Change dockerfile for faster builds. Incl. ffmpeg

Dockerfile

@@ -1,7 +1,11 @@
 FROM python:3.9
 
+# TODO manually compile ffmpeg, to prevent useless deps and decrease build size
+# for that, see here: https://stackoverflow.com/questions/53944487/how-to-install-ffmpeg-in-a-docker-container
+# pin ffmpeg version to prevent issues down the road
+RUN apt-get update && apt-get -y install ffmpeg=7:4.3.*
+
 RUN mkdir /app 
-COPY /app /app
 COPY pyproject.toml /app 
 COPY poetry.lock /app 
 
@@ -11,4 +15,9 @@ RUN pip3 install poetry
 RUN poetry config virtualenvs.create false
 RUN poetry install --no-dev
 
+# copy files as late as possible, these change the most
+# forcing a rerun of all layers
+COPY /app /app
+
+
 ENTRYPOINT poetry run python webserver.py --storage /files