From ffee7085424918edf4b340ca120ece4ddca639ef Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Mon, 16 Mar 2020 23:00:50 +0100 Subject: [PATCH] Stretch the ease length to get back into the right cadence. Unless the speed change is very small, we can stretch the ease a bit (from the default 200 ms into anything in the [0,2] second range) such that we conveniently hit an original frame. This means that if we go into a speed such as 100% or 200%, we've got a very high likelyhood of going into a locked cadence, with the associated quality and performance benefits. --- futatabi/player.cpp | 97 +++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 93 insertions(+), 4 deletions(-) diff --git a/futatabi/player.cpp b/futatabi/player.cpp index c5581b4..b905be0 100644 --- a/futatabi/player.cpp +++ b/futatabi/player.cpp @@ -149,6 +149,11 @@ public: } void snap_by(int64_t offset) { + if (in_easing) { + // Easing will normally aim for a snap at the very end, + // so don't disturb it by jittering during the ease. + return; + } origin.in_pts += offset; } @@ -162,7 +167,9 @@ public: // about 200 ms. This is a simple linear ramp; I tried various forms of // Bézier curves for more elegant/dramatic changing, but it seemed linear // looked just as good in practical video. - void start_easing(double new_master_speed, Instant now); + void start_easing(double new_master_speed, int64_t length_out_pts, Instant now); + + int64_t find_easing_length(double master_speed_target, int64_t length_out_pts, const vector &frames, Instant now); private: // Find out how far we are into the easing curve (0..1). @@ -179,7 +186,7 @@ private: bool in_easing = false; int64_t ease_started_pts = 0; double master_speed_ease_target; - static constexpr int64_t ease_length_out_pts = TIMEBASE / 5; // 200 ms. + int64_t ease_length_out_pts = 0; }; TimelineTracker::Instant TimelineTracker::advance_to_frame(int64_t frameno) @@ -220,7 +227,7 @@ void TimelineTracker::change_master_speed(double new_master_speed, Instant now) origin = now; } -void TimelineTracker::start_easing(double new_master_speed, Instant now) +void TimelineTracker::start_easing(double new_master_speed, int64_t length_out_pts, Instant now) { if (in_easing) { // Apply whatever we managed to complete of the previous easing. @@ -231,6 +238,7 @@ void TimelineTracker::start_easing(double new_master_speed, Instant now) in_easing = true; ease_started_pts = now.out_pts; master_speed_ease_target = new_master_speed; + ease_length_out_pts = length_out_pts; } double TimelineTracker::find_ease_t(double out_pts) const @@ -249,6 +257,85 @@ double TimelineTracker::easing_out_pts_adjustment(double out_pts) const return val; } +int64_t TimelineTracker::find_easing_length(double master_speed_target, int64_t desired_length_out_pts, const vector &frames, Instant now) +{ + // Find out what frame we would have hit (approximately) with the given ease length. + double in_pts_length = 0.5 * (master_speed_target + master_speed) * desired_length_out_pts * clip->speed; + const int input_frame_num = distance( + frames.begin(), + find_first_frame_at_or_after(frames, lrint(now.in_pts + in_pts_length))); + + // Round length_out_pts to the nearest amount of whole frames. + const double frame_length = TIMEBASE / global_flags.output_framerate; + const int length_out_frames = lrint(desired_length_out_pts / frame_length); + + // Time the easing so that we aim at 200 ms (or whatever length_out_pts + // was), but adjust it so that we hit exactly on a frame. Unless we are + // somehow unlucky and run in the middle of a bad fade, this should + // lock us nicely into a cadence where we hit original frames (of course + // assuming the new speed is a reasonable ratio). + // + // Assume for a moment that we are easing into a slowdown, and that + // we're slightly too late to hit the frame we want to. This means that + // we can shorten the ease a bit; this chops some of the total integrated + // velocity and arrive at the frame a bit sooner. Solve for the time + // we want to shorten the ease by (let's call it x, where the original + // length of the ease is called len) such that we hit exactly the in + // pts at the right time: + // + // 0.5 * (mst + ms) * (len - x) * cs + mst * x * cs = desired_len_in_pts + // + // gives + // + // x = (2 * desired_len_in_pts / cs - (mst + ms) * len) / (mst - ms) + // + // Conveniently, this holds even if we are too early; a negative x + // (surprisingly!) gives a lenghtening such that we don't hit the desired + // frame, but hit one slightly later. (x larger than len means that + // it's impossible to hit the desired frame, even if we dropped the ease + // altogether and just changed speeds instantly.) We also have sign invariance, + // so that these properties hold even if we are speeding up, not slowing + // down. Together, these two properties mean that we can cast a fairly + // wide net, trying various input and output frames and seeing which ones + // can be matched up with a minimal change to easing time. (This lets us + // e.g. end the ease close to the midpoint between two endpoint frames + // even if we don't know the frame rate, or deal fairly robustly with + // dropped input frames.) Many of these will give us the same answer, + // but that's fine, because the ease length is the only output. + int64_t best_length_out_pts = TIMEBASE * 10; // Infinite. + for (int output_frame_offset = -2; output_frame_offset <= 2; ++output_frame_offset) { + int64_t aim_length_out_pts = lrint((length_out_frames + output_frame_offset) * frame_length); + if (aim_length_out_pts < 0) { + continue; + } + + for (int input_frame_offset = -2; input_frame_offset <= 2; ++input_frame_offset) { + if (input_frame_num + input_frame_offset < 0 || + input_frame_num + input_frame_offset >= int(frames.size())) { + continue; + } + const int64_t in_pts = frames[input_frame_num + input_frame_offset].pts; + double shorten_by_out_pts = (2.0 * (in_pts - now.in_pts) / clip->speed - (master_speed_target + master_speed) * aim_length_out_pts) / (master_speed_target - master_speed); + int64_t length_out_pts = lrint(aim_length_out_pts - shorten_by_out_pts); + + if (length_out_pts >= 0 && + abs(length_out_pts - desired_length_out_pts) < abs(best_length_out_pts - desired_length_out_pts)) { + best_length_out_pts = length_out_pts; + } + } + } + + // If we need more than two seconds of easing, we give up -- + // this can happen if we're e.g. going from 101% to 100%. + // If so, it would be better to let other mechanisms, such as the switch + // to the next clip, deal with getting us back into sync. + if (best_length_out_pts > TIMEBASE * 2) { + return desired_length_out_pts; + } else { + return best_length_out_pts; + } +} + } // namespace void Player::play_playlist_once() @@ -339,7 +426,9 @@ void Player::play_playlist_once() float new_master_speed = change_master_speed.exchange(0.0f / 0.0f); if (!std::isnan(new_master_speed) && !timeline.in_master_speed(new_master_speed)) { - timeline.start_easing(new_master_speed, instant); + int64_t ease_length_out_pts = TIMEBASE / 5; // 200 ms. + int64_t recommended_pts_length = timeline.find_easing_length(new_master_speed, ease_length_out_pts, frames[clip->stream_idx], instant); + timeline.start_easing(new_master_speed, recommended_pts_length, instant); } if (should_skip_to_next.exchange(false)) { // Test and clear. -- 2.39.2