diff --git a/yt_dlp/postprocessor/ffmpeg.py b/yt_dlp/postprocessor/ffmpeg.py
index 0535afbbc..bc320f7ad 100644
--- a/yt_dlp/postprocessor/ffmpeg.py
+++ b/yt_dlp/postprocessor/ffmpeg.py
@@ -597,7 +597,7 @@ def __init__(self, downloader=None, already_have_subtitle=False):
 
     @PostProcessor._restrict_to(images=False)
     def run(self, info):
-        filename, ext = info['filepath'], info['ext']
+        ext = info['ext']
         if ext not in self.SUPPORTED_EXTS:
             self.to_screen(f'Subtitles can only be embedded in {", ".join(self.SUPPORTED_EXTS)} files')
             return [], info
@@ -607,6 +607,8 @@ def run(self, info):
             self.to_screen('There aren\'t any subtitles to embed')
             return [], info
 
+        filename = info['filepath']
+
         # Disabled temporarily. There needs to be a way to override this
         # in case of duration actually mismatching in extractor
         # See: https://github.com/yt-dlp/yt-dlp/issues/1870, https://github.com/yt-dlp/yt-dlp/issues/1385
@@ -677,9 +679,9 @@ def _embed_lyrics(self, subtitles, filename, ext):
         self.to_screen(f'Embedding lyrics in "{filename}"')
         if len(subtitles) > 1:
             self.report_warning(
-                f'Your media player may be unable to display multiple subtitles in {ext}')
+                f'Your media player may be unable to display multiple subtitles in {ext}', only_once=True)
 
-        for lang, sub in subtitles.items():
+        for sub in subtitles.values():
             if not sub.get('data'):
                 with open(sub['filepath'], encoding='utf-8') as f:
                     sub['data'] = f.read()
diff --git a/yt_dlp/utils/subtitles.py b/yt_dlp/utils/subtitles.py
index 08040b202..663e3e6e9 100644
--- a/yt_dlp/utils/subtitles.py
+++ b/yt_dlp/utils/subtitles.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import re
 from dataclasses import dataclass
 
@@ -14,7 +16,7 @@ class Metadata:
 class Subtitle:
     text: str
     start: Seconds
-    end: Seconds = None
+    end: Seconds | None = None
 
 
 def parse_lrc(text):