initial commit

playback.py

@@ -0,0 +1,17 @@
+"""Playback helpers — selecting and cycling through frames by label."""
+
+
+def frames_with_label(assignments: dict, label: str) -> list:
+    """Sorted frame indices assigned the given label."""
+    return sorted(i for i, lbl in assignments.items() if lbl == label)
+
+
+def next_in_cycle(indices: list, current: int, delta: int) -> int:
+    """Next index in `indices` after `current`, wrapping around.
+
+    If `current` isn't in the set, returns the first index.
+    """
+    if current in indices:
+        pos = indices.index(current)
+        return indices[(pos + delta) % len(indices)]
+    return indices[0]