Reels: fix steppy fade (fps before fade) and ease the expression bump

The fade looked steppy/low-frame-rate because the filtergraph normalized
fps AFTER the fade filters: the brightness ramp was sampled at the looped
still's coarse input cadence, then duplicated up to 30fps. Move fps ahead
of the fades, pin the still's input framerate (-framerate), and force CFR
output (-r) so the dip ramps across a full 30 frames and plays steadily.

Ease narration expressiveness from 0.7 to 0.6 (still tunable via
REEL_TTS_EXAGGERATION). Bump RENDER_VERSION so existing reels re-render.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/reels/render.rs

@@ -87,15 +87,20 @@ pub fn segment_filtergraph(opts: &SegmentOpts, duration: f64) -> String {
     // Fade-out begins one fade-length before the end; clamp so a floor-length
     // segment still gets a valid (non-negative) start time.
     let fade_out_start = (duration - FADE_SECONDS).max(0.0);
+    // `fps` is normalized BEFORE the fades so the brightness ramp is computed
+    // on a true {fps}-frame timeline. If fps came after, the fade would be
+    // sampled at the looped still's coarse input cadence and then duplicated up
+    // to {fps}, which reads as a steppy / low-frame-rate dip.
     format!(
         "[0:v]split=2[bg][fg];\
          [bg]scale={w}:{h}:force_original_aspect_ratio=increase,\
          crop={w}:{h},boxblur=20:2[bgb];\
          [fg]scale={w}:{h}:force_original_aspect_ratio=decrease[fgs];\
          [bgb][fgs]overlay=(W-w)/2:(H-h)/2,\
+         fps={fps},\
          fade=t=in:st=0:d={FADE_SECONDS},\
          fade=t=out:st={fade_out_start:.3}:d={FADE_SECONDS},\
-         setsar=1,fps={fps},format=yuv420p[v];\
+         setsar=1,format=yuv420p[v];\
          [1:a]apad[a]"
     )
 }
@@ -134,11 +139,16 @@ pub fn build_segment_args(
     duration: f64,
     opts: &SegmentOpts,
 ) -> Vec<String> {
+    let fps = opts.fps.to_string();
     let mut args: Vec<String> = vec!["-y".into()];
     if opts.nvenc {
         args.extend(["-hwaccel".into(), "cuda".into()]);
     }
     args.extend([
+        // Read the looped still at the target rate so frames exist for the
+        // fade to ramp across (paired with the in-graph `fps` and CFR output).
+        "-framerate".into(),
+        fps.clone(),
         "-loop".into(),
         "1".into(),
         "-i".into(),
@@ -153,6 +163,10 @@ pub fn build_segment_args(
         "[a]".into(),
         "-t".into(),
         format!("{duration:.3}"),
+        // Force constant frame rate so the segment (and the concatenated reel)
+        // plays at a steady {fps} rather than a variable cadence.
+        "-r".into(),
+        fps,
     ]);
     args.extend(video_encoder_args(opts.nvenc));
     args.extend(
@@ -297,6 +311,16 @@ mod tests {
         assert!(g.contains("fade=t=out:st=3.650:d=0.35"));
     }
 
+    #[test]
+    fn filtergraph_normalizes_fps_before_fading() {
+        // The fps filter must precede the fades, else the brightness ramp is
+        // sampled at the still's coarse cadence and looks steppy.
+        let g = segment_filtergraph(&SegmentOpts::default(), 4.0);
+        let fps_at = g.find("fps=30").expect("fps in graph");
+        let fade_at = g.find("fade=t=in").expect("fade in graph");
+        assert!(fps_at < fade_at);
+    }
+
     #[test]
     fn filtergraph_fade_out_start_never_negative_at_floor() {
         // A floor-length segment shorter than a fade still yields st >= 0.
@@ -314,10 +338,12 @@ mod tests {
             &SegmentOpts::default(),
         );
         let joined = args.join(" ");
-        assert!(joined.contains("-loop 1 -i /img.jpg"));
+        assert!(joined.contains("-framerate 30 -loop 1 -i /img.jpg"));
         assert!(joined.contains("-i /a.wav"));
         assert!(joined.contains("apad"));
         assert!(joined.contains("-t 4.000"));
+        // Constant frame rate forced on the output.
+        assert!(joined.contains("-r 30"));
         assert!(joined.contains("libx264"));
         assert!(joined.ends_with("/out.mp4"));
     }