From e9c9f19c26c3a361c4fa17947b6b5d860e516c2c Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Tue, 4 Jun 2024 18:46:35 +1000
Subject: [PATCH] Do not use first frame duration for other frames when saving

---
 Tests/test_file_apng.py   | 15 +++++++++++++--
 src/PIL/PngImagePlugin.py | 13 ++++++-------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/Tests/test_file_apng.py b/Tests/test_file_apng.py
index 1b393a3ff5d..e95850212a5 100644
--- a/Tests/test_file_apng.py
+++ b/Tests/test_file_apng.py
@@ -706,10 +706,21 @@ def test_different_modes_in_later_frames(
         assert reloaded.mode == mode
 
 
-def test_apng_repeated_seeks_give_correct_info() -> None:
+def test_different_durations(tmp_path: Path) -> None:
+    test_file = str(tmp_path / "temp.png")
+
     with Image.open("Tests/images/apng/different_durations.png") as im:
-        for i in range(3):
+        for _ in range(3):
             im.seek(0)
             assert im.info["duration"] == 4000
+
             im.seek(1)
             assert im.info["duration"] == 1000
+
+        im.save(test_file, save_all=True)
+
+    with Image.open(test_file) as reloaded:
+        assert reloaded.info["duration"] == 4000
+
+        reloaded.seek(1)
+        assert reloaded.info["duration"] == 1000
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 0d5751962c0..dde45e587e1 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -1105,7 +1105,7 @@ def write(self, data: bytes) -> None:
 
 
 def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images):
-    duration = im.encoderinfo.get("duration", im.info.get("duration", 0))
+    duration = im.encoderinfo.get("duration")
     loop = im.encoderinfo.get("loop", im.info.get("loop", 0))
     disposal = im.encoderinfo.get("disposal", im.info.get("disposal", Disposal.OP_NONE))
     blend = im.encoderinfo.get("blend", im.info.get("blend", Blend.OP_SOURCE))
@@ -1126,6 +1126,8 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
             encoderinfo = im.encoderinfo.copy()
             if isinstance(duration, (list, tuple)):
                 encoderinfo["duration"] = duration[frame_count]
+            elif duration is None and "duration" in im_frame.info:
+                encoderinfo["duration"] = im_frame.info["duration"]
             if isinstance(disposal, (list, tuple)):
                 encoderinfo["disposal"] = disposal[frame_count]
             if isinstance(blend, (list, tuple)):
@@ -1160,15 +1162,12 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
                     not bbox
                     and prev_disposal == encoderinfo.get("disposal")
                     and prev_blend == encoderinfo.get("blend")
+                    and "duration" in encoderinfo
                 ):
-                    previous["encoderinfo"]["duration"] += encoderinfo.get(
-                        "duration", duration
-                    )
+                    previous["encoderinfo"]["duration"] += encoderinfo["duration"]
                     continue
             else:
                 bbox = None
-            if "duration" not in encoderinfo:
-                encoderinfo["duration"] = duration
             im_frames.append({"im": im_frame, "bbox": bbox, "encoderinfo": encoderinfo})
 
     if len(im_frames) == 1 and not default_image:
@@ -1198,7 +1197,7 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
             im_frame = im_frame.crop(bbox)
         size = im_frame.size
         encoderinfo = frame_data["encoderinfo"]
-        frame_duration = int(round(encoderinfo["duration"]))
+        frame_duration = int(round(encoderinfo.get("duration", 0)))
         frame_disposal = encoderinfo.get("disposal", disposal)
         frame_blend = encoderinfo.get("blend", blend)
         # frame control