fixes

manim_slides/slide/base.py

@@ -405,10 +405,7 @@ def _save_slides(self, use_cache: bool = True) -> None:
 
         scene_files_folder.mkdir(parents=True, exist_ok=True)
 
-        # When rendering with -na,b (manim only)
-        # the animations not in [a,b] will be skipped,
-        # but animation before a will have a None source file.
-        files: List[Path] = list(filter(None, self._partial_movie_files))
+        files: List[Path] = self._partial_movie_files
 
         # We must filter slides that end before the animation offset
         if offset := self._start_at_animation_number:

manim_slides/slide/manim.py

@@ -41,7 +41,10 @@ def _resolution(self) -> Tuple[int, int]:
 
     @property
     def _partial_movie_files(self) -> List[Path]:
-        return [Path(file) for file in self.renderer.file_writer.partial_movie_files]
+        # When rendering with -na,b (manim only)
+        # the animations not in [a,b] will be skipped,
+        # but animation before a will have a None source file.
+        return [Path(file) for file in self.renderer.file_writer.partial_movie_files if file is not None]
 
     @property
     def _show_progress_bar(self) -> bool:

manim_slides/utils.py

@@ -45,6 +45,8 @@ def concatenate_video_files(ffmpeg_bin: Path, files: List[Path], dest: Path) ->
 
 def merge_basenames(files: List[Path]) -> Path:
     """Merge multiple filenames by concatenating basenames."""
+    if len(files) == 0:
+        raise ValueError("Cannot merge an empty list of files!")
 
     dirname: Path = files[0].parent
     ext = files[0].suffix