From a39b2bf47a70559ca8bcad2b2d178fadfe68688c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Krystian=20Bac=C5=82awski?= <krystian.baclawski@gmail.com>
Date: Tue, 4 Apr 2023 22:46:28 +0200
Subject: [PATCH] Make sync track compress better (backported from 88834b8)

* Delta encoding for sync track frames.
* Fix non-monotonic track frames
---
 lib/libmisc/sync.c   | 13 +++++++++++++
 tools/sync2c/main.go | 18 +++++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/lib/libmisc/sync.c b/lib/libmisc/sync.c
index 06c3cc7e..2a4ae770 100644
--- a/lib/libmisc/sync.c
+++ b/lib/libmisc/sync.c
@@ -28,6 +28,19 @@ void TrackInit(TrackT *track) {
   track->type = TRACK_LINEAR;
   track->pending = true;
 
+  {
+    short prevFrame = -1;
+    TrackKeyT *curr;
+
+    for (curr = track->data; curr->frame != END_KEY; curr++) {
+      if (curr->frame < 0)
+        continue;
+      if (prevFrame >= 0)
+        curr->frame += prevFrame;
+      prevFrame = curr->frame;
+    }
+  }
+
   TrackAdvance(track, track->data);
 }
 
diff --git a/tools/sync2c/main.go b/tools/sync2c/main.go
index acaf08ae..b59a4235 100644
--- a/tools/sync2c/main.go
+++ b/tools/sync2c/main.go
@@ -82,6 +82,18 @@ func parseFrame(token string) (frame int64, err error) {
 		}
 	}
 
+	if prevFrame >= 0 {
+		delta := frame - prevFrame
+		if delta < 0 {
+			return 0, &parseError{
+				"frame numbers must be specified in ascending order"}
+		}
+		prevFrame = frame
+		frame = delta
+	} else {
+		prevFrame = frame
+	}
+
 	return frame, err
 }
 
@@ -89,6 +101,8 @@ func parseValue(token string) (value int64, err error) {
 	return strconv.ParseInt(token, 0, 16)
 }
 
+var prevFrame int64
+
 func parseTrack(tokens []string, track *Track) (err error) {
 	var frame, value int64
 
@@ -105,9 +119,6 @@ func parseTrack(tokens []string, track *Track) (err error) {
 	if value, err = parseValue(tokens[1]); err != nil {
 		return err
 	}
-	if track.First != nil && track.First.Key > int(frame) {
-		return &parseError{"frame numbers must be specified in ascending order"}
-	}
 
 	if len(tokens) == 3 && tokens[2][0] == '!' {
 		typ := tokens[2][1:]
@@ -167,6 +178,7 @@ func parseSyncFile(path string) []Track {
 
 		// Create new track
 		if tokens[0] == "@track" {
+			prevFrame = -1
 			track = &Track{RawName: tokens[1]}
 			continue
 		}