[ThumbnailsConvertor] Fix conversion after fixup_webp

Closes #4565

diff --git a/yt_dlp/postprocessor/ffmpeg.py b/yt_dlp/postprocessor/ffmpeg.py
index 6a0a8220ba777f5cfcbfcddf8659bcdeefa7e1ab..a1f367ae42625c4867942ee76ed194c9533d9203 100644 (file)
--- a/yt_dlp/postprocessor/ffmpeg.py
+++ b/yt_dlp/postprocessor/ffmpeg.py
@@ -1105,6 +1105,7 @@ def run(self, info):
                 continue
             has_thumbnail = True
             self.fixup_webp(info, idx)
+            original_thumbnail = thumbnail_dict['filepath']  # Path can change during fixup
             thumbnail_ext = os.path.splitext(original_thumbnail)[1][1:].lower()
             if thumbnail_ext == 'jpeg':
                 thumbnail_ext = 'jpg'