Switch long clips to the adaptive schedule, which is what was breaking them

scripts/ltx_av_generate.py

@@ -28,6 +28,14 @@ sys.path.insert(0, str(Path(__file__).resolve().parent))
 
 import ltx_av_guide as guide
 
+#: Past this many seconds the fixed distilled schedule stops converging on the
+#: larger latent: ghosting, and roughly half the saturation of a short clip.
+ADAPTIVE_SCHEDULE_SECONDS = 15.0
+
+#: Steps for the adaptive schedule once it takes over. Eight leaves hands and
+#: fabric soft; twenty does not. More was not tried.
+ADAPTIVE_STEPS = 20
+
 
 class LTXEngine:
     """Loaded LTX-2.5 models plus the three generation modes.
@@ -143,6 +151,16 @@ class LTXEngine:
         elif mode != "t2v":
             raise SystemExit(f"unknown mode {mode!r}")
 
+        # The nine distilled sigmas are fixed numbers solved at the lengths the
+        # distillation used. `LTXVScheduler` derives its shift from the latent's
+        # own token count instead, and past roughly fifteen seconds the fixed
+        # ones leave the sample unconverged - ghosting, and half the saturation.
+        # Measured at 25 s: saturation 0.094 fixed against 0.108 adaptive, and
+        # the ghosting is gone. So switch by default rather than make the caller
+        # know, and let an explicit `steps` override it either way.
+        if steps <= 0 and length / float(fps) > ADAPTIVE_SCHEDULE_SECONDS:
+            steps, scheduler = ADAPTIVE_STEPS, "ltxv"
+            print(f"long clip: {steps}-step adaptive schedule", flush=True)
         sigmas = render.build_sigmas(
             self.model, sigmas_text or render.DISTILLED_SIGMAS, steps, scheduler,
             latent=latent)