From: Steinar H. Gunderson <steinar+nageru@gunderson.no>
Date: Mon, 21 Oct 2019 19:32:34 +0000 (+0200)
Subject: Fix some jerkiness when playing back with no interpolation.
X-Git-Tag: 1.9.1~8
X-Git-Url: https://git.sesse.net/?p=nageru;a=commitdiff_plain;h=f014bc9a81cc4fae068172a84f0491efef38135e

Fix some jerkiness when playing back with no interpolation.

When hitting a frame exactly, we'd choose [pts_of_previous_frame, pts]
as our candidate range, and always pick the lower. This would make us
jerk around a lot, which would be a particular problem with audio.

Fix by taking a two-pronged approach: First, if we hit a frame exactly,
just send [pts,pts]. Second, activate snapping even when interpolation
is off.

We still have a problem when playing back audio in the case of dropped
video frames (we'll output the same audio twice), but better audio
handling is somewhat outside the scope of this commit.
---

diff --git a/futatabi/player.cpp b/futatabi/player.cpp
index 779e685..4421449 100644
--- a/futatabi/player.cpp
+++ b/futatabi/player.cpp
@@ -355,15 +355,6 @@ void Player::play_playlist_once()
 				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, play_audio);
-				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.
@@ -383,6 +374,15 @@ void Player::play_playlist_once()
 				continue;
 			}
 
+			// 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, play_audio);
+				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
@@ -487,6 +487,7 @@ void Player::display_single_frame(int primary_stream_idx, const FrameOnDisk &pri
 }
 
 // Find the frame immediately before and after this point.
+// If we have an exact match, return it immediately.
 bool Player::find_surrounding_frames(int64_t pts, int stream_idx, FrameOnDisk *frame_lower, FrameOnDisk *frame_upper)
 {
 	lock_guard<mutex> lock(frame_mu);
@@ -498,6 +499,12 @@ bool Player::find_surrounding_frames(int64_t pts, int stream_idx, FrameOnDisk *f
 	}
 	*frame_upper = *it;
 
+	// If we have an exact match, return it immediately.
+	if (frame_upper->pts == pts) {
+		*frame_lower = *it;
+		return true;
+	}
+
 	// Find the last frame such that in_pts <= frame.pts (if any).
 	if (it == frames[stream_idx].begin()) {
 		*frame_lower = *it;