diff --git a/movmaker.py b/movmaker.py
index 8d5c863..5ae8975 100755
--- a/movmaker.py
+++ b/movmaker.py
@@ -55,6 +55,15 @@ LOG_PATH: Path | None = None
 
 
 def tool_path(local_path: Path, fallback: str) -> str:
+    """Return the preferred executable path for ffmpeg/ffprobe style tools.
+
+    Args:
+        local_path: Path to a bundled copy shipped with movmaker.
+        fallback: Name of the system executable to call when the bundled copy is missing.
+
+    Returns:
+        The fully-qualified path to execute.
+    """
     return str(local_path) if local_path.exists() else fallback
 
 
@@ -76,12 +85,14 @@ class MediaItem:
 
 
 def log_message(message: str) -> None:
+    """Append a diagnostic line to the current render log if it is enabled."""
     if LOG_PATH:
         with LOG_PATH.open("a", encoding="utf-8") as log:
             log.write(message.rstrip() + "\n")
 
 
 def ffmpeg_progress_cmd(cmd: list[str], progress: bool) -> list[str]:
+    """Inject ffmpeg-friendly progress flags when progress monitoring is requested."""
     if not cmd or Path(cmd[0]).name != "ffmpeg":
         return cmd
     out = [cmd[0], "-hide_banner", "-nostats"]
@@ -104,6 +115,12 @@ def format_bytes(value: int) -> str:
 
 
 def run(cmd: list[str], progress_duration: float | None = None) -> None:
+    """Execute a subprocess while streaming progress and teeing output to the log.
+
+    Args:
+        cmd: argv array ready for subprocess.run.
+        progress_duration: Expected output duration in seconds used to estimate progress; omit for instant commands.
+    """
     progress = progress_duration is not None and progress_duration > 0 and Path(cmd[0]).name == "ffmpeg"
     run_cmd = ffmpeg_progress_cmd(cmd, progress)
     log_message("+ " + shlex.join(run_cmd))
@@ -483,6 +500,7 @@ def media_date(path: Path) -> datetime:
 
 
 def ascii_safe(value: str) -> str:
+    """Return a human-readable ASCII approximation of Scandinavian/Slavic letters."""
     replacements = {
         # Danish letters
         "æ": "ae", "Æ": "Ae",
@@ -505,6 +523,7 @@ def ascii_safe(value: str) -> str:
 
 
 def slugify(value: str) -> str:
+    """Convert an arbitrary string into a filesystem-safe slug."""
     value = ascii_safe(value)
     value = value.strip().lower()
     value = re.sub(r"[^a-z0-9]+", "_", value)
@@ -525,6 +544,7 @@ def display_date(dt: datetime) -> str:
 
 
 def prepare_clip_stamps(media: list[MediaItem], data: MovieData) -> list[str]:
+    """Build per-clip stamp strings containing title/date/place metadata."""
     geocode_cache: dict[tuple[float, float], str | None] = {}
     stamps: list[str] = []
     for item in media:
@@ -566,6 +586,7 @@ def natural_key(path: Path) -> list[object]:
 
 
 def scan_input(input_dir: Path, image_duration: float) -> tuple[list[MediaItem], list[Path], MovieData]:
+    """Detect media/audio/data files inside the input directory and build metadata."""
     if not input_dir.is_dir():
         raise SystemExit(f"Input directory does not exist: {input_dir}")
 
@@ -678,6 +699,15 @@ def drawtext_escape(text: str) -> str:
 
 
 def render_intro_logo_frame(logo: Path, out: Path, width: int, height: int, alpha: float) -> None:
+    """Build a single black frame with the intro logo centered and scaled.
+
+    Args:
+        logo: Source PNG to overlay.
+        out: Destination PNG path for the composed frame.
+        width: Target video width.
+        height: Target video height.
+        alpha: Desired opacity between 0 and 1.
+    """
     if width <= 0 or height <= 0:
         raise ValueError("intro logo frame must have positive width/height")
     alpha = min(1.0, max(0.0, alpha))
@@ -703,6 +733,7 @@ def render_intro_logo_frame(logo: Path, out: Path, width: int, height: int, alph
 
 
 def normalize_clip(item: MediaItem, out: Path, width: int, height: int, fps: int, preset: str, crf: int) -> None:
+    """Transcode one media item into a padded, FPS-normalized H.264 clip."""
     vf = (
         f"scale={width}:{height}:force_original_aspect_ratio=decrease,"
         f"pad={width}:{height}:(ow-iw)/2:(oh-ih)/2:black,"
@@ -773,6 +804,7 @@ def load_jamendo_client_id() -> str | None:
 
 
 def download_jamendo_music(genre: str, out_dir: Path) -> Path | None:
+    """Download a random Jamendo track matching the requested genre."""
     client_id = load_jamendo_client_id()
     if not client_id:
         console("No audio files found and no Jamendo client ID configured; continuing without music.")
@@ -843,6 +875,7 @@ def download_jamendo_music(genre: str, out_dir: Path) -> Path | None:
 
 
 def concat_or_mix_audio(audio_files: list[Path], out: Path) -> Path | None:
+    """Concatenate or mix multiple audio tracks into one temp file."""
     if not audio_files:
         return None
     if len(audio_files) == 1:
@@ -885,6 +918,7 @@ def build_video(
     intro_visible_lead: float = 0.0,
     skip_video_fade_out: bool = False,
 ) -> None:
+    """Assemble normalized clips, overlays, and audio into the final MP4."""
     output.parent.mkdir(parents=True, exist_ok=True)
 
     text_file_count = 0
@@ -1144,6 +1178,7 @@ def build_video(
 
 
 def main(argv: list[str] | None = None) -> int:
+    """CLI entry point for movmaker."""
     parser = argparse.ArgumentParser(description="Make a video from a flat folder of images/videos/audio.")
     parser.add_argument("input", type=Path, help="flat input directory")
     parser.add_argument("--out-dir", type=Path, default=Path("."), help="directory for auto-named output videos")