yet.
        // Protected by its own mutex.
        std::mutex hotplug_mutex;
        std::vector<libusb_device *> hotplugged_cards;
#ifdef HAVE_SRT
        std::vector<int> hotplugged_srt_cards;
#endif

        class OutputChannel {
        public:
                ~OutputChannel();
                void output_frame(DisplayFrame &&frame);
                bool get_display_frame(DisplayFrame *frame);
                void add_frame_ready_callback(void *key, new_frame_ready_callback_t callback);
                void remove_frame_ready_callback(void *key);
                void set_transition_names_updated_callback(transition_names_updated_callback_t callback);
                void set_name_updated_callback(name_updated_callback_t callback);
                void set_color_updated_callback(color_updated_callback_t callback);

        private:
                friend class Mixer;

                unsigned channel;
                Mixer *parent = nullptr;  // Not owned.
                std::mutex frame_mutex;
                DisplayFrame current_frame, ready_frame;  // protected by <frame_mutex>
                bool has_current_frame = false, has_ready_frame = false;  // protected by <frame_mutex>
                std::map<void *, new_frame_ready_callback_t> new_frame_ready_callbacks;  // protected by <frame_mutex>
                transition_names_updated_callback_t transition_names_updated_callback;
                name_updated_callback_t name_updated_callback;
                color_updated_callback_t color_updated_callback;

                std::vector<std::string> last_transition_names;
                std::string last_name, last_color;
        };
        OutputChannel output_channel[NUM_OUTPUTS];

        std::thread mixer_thread;
        std::thread audio_thread;
#ifdef HAVE_SRT
        std::thread srt_thread;
#endif
        std::atomic<bool> should_quit{false};
        std::atomic<bool> should_cut{false};

        std::unique_ptr<ALSAOutput> alsa;

        struct AudioTask {
                int64_t pts_int;
                int num_samples;
                bool adjust_rate;
                std::chrono::steady_clock::time_point frame_timestamp;
        };
        std::mutex audio_mutex;
        std::condition_variable audio_task_queue_changed;
        std::queue<AudioTask> audio_task_queue;  // Under audio_mutex.

        // For mode scanning.
        bool is_mode_scanning[MAX_VIDEO_CARDS]{ false };
        std::vector<uint32_t> mode_scanlist[MAX_VIDEO_CARDS];
        unsigned mode_scanlist_index[MAX_VIDEO_CARDS]{ 0 };
        std::chrono::steady_clock::time_point last_mode_scan_change[MAX_VIDEO_CARDS];
};

extern Mixer *global_mixer;

#endif  // !defined(_MIXER_H)