3 files changed, 29 insertions, 2 deletions
diff --git a/source/blender/blenkernel/BKE_action.h b/source/blender/blenkernel/BKE_action.h
index 763e540fdd9..6d457ed32f0 100644
--- a/source/blender/blenkernel/BKE_action.h
+++ b/source/blender/blenkernel/BKE_action.h
@@ -91,6 +91,10 @@ short action_get_item_transforms(struct bAction *act,
 /* Some kind of bounding box operation on the action */
 void calc_action_range(const struct bAction *act, float *start, float *end, short incl_modifiers);
 
+/* Retrieve the intended playback frame range, using the manually set range if available,
+ * or falling back to scanning F-Curves for their first & last frames otherwise. */
+void BKE_action_get_frame_range(const struct bAction *act, float *r_start, float *r_end);
+
 /* Does action have any motion data at all? */
 bool action_has_motion(const struct bAction *act);
 
diff --git a/source/blender/blenkernel/intern/action.c b/source/blender/blenkernel/intern/action.c
index 27873f19977..47db5183e76 100644
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -1573,6 +1573,24 @@ void calc_action_range(const bAction *act, float *start, float *end, short incl_
   }
 }
 
+/* Retrieve the intended playback frame range, using the manually set range if available,
+ * or falling back to scanning F-Curves for their first & last frames otherwise. */
+void BKE_action_get_frame_range(const struct bAction *act, float *r_start, float *r_end)
+{
+  if (act && (act->flag & ACT_FRAME_RANGE)) {
+    *r_start = act->frame_start;
+    *r_end = act->frame_end;
+  }
+  else {
+    calc_action_range(act, r_start, r_end, false);
+  }
+
+  /* Ensure that action is at least 1 frame long (for NLA strips to have a valid length). */
+  if (*r_start >= *r_end) {
+    *r_end = *r_start + 1.0f;
+  }
+}
+
 /* Return flags indicating which transforms the given object/posechannel has
  * - if 'curves' is provided, a list of links to these curves are also returned
  */
diff --git a/source/blender/blenkernel/intern/nla.c b/source/blender/blenkernel/intern/nla.c
index 124db07298d..0666c1dfc53 100644
--- a/source/blender/blenkernel/intern/nla.c
+++ b/source/blender/blenkernel/intern/nla.c
@@ -390,6 +390,11 @@ NlaStrip *BKE_nlastrip_new(bAction *act)
    */
   strip->flag = NLASTRIP_FLAG_SELECT | NLASTRIP_FLAG_SYNC_LENGTH;
 
+  /* Disable sync for actions with a manual frame range, since it only syncs to range anyway. */
+  if (act->flag & ACT_FRAME_RANGE) {
+    strip->flag &= ~NLASTRIP_FLAG_SYNC_LENGTH;
+  }
+
   /* assign the action reference */
   strip->act = act;
   id_us_plus(&act->id);
@@ -397,7 +402,7 @@ NlaStrip *BKE_nlastrip_new(bAction *act)
   /* determine initial range
    * - strip length cannot be 0... ever...
    */
-  calc_action_range(strip->act, &strip->actstart, &strip->actend, 0);
+  BKE_action_get_frame_range(strip->act, &strip->actstart, &strip->actend);
 
   strip->start = strip->actstart;
   strip->end = (IS_EQF(strip->actstart, strip->actend)) ? (strip->actstart + 1.0f) :
@@ -1444,7 +1449,7 @@ void BKE_nlastrip_recalculate_bounds_sync_action(NlaStrip *strip)
 
   prev_actstart = strip->actstart;
 
-  calc_action_range(strip->act, &strip->actstart, &strip->actend, 0);
+  BKE_action_get_frame_range(strip->act, &strip->actstart, &strip->actend);
 
   /* Set start such that key's do not visually move, to preserve the overall animation result. */
   strip->start += (strip->actstart - prev_actstart) * strip->scale;