Fix typing errors in ffprobe functions.

src/tscut/tools/ffprobe.py

@@ -85,6 +85,10 @@ def get_frame_rate(ffprobe_path:str, input_file: IO[bytes]) -> float|None:
         logger.error("ffprobe returns an error code: %d", ffprobe.returncode)
         return None
 
+    if max_ts is None or min_ts is None:
+        logger.error("Impossible to determine maximum or minimum timestamps.")
+        return None
+
     frame_rate1 = nb_frames1/(max_ts-min_ts)
     frame_rate2 = nb_frames2 / mean_duration
 
@@ -102,7 +106,7 @@ def get_frame_rate(ffprobe_path:str, input_file: IO[bytes]) -> float|None:
     return frame_rate2
 
 @typechecked
-def get_subtitles_tracks(ffprobe_path:str, mkv_path: str) -> dict[str,str]|None:
+def get_subtitles_tracks(ffprobe_path:str, mkv_path: str) -> dict[str,list[str]]|None:
     tracks={}
 
     with Popen([ffprobe_path, '-loglevel', 'quiet', '-select_streams', 's', '-show_entries',
@@ -114,7 +118,7 @@ def get_subtitles_tracks(ffprobe_path:str, mkv_path: str) -> dict[str,str]|None:
             for stream in out['streams']:
                 index = stream['index']
                 codec = stream['codec']
-                lang = stream['tags']['language']
+                lang:str = stream['tags']['language']
                 if codec == 'dvd_subtitle':
                     if lang not in tracks:
                         tracks[lang] = [index]