[nageru] / futatabi / player.cpp

#include "player.h"

#include "clip_list.h"
#include "defs.h"
#include "flags.h"
#include "frame_on_disk.h"
#include "jpeg_frame_view.h"
#include "shared/context.h"
#include "shared/ffmpeg_raii.h"
#include "shared/httpd.h"
#include "shared/metrics.h"
#include "shared/mux.h"
#include "shared/timebase.h"
#include "video_stream.h"

#include <algorithm>
#include <chrono>
#include <condition_variable>
#include <movit/util.h>
#include <mutex>
#include <stdio.h>
#include <thread>
#include <vector>

using namespace std;
using namespace std::chrono;

extern HTTPD *global_httpd;

void Player::thread_func(AVFormatContext *file_avctx)
{
        pthread_setname_np(pthread_self(), "Player");

        QSurface *surface = create_surface();
        QOpenGLContext *context = create_context(surface);
        if (!make_current(context, surface)) {
                printf("oops\n");
                abort();
        }

        check_error();

        // Create the VideoStream object, now that we have an OpenGL context.
        if (stream_output != NO_STREAM_OUTPUT) {
                video_stream.reset(new VideoStream(file_avctx));
                video_stream->start();
        }

        check_error();

        while (!should_quit) {
                play_playlist_once();
        }
}

namespace {

double calc_progress(const Clip &clip, int64_t pts)
{
        return double(pts - clip.pts_in) / (clip.pts_out - clip.pts_in);
}

void do_splice(const vector<ClipWithID> &new_list, size_t playing_index1, ssize_t playing_index2, vector<ClipWithID> *old_list)
{
        assert(playing_index2 == -1 || size_t(playing_index2) == playing_index1 + 1);

        // First see if we can do the simple thing; find an element in the new
        // list that we are already playing, which will serve as our splice point.
        int splice_start_new_list = -1;
        for (size_t clip_idx = 0; clip_idx < new_list.size(); ++clip_idx) {
                if (new_list[clip_idx].id == (*old_list)[playing_index1].id) {
                        splice_start_new_list = clip_idx + 1;
                } else if (playing_index2 != -1 && new_list[clip_idx].id == (*old_list)[playing_index2].id) {
                        splice_start_new_list = clip_idx + 1;
                }
        }
        if (splice_start_new_list == -1) {
                // OK, so the playing items are no longer in the new list. Most likely,
                // that means we deleted some range that included them. But the ones
                // before should stay put -- and we don't want to play them. So find
                // the ones that we've already played, and ignore them. Hopefully,
                // they're contiguous; the last one that's not seen will be our cut point.
                //
                // Keeping track of the playlist range explicitly in the UI would remove
                // the need for these heuristics, but it would probably also mean we'd
                // have to lock the playing clip, which sounds annoying.
                unordered_map<uint64_t, size_t> played_ids;
                for (size_t clip_idx = 0; clip_idx < playing_index1; ++old_list) {
                        played_ids.emplace((*old_list)[clip_idx].id, clip_idx);
                }
                for (size_t clip_idx = 0; clip_idx < new_list.size(); ++clip_idx) {
                        if (played_ids.count(new_list[clip_idx].id)) {
                                splice_start_new_list = clip_idx + 1;
                        }
                }

                if (splice_start_new_list == -1) {
                        // OK, we didn't find any matches; the lists are totally distinct.
                        // So probably the entire thing was deleted; leave it alone.
                        return;
                }
        }

        size_t splice_start_old_list = ((playing_index2 == -1) ? playing_index1 : playing_index2) + 1;
        old_list->erase(old_list->begin() + splice_start_old_list, old_list->end());
        old_list->insert(old_list->end(), new_list.begin() + splice_start_new_list, new_list.end());
}

}  // namespace

void Player::play_playlist_once()
{
        vector<ClipWithID> clip_list;
        bool clip_ready;
        steady_clock::time_point before_sleep = steady_clock::now();
        string pause_status;
        float master_speed = 1.0f;

        // Wait until we're supposed to play something.
        {
                unique_lock<mutex> lock(queue_state_mu);
                playing = false;
                clip_ready = new_clip_changed.wait_for(lock, milliseconds(100), [this] {
                        return should_quit || new_clip_ready;
                });
                if (should_quit) {
                        return;
                }
                if (clip_ready) {
                        new_clip_ready = false;
                        playing = true;
                        clip_list = move(queued_clip_list);
                        queued_clip_list.clear();
                        assert(!clip_list.empty());
                        assert(!splice_ready);  // This corner case should have been handled in splice_play().
                } else {
                        pause_status = this->pause_status;
                }
        }

        steady_clock::duration time_slept = steady_clock::now() - before_sleep;
        pts += duration_cast<duration<size_t, TimebaseRatio>>(time_slept).count();

        if (!clip_ready) {
                if (video_stream != nullptr) {
                        ++metric_refresh_frame;
                        string subtitle = "Futatabi " NAGERU_VERSION ";PAUSED;0.000;" + pause_status;
                        video_stream->schedule_refresh_frame(steady_clock::now(), pts, /*display_func=*/nullptr, QueueSpotHolder(),
                                subtitle);
                }
                return;
        }

        should_skip_to_next = false;  // To make sure we don't have a lingering click from before play.
        steady_clock::time_point origin = steady_clock::now();  // TODO: Add a 100 ms buffer for ramp-up?
        int64_t in_pts_origin = clip_list[0].clip.pts_in;
        for (size_t clip_idx = 0; clip_idx < clip_list.size(); ++clip_idx) {
                const Clip *clip = &clip_list[clip_idx].clip;
                const Clip *next_clip = (clip_idx + 1 < clip_list.size()) ? &clip_list[clip_idx + 1].clip : nullptr;
                int64_t out_pts_origin = pts;

                double next_clip_fade_time = -1.0;
                if (next_clip != nullptr) {
                        double duration_this_clip = double(clip->pts_out - in_pts_origin) / TIMEBASE / clip->speed;
                        double duration_next_clip = double(next_clip->pts_out - next_clip->pts_in) / TIMEBASE / clip->speed;
                        next_clip_fade_time = min(min(duration_this_clip, duration_next_clip), clip->fade_time_seconds);
                }

                int stream_idx = clip->stream_idx;

                // Start playing exactly at a frame.
                // TODO: Snap secondary (fade-to) clips in the same fashion
                // so that we don't get jank here).
                {
                        lock_guard<mutex> lock(frame_mu);

                        // Find the first frame such that frame.pts <= in_pts.
                        auto it = find_last_frame_before(frames[stream_idx], in_pts_origin);
                        if (it != frames[stream_idx].end()) {
                                in_pts_origin = it->pts;
                        }
                }

                steady_clock::time_point next_frame_start;
                for (int64_t frameno = 0; !should_quit; ++frameno) {  // Ends when the clip ends.
                        double out_pts = out_pts_origin + TIMEBASE * frameno / global_flags.output_framerate;
                        next_frame_start =
                                origin + microseconds(lrint((out_pts - out_pts_origin) * 1e6 / TIMEBASE));
                        int64_t in_pts = lrint(in_pts_origin + TIMEBASE * frameno * clip->speed * master_speed / global_flags.output_framerate);
                        pts = lrint(out_pts);

                        float new_master_speed = change_master_speed.exchange(0.0f / 0.0f);
                        if (!std::isnan(new_master_speed)) {
                                master_speed = new_master_speed;
                                in_pts_origin = in_pts - TIMEBASE * frameno * clip->speed * master_speed / global_flags.output_framerate;
                                out_pts_origin = out_pts - TIMEBASE * frameno / global_flags.output_framerate;
                        }

                        if (should_skip_to_next.exchange(false)) {  // Test and clear.
                                Clip *clip = &clip_list[clip_idx].clip;  // Get a non-const pointer.
                                clip->pts_out = std::min<int64_t>(clip->pts_out, llrint(in_pts + clip->fade_time_seconds * clip->speed * TIMEBASE));
                        }

                        if (in_pts >= clip->pts_out) {
                                break;
                        }

                        {
                                lock_guard<mutex> lock(queue_state_mu);
                                if (splice_ready) {
                                        if (next_clip == nullptr) {
                                                do_splice(to_splice_clip_list, clip_idx, -1, &clip_list);
                                        } else {
                                                do_splice(to_splice_clip_list, clip_idx, clip_idx + 1, &clip_list);
                                        }
                                        to_splice_clip_list.clear();
                                        splice_ready = false;

                                        // Refresh the clip pointer, since the clip list may have been reallocated.
                                        clip = &clip_list[clip_idx].clip;

                                        // Recompute next_clip and any needed fade times, since the next clip may have changed
                                        // (or we may have gone from no new clip to having one, or the other way).
                                        next_clip = (clip_idx + 1 < clip_list.size()) ? &clip_list[clip_idx + 1].clip : nullptr;
                                        if (next_clip != nullptr) {
                                                double duration_this_clip = double(clip->pts_out - in_pts) / TIMEBASE / clip->speed;
                                                double duration_next_clip = double(next_clip->pts_out - next_clip->pts_in) / TIMEBASE / clip->speed;
                                                next_clip_fade_time = min(min(duration_this_clip, duration_next_clip), clip->fade_time_seconds);
                                        }
                                }
                        }

                        steady_clock::duration time_behind = steady_clock::now() - next_frame_start;
                        if (stream_output != FILE_STREAM_OUTPUT && time_behind >= milliseconds(200)) {
                                fprintf(stderr, "WARNING: %ld ms behind, dropping a frame (no matter the type).\n",
                                        lrint(1e3 * duration<double>(time_behind).count()));
                                ++metric_dropped_unconditional_frame;
                                continue;
                        }

                        // pts not affected by the swapping below.
                        int64_t in_pts_for_progress = in_pts, in_pts_secondary_for_progress = -1;

                        int primary_stream_idx = stream_idx;
                        FrameOnDisk secondary_frame;
                        int secondary_stream_idx = -1;
                        float fade_alpha = 0.0f;
                        double time_left_this_clip = double(clip->pts_out - in_pts) / TIMEBASE / clip->speed;
                        if (next_clip != nullptr && time_left_this_clip <= next_clip_fade_time) {
                                // We're in a fade to the next clip->
                                secondary_stream_idx = next_clip->stream_idx;
                                int64_t in_pts_secondary = lrint(next_clip->pts_in + (next_clip_fade_time - time_left_this_clip) * TIMEBASE * clip->speed);
                                in_pts_secondary_for_progress = in_pts_secondary;
                                fade_alpha = 1.0f - time_left_this_clip / next_clip_fade_time;

                                // If more than half-way through the fade, interpolate the next clip
                                // instead of the current one, since it's more visible.
                                if (fade_alpha >= 0.5f) {
                                        swap(primary_stream_idx, secondary_stream_idx);
                                        swap(in_pts, in_pts_secondary);
                                        fade_alpha = 1.0f - fade_alpha;
                                }

                                FrameOnDisk frame_lower, frame_upper;
                                bool ok = find_surrounding_frames(in_pts_secondary, secondary_stream_idx, &frame_lower, &frame_upper);
                                if (ok) {
                                        secondary_frame = frame_lower;
                                }
                        }

                        // NOTE: None of this will take into account any snapping done below.
                        double clip_progress = calc_progress(*clip, in_pts_for_progress);
                        map<uint64_t, double> progress{ { clip_list[clip_idx].id, clip_progress } };
                        TimeRemaining time_remaining;
                        if (next_clip != nullptr && time_left_this_clip <= next_clip_fade_time) {
                                double next_clip_progress = calc_progress(*next_clip, in_pts_secondary_for_progress);
                                progress[clip_list[clip_idx + 1].id] = next_clip_progress;
                                time_remaining = compute_time_left(clip_list, clip_idx + 1, next_clip_progress);
                        } else {
                                time_remaining = compute_time_left(clip_list, clip_idx, clip_progress);
                        }
                        if (progress_callback != nullptr) {
                                progress_callback(progress, time_remaining);
                        }

                        FrameOnDisk frame_lower, frame_upper;
                        bool ok = find_surrounding_frames(in_pts, primary_stream_idx, &frame_lower, &frame_upper);
                        if (!ok) {
                                break;
                        }

                        // Wait until we should, or (given buffering) can, output the frame.
                        {
                                unique_lock<mutex> lock(queue_state_mu);
                                if (video_stream == nullptr) {
                                        // No queue, just wait until the right time and then show the frame.
                                        new_clip_changed.wait_until(lock, next_frame_start, [this] {
                                                return should_quit || new_clip_ready || override_stream_idx != -1;
                                        });
                                        if (should_quit) {
                                                return;
                                        }
                                } else {
                                        // If the queue is full (which is really the state we'd like to be in),
                                        // wait until there's room for one more frame (ie., one was output from
                                        // VideoStream), or until or until there's a new clip we're supposed to play.
                                        //
                                        // In this case, we don't sleep until next_frame_start; the displaying is
                                        // done by the queue.
                                        new_clip_changed.wait(lock, [this] {
                                                if (num_queued_frames < max_queued_frames) {
                                                        return true;
                                                }
                                                return should_quit || new_clip_ready || override_stream_idx != -1;
                                        });
                                }
                                if (should_quit) {
                                        return;
                                }
                                if (new_clip_ready) {
                                        if (video_stream != nullptr) {
                                                lock.unlock();  // Urg.
                                                video_stream->clear_queue();
                                                lock.lock();
                                        }
                                        return;
                                }
                                // Honor if we got an override request for the camera.
                                if (override_stream_idx != -1) {
                                        stream_idx = override_stream_idx;
                                        override_stream_idx = -1;
                                        continue;
                                }
                        }

                        string subtitle;
                        {
                                stringstream ss;
                                ss.imbue(locale("C"));
                                ss.precision(3);
                                ss << "Futatabi " NAGERU_VERSION ";PLAYING;";
                                ss << fixed << (time_remaining.num_infinite * 86400.0 + time_remaining.t);
                                ss << ";" << format_duration(time_remaining) << " left";
                                subtitle = ss.str();
                        }

                        // If there's nothing to interpolate between, or if interpolation is turned off,
                        // or we're a preview, then just display the frame.
                        if (frame_lower.pts == frame_upper.pts || global_flags.interpolation_quality == 0 || video_stream == nullptr) {
                                display_single_frame(primary_stream_idx, frame_lower, secondary_stream_idx,
                                                     secondary_frame, fade_alpha, next_frame_start, /*snapped=*/false,
                                                     subtitle);
                                continue;
                        }

                        // Snap to input frame: If we can do so with less than 1% jitter
                        // (ie., move less than 1% of an _output_ frame), do so.
                        // TODO: Snap secondary (fade-to) clips in the same fashion.
                        double pts_snap_tolerance = 0.01 * double(TIMEBASE) * clip->speed / global_flags.output_framerate;
                        bool snapped = false;
                        for (FrameOnDisk snap_frame : { frame_lower, frame_upper }) {
                                if (fabs(snap_frame.pts - in_pts) < pts_snap_tolerance) {
                                        display_single_frame(primary_stream_idx, snap_frame, secondary_stream_idx,
                                                             secondary_frame, fade_alpha, next_frame_start, /*snapped=*/true,
                                                             subtitle);
                                        in_pts_origin += snap_frame.pts - in_pts;
                                        snapped = true;
                                        break;
                                }
                        }
                        if (snapped) {
                                continue;
                        }

                        // The snapping above makes us lock to the input framerate, even in the presence
                        // of pts drift, for most typical cases where it's needed, like converting 60 → 2x60
                        // or 60 → 2x59.94. However, there are some corner cases like 25 → 2x59.94, where we'd
                        // get a snap very rarely (in the given case, once every 24 output frames), and by
                        // that time, we'd have drifted out. We could have solved this by changing the overall
                        // speed ever so slightly, but it requires that we know the actual frame rate (which
                        // is difficult in the presence of jitter and missed frames), or at least do some kind
                        // of matching/clustering. Instead, we take the opportunity to lock to in-between rational
                        // points if we can. E.g., if we are converting 60 → 2x60, we would not only snap to
                        // an original frame every other frame; we would also snap to exactly alpha=0.5 every
                        // in-between frame. Of course, we will still need to interpolate, but we get a lot
                        // closer when we actually get close to an original frame. In other words: Snap more
                        // often, but snap less each time. Unless the input and output frame rates are completely
                        // decorrelated with no common factor, of course (e.g. 12.345 → 34.567, which we should
                        // really never see in practice).
                        for (double fraction : { 1.0 / 2.0, 1.0 / 3.0, 2.0 / 3.0, 1.0 / 4.0, 3.0 / 4.0,
                                                 1.0 / 5.0, 2.0 / 5.0, 3.0 / 5.0, 4.0 / 5.0 }) {
                                double subsnap_pts = frame_lower.pts + fraction * (frame_upper.pts - frame_lower.pts);
                                if (fabs(subsnap_pts - in_pts) < pts_snap_tolerance) {
                                        in_pts_origin += lrint(subsnap_pts) - in_pts;
                                        in_pts = lrint(subsnap_pts);
                                        break;
                                }
                        }

                        if (stream_output != FILE_STREAM_OUTPUT && time_behind >= milliseconds(100)) {
                                fprintf(stderr, "WARNING: %ld ms behind, dropping an interpolated frame.\n",
                                        lrint(1e3 * duration<double>(time_behind).count()));
                                ++metric_dropped_interpolated_frame;
                                continue;
                        }

                        double alpha = double(in_pts - frame_lower.pts) / (frame_upper.pts - frame_lower.pts);
                        auto display_func = [this](shared_ptr<Frame> frame) {
                                if (destination != nullptr) {
                                        destination->setFrame(frame);
                                }
                        };
                        if (secondary_stream_idx == -1) {
                                ++metric_interpolated_frame;
                        } else {
                                ++metric_interpolated_faded_frame;
                        }
                        video_stream->schedule_interpolated_frame(
                                next_frame_start, pts, display_func, QueueSpotHolder(this),
                                frame_lower, frame_upper, alpha,
                                secondary_frame, fade_alpha, subtitle);
                        last_pts_played = in_pts;  // Not really needed; only previews use last_pts_played.
                }

                // The clip ended.
                if (should_quit) {
                        return;
                }

                // Start the next clip from the point where the fade went out.
                if (next_clip != nullptr) {
                        origin = next_frame_start;
                        in_pts_origin = next_clip->pts_in + lrint(next_clip_fade_time * TIMEBASE * clip->speed);
                }
        }

        if (done_callback != nullptr) {
                done_callback();
        }
}

void Player::display_single_frame(int primary_stream_idx, const FrameOnDisk &primary_frame, int secondary_stream_idx, const FrameOnDisk &secondary_frame, double fade_alpha, steady_clock::time_point frame_start, bool snapped, const std::string &subtitle)
{
        auto display_func = [this, primary_stream_idx, primary_frame, secondary_frame, fade_alpha] {
                if (destination != nullptr) {
                        destination->setFrame(primary_stream_idx, primary_frame, secondary_frame, fade_alpha);
                }
        };
        if (video_stream == nullptr) {
                display_func();
        } else {
                if (secondary_stream_idx == -1) {
                        // NOTE: We could be increasing unused metrics for previews, but that's harmless.
                        if (snapped) {
                                ++metric_original_snapped_frame;
                        } else {
                                ++metric_original_frame;
                        }
                        video_stream->schedule_original_frame(
                                frame_start, pts, display_func, QueueSpotHolder(this),
                                primary_frame, subtitle);
                } else {
                        assert(secondary_frame.pts != -1);
                        // NOTE: We could be increasing unused metrics for previews, but that's harmless.
                        if (snapped) {
                                ++metric_faded_snapped_frame;
                        } else {
                                ++metric_faded_frame;
                        }
                        video_stream->schedule_faded_frame(frame_start, pts, display_func,
                                                           QueueSpotHolder(this), primary_frame,
                                                           secondary_frame, fade_alpha, subtitle);
                }
        }
        last_pts_played = primary_frame.pts;
}

// Find the frame immediately before and after this point.
bool Player::find_surrounding_frames(int64_t pts, int stream_idx, FrameOnDisk *frame_lower, FrameOnDisk *frame_upper)
{
        lock_guard<mutex> lock(frame_mu);

        // Find the first frame such that frame.pts >= pts.
        auto it = find_last_frame_before(frames[stream_idx], pts);
        if (it == frames[stream_idx].end()) {
                return false;
        }
        *frame_upper = *it;

        // Find the last frame such that in_pts <= frame.pts (if any).
        if (it == frames[stream_idx].begin()) {
                *frame_lower = *it;
        } else {
                *frame_lower = *(it - 1);
        }
        assert(pts >= frame_lower->pts);
        assert(pts <= frame_upper->pts);
        return true;
}

Player::Player(JPEGFrameView *destination, Player::StreamOutput stream_output, AVFormatContext *file_avctx)
        : destination(destination), stream_output(stream_output)
{
        player_thread = thread(&Player::thread_func, this, file_avctx);

        if (stream_output == HTTPD_STREAM_OUTPUT) {
                global_metrics.add("http_output_frames", { { "type", "original" }, { "reason", "edge_frame_or_no_interpolation" } }, &metric_original_frame);
                global_metrics.add("http_output_frames", { { "type", "faded" }, { "reason", "edge_frame_or_no_interpolation" } }, &metric_faded_frame);
                global_metrics.add("http_output_frames", { { "type", "original" }, { "reason", "snapped" } }, &metric_original_snapped_frame);
                global_metrics.add("http_output_frames", { { "type", "faded" }, { "reason", "snapped" } }, &metric_faded_snapped_frame);
                global_metrics.add("http_output_frames", { { "type", "interpolated" } }, &metric_interpolated_frame);
                global_metrics.add("http_output_frames", { { "type", "interpolated_faded" } }, &metric_interpolated_faded_frame);
                global_metrics.add("http_output_frames", { { "type", "refresh" } }, &metric_refresh_frame);
                global_metrics.add("http_dropped_frames", { { "type", "interpolated" } }, &metric_dropped_interpolated_frame);
                global_metrics.add("http_dropped_frames", { { "type", "unconditional" } }, &metric_dropped_unconditional_frame);
        }
}

Player::~Player()
{
        should_quit = true;
        new_clip_changed.notify_all();
        player_thread.join();

        if (video_stream != nullptr) {
                video_stream->stop();
        }
}

void Player::play(const vector<ClipWithID> &clips)
{
        lock_guard<mutex> lock(queue_state_mu);
        new_clip_ready = true;
        queued_clip_list = clips;
        splice_ready = false;
        override_stream_idx = -1;
        new_clip_changed.notify_all();
}

void Player::splice_play(const vector<ClipWithID> &clips)
{
        lock_guard<mutex> lock(queue_state_mu);
        if (new_clip_ready) {
                queued_clip_list = clips;
                assert(!splice_ready);
                return;
        }

        splice_ready = true;
        to_splice_clip_list = clips;  // Overwrite any queued but not executed splice.
}

void Player::override_angle(unsigned stream_idx)
{
        int64_t last_pts;

        // Corner case: If a new clip is waiting to be played, change its stream and then we're done.
        {
                lock_guard<mutex> lock(queue_state_mu);
                if (new_clip_ready) {
                        assert(queued_clip_list.size() == 1);
                        queued_clip_list[0].clip.stream_idx = stream_idx;
                        return;
                }

                // If we are playing a clip, set override_stream_idx, and the player thread will
                // pick it up and change its internal index.
                if (playing) {
                        override_stream_idx = stream_idx;
                        new_clip_changed.notify_all();
                        return;
                }

                // OK, so we're standing still, presumably at the end of a clip.
                // Look at the last frame played (if it exists), and show the closest
                // thing we've got.
                if (last_pts_played < 0) {
                        return;
                }
                last_pts = last_pts_played;
        }

        lock_guard<mutex> lock(frame_mu);
        auto it = find_first_frame_at_or_after(frames[stream_idx], last_pts);
        if (it == frames[stream_idx].end()) {
                return;
        }
        destination->setFrame(stream_idx, *it);
}

void Player::take_queue_spot()
{
        lock_guard<mutex> lock(queue_state_mu);
        ++num_queued_frames;
}

void Player::release_queue_spot()
{
        lock_guard<mutex> lock(queue_state_mu);
        assert(num_queued_frames > 0);
        --num_queued_frames;
        new_clip_changed.notify_all();
}

TimeRemaining compute_time_left(const vector<ClipWithID> &clips, size_t currently_playing_idx, double progress_currently_playing)
{
        // Look at the last clip and then start counting from there.
        TimeRemaining remaining { 0, 0.0 };
        double last_fade_time_seconds = 0.0;
        for (size_t row = currently_playing_idx; row < clips.size(); ++row) {
                const Clip &clip = clips[row].clip;
                double clip_length = double(clip.pts_out - clip.pts_in) / TIMEBASE / clip.speed;
                if (clip_length >= 86400.0) {  // More than one day.
                        ++remaining.num_infinite;
                } else {
                        if (row == currently_playing_idx) {
                                // A clip we're playing: Subtract the part we've already played.
                                remaining.t = clip_length * (1.0 - progress_currently_playing);
                        } else {
                                // A clip we haven't played yet: Subtract the part that's overlapping
                                // with a previous clip (due to fade).
                                remaining.t += max(clip_length - last_fade_time_seconds, 0.0);
                        }
                }
                last_fade_time_seconds = min(clip_length, clip.fade_time_seconds);
        }
        return remaining;
}

string format_duration(TimeRemaining t)
{
        int t_ms = lrint(t.t * 1e3);

        int ms = t_ms % 1000;
        t_ms /= 1000;
        int s = t_ms % 60;
        t_ms /= 60;
        int m = t_ms;

        char buf[256];
        if (t.num_infinite > 1 && t.t > 0.0) {
                snprintf(buf, sizeof(buf), "%zu clips + %d:%02d.%03d", t.num_infinite, m, s, ms);
        } else if (t.num_infinite > 1) {
                snprintf(buf, sizeof(buf), "%zu clips", t.num_infinite);
        } else if (t.num_infinite == 1 && t.t > 0.0) {
                snprintf(buf, sizeof(buf), "%zu clip + %d:%02d.%03d", t.num_infinite, m, s, ms);
        } else if (t.num_infinite == 1) {
                snprintf(buf, sizeof(buf), "%zu clip", t.num_infinite);
        } else {
                snprintf(buf, sizeof(buf), "%d:%02d.%03d", m, s, ms);
        }
        return buf;
}