Update app.py

app.py

@@ -938,7 +938,14 @@ def generate(
         chunk_duration = float(chunk_stop) - float(chunk_start)
         if chunk_duration <= 0:
             raise gr.Error("Chunk stop must be after chunk start.")
-        num_frames = snap_frames(chunk_duration)
+        # A momentum-carrying chunk regenerates its own opening `momentum_seconds` from the previous chunk's
+        # tail, which `_trim_head` removes again before appending — so the chunk's own generation has to run
+        # `momentum_seconds` longer than requested, or trimming that regenerated span back off leaves less new
+        # content than the chunk stop/start actually asked for. `snap_frames(momentum)/FPS`, not the raw slider
+        # value, since that's the real, frame-aligned duration `_trailing_frames` actually extracted and
+        # `MiniMaxH3MomentumConditionStep` actually imposed.
+        momentum_seconds = snap_frames(float(momentum)) / FPS if given_video is not None else 0.0
+        num_frames = snap_frames(chunk_duration + momentum_seconds)
 
     skip_recondition = advance and stage_state is not None and not recondition
     if skip_recondition:
@@ -1082,7 +1089,7 @@ def generate(
         # The momentum-imposed opening is a *regeneration* of the previous chunk's own tail, not new content —
         # trimmed here so concatenation doesn't duplicate it. Only continuation chunks that actually had momentum
         # applied carry anything to trim; chunk one, and any chunk that fell back to a plain keyframe carry, don't.
-        chunk_output = _trim_head(path, float(momentum)) if (chunk_advance and given_video is not None) else path
+        chunk_output = _trim_head(path, momentum_seconds) if (chunk_advance and given_video is not None) else path
         chunk_paths = prior_paths + [chunk_output]
         path = _concat_chunks(chunk_paths) if len(chunk_paths) > 1 else chunk_output
         new_chunk_state = {"paths": chunk_paths}