[postprocessor] Fix chapters if duration is not extracted (#6037)

Authored by: bashonly

yt_dlp/postprocessor/ffmpeg.py

@@ -302,6 +302,11 @@ class FFmpegPostProcessor(PostProcessor):
             None)
         return num, len(streams)
 
+    def _fixup_chapters(self, info):
+        last_chapter = traverse_obj(info, ('chapters', -1))
+        if last_chapter and not last_chapter.get('end_time'):
+            last_chapter['end_time'] = self._get_real_video_duration(info['filepath'])
+
     def _get_real_video_duration(self, filepath, fatal=True):
         try:
             duration = float_or_none(
@@ -678,6 +683,7 @@ class FFmpegMetadataPP(FFmpegPostProcessor):
 
     @PostProcessor._restrict_to(images=False)
     def run(self, info):
+        self._fixup_chapters(info)
         filename, metadata_filename = info['filepath'], None
         files_to_delete, options = [], []
         if self._add_chapters and info.get('chapters'):
@@ -1040,6 +1046,7 @@ class FFmpegSplitChaptersPP(FFmpegPostProcessor):
 
     @PostProcessor._restrict_to(images=False)
     def run(self, info):
+        self._fixup_chapters(info)
         chapters = info.get('chapters') or []
         if not chapters:
             self.to_screen('Chapter information is unavailable')

yt_dlp/postprocessor/modify_chapters.py

@@ -23,6 +23,7 @@ class ModifyChaptersPP(FFmpegPostProcessor):
 
     @PostProcessor._restrict_to(images=False)
     def run(self, info):
+        self._fixup_chapters(info)
         # Chapters must be preserved intact when downloading multiple formats of the same video.
         chapters, sponsor_chapters = self._mark_chapters_to_remove(
             copy.deepcopy(info.get('chapters')) or [],