diff --git a/Dockerfile b/Dockerfile
index 8f50791..b646258 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,11 +1,14 @@
-FROM python:3.13-slim AS runtime
+# Alpine rather than Debian slim purely because of ffmpeg's dependencies.
+# Debian's ffmpeg depends on libavdevice, which can render to X11, Wayland and
+# OpenGL, so it drags in Mesa and with it LLVM (127 MB) and Z3 (27 MB) to
+# encode an MP3 on a headless NAS. Alpine's build brings none of that: 576 MB
+# down to 189 MB.
+FROM python:3.13-alpine AS runtime
 
 ENV PYTHONUNBUFFERED=1
 
 # ffmpeg does the encoding; the application itself has no Python dependencies.
-RUN apt-get update \
-    && apt-get install --no-install-recommends -y ffmpeg \
-    && rm -rf /var/lib/apt/lists/*
+RUN apk add --no-cache ffmpeg
 
 WORKDIR /app
 COPY pyproject.toml README.md ./