R6 speed-ramp: ease into slow-motion

A slow-motion shot now decelerates smoothly instead of snapping to slow-mo:
speedRampSetpts builds a log-integrated setpts that ramps playback speed from
normal (1.0) down to below the target across the shot. The shot stays a SINGLE
segment (so the R5 per-shot push-in is preserved) and the existing -t pin keeps
the planned output duration. Normal-speed shots keep a plain constant setpts.
Unit-tested; verified in a real render (payoff carries the ramp, output valid).
Completes R6 (crossfades + speed-ramp).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MPuJXQyAeWpFcTtcnxo1UN

docs/cinematic-quality-rules.md

@@ -41,15 +41,16 @@ Legend: ✅ implemented · ⏳ planned (see `cinematic-highlight-poc-plan.md` P5
 - **Evidence (bowling):** static opening shot measured lowest motion → strongest push (0.117); active
   celebration → gentlest (0.084). Confirmed visually (opening pushes in ~11% over 2s).
 
-## R6 — Transitions: ease, don't jerk — crossfades ✅ / speed-ramp ⏳
-- **Crossfades (DONE):** `xfadeTimelineCommand` dissolves montage beats (video xfade + audio acrossfade)
-  instead of hard-cutting, incl. the cut into the slow-mo payoff. Timeline compresses by (n-1)*xf;
+## R6 — Transitions: ease, don't jerk ✅
+- **Crossfades:** video xfade + audio acrossfade dissolve montage beats instead of hard-cutting. Run as
+  SEPARATE passes then muxed (`xfadeVideoCommand` + `acrossfadeAudioCommand` + `muxCommand`) — one combined
+  filtergraph starves/truncates the audio (that cut the music off early). Timeline compresses by (n-1)*xf;
   `shiftOverlayForCrossfade` re-times overlays and the reported duration is adjusted so overlays/loudness/QA
-  stay aligned. Opt-in via `editing.crossfade-seconds` (0 = hard cuts default; localpoc 0.25), clamped to
-  half the shortest beat. Verified on bowling (visible dissolve, overlay stayed on the payoff).
-- **Speed-ramp into slow-mo (deferred):** easing the playback-speed change itself conflicts with the R5
-  per-shot push-in (sub-segment splitting would reset the zoom); needs a time-varying `setpts` or a push-in
-  that spans sub-segments. The crossfade already softens the *cut* into the payoff.
+  stay aligned. Opt-in via `editing.crossfade-seconds` (0 = hard cuts default; localpoc 0.25).
+- **Speed-ramp into slow-mo:** `speedRampSetpts` gives a slow-mo shot a log-integrated `setpts` that eases the
+  playback speed from normal (1.0) down to below the target across the shot, so the payoff decelerates
+  smoothly instead of snapping. Stays a SINGLE segment (R5 push-in preserved); the `-t` pin keeps the planned
+  duration. Verified on bowling (payoff segment carries the ramp expression; output valid).
 
 ## R7 — Overlays: bold, animated, synced ✅
 - **Rule:** captions are large (fontsize 84), thick-outlined + drop-shadowed for legibility on any background,

src/main/java/org/example/videoclips/editing/HighlightFfmpegRenderer.java

@@ -283,7 +283,7 @@ public class HighlightFfmpegRenderer {
         if (exposureFilter != null && !exposureFilter.isBlank()) {
             filter.append(exposureFilter);   // adaptive per-source exposure normalization, before the grade
         }
-        filter.append(",setpts=PTS/").append(decision.playbackSpeed());
+        filter.append(speedRampSetpts(decision));
         filter.append(cinematicVisualFilter(decision.visualTreatment(), style));
         if (styled) {
             filter.append(",noise=alls=6:allf=t");   // subtle film grain
@@ -902,6 +902,27 @@ public class HighlightFfmpegRenderer {
         return AssetLicensePolicy.read(asset).orElse(AssetLicensePolicy.UNTRACKED);
     }
 
+    /**
+     * The setpts filter for a shot. A slow-motion shot (speed < 0.85) EASES into slow motion: playback speed
+     * ramps from normal (1.0) down to below the target across the shot via a log-integrated setpts expression,
+     * so the payoff decelerates smoothly instead of snapping to slow-mo. The shot stays a single segment (the
+     * R5 push-in is preserved) and the segment's {@code -t} pin keeps the planned output duration. A
+     * normal-speed shot uses a plain constant setpts.
+     */
+    static String speedRampSetpts(EditDecision decision) {
+        double speed = decision.playbackSpeed();
+        if (speed >= 0.85) {
+            return ",setpts=PTS/" + speed;
+        }
+        double din = Math.max(0.1, decision.sourceEndSeconds() - decision.sourceStartSeconds());
+        double s0 = 1.0;
+        double s1 = Math.max(0.2, speed * 0.6);   // end slower than target so the pinned output still fills the beat
+        double k = s1 - s0;
+        // output_seconds = din/(s1-s0) * ln((s0 + (s1-s0)/din * in_seconds)/s0); in_seconds = (PTS-STARTPTS)*TB
+        return ",setpts=(" + fixed(din) + "/(" + fixed(k) + "))*log((" + fixed(s0) + "+(" + fixed(k) + ")/"
+                + fixed(din) + "*(PTS-STARTPTS)*TB)/" + fixed(s0) + ")/TB";
+    }
+
     private String cinematicVisualFilter(String visualTreatment, String style) {
         if (visualTreatment == null || visualTreatment.isBlank() || "none".equalsIgnoreCase(visualTreatment)) {
             return "";

src/test/java/org/example/videoclips/editing/HighlightFfmpegRendererTest.java

@@ -205,6 +205,18 @@ class HighlightFfmpegRendererTest {
         assertThat(portrait).contains("scale=1080:1920").doesNotContain("crop=1080:"); // no letterbox
     }
 
+    @Test
+    void easesIntoSlowMotionOnlyForSlowMoShots() {
+        EditDecision normal = new EditDecision("c", 0, 4, 0, 4, "cut", "cut", 1.0, "hero", "montage");
+        EditDecision slow = new EditDecision("c", 9.2, 11.2, 0, 2.857, "cut", "cut", 0.7, "hero", "montage");
+
+        assertThat(HighlightFfmpegRenderer.speedRampSetpts(normal)).isEqualTo(",setpts=PTS/1.0");
+
+        String ramp = HighlightFfmpegRenderer.speedRampSetpts(slow);
+        assertThat(ramp).contains("setpts=").contains("log(").contains("(PTS-STARTPTS)*TB")
+                .doesNotContain("PTS/0.7");   // ramped, not a constant-speed setpts
+    }
+
     @Test
     void swellsTheMusicTowardThePayoffWhenAPeakIsGiven() {
         HighlightFfmpegRenderer renderer = renderer();