diff --git a/Dockerfile b/Dockerfile
index 11199d614..b886fb683 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,7 @@
 # Handles compiling and package installation
-FROM ubuntu:18.04 AS compile-image
+FROM ubuntu:20.04 AS compile-image
 # Install build dependencies
+ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends \
         python3 python3-pip \
         # Required for local pip install
@@ -9,7 +10,11 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         python3-venv \
         # Required to build RLE module and dbus-python (GUI)
         build-essential python3-dev \
-        libdbus-1-dev libdbus-glib-1-dev
+        libdbus-1-dev libdbus-glib-1-dev \
+        # Required to build PyAV (pyrdp-convert to MP4)
+        libavformat-dev libavcodec-dev libavdevice-dev \
+        libavutil-dev libswscale-dev libswresample-dev libavfilter-dev
+
 
 RUN python3 -m venv /opt/venv
 # Make sure we use the virtualenv:
@@ -31,9 +36,10 @@ RUN cd /pyrdp \
 
 
 # Handles runtime only (minimize size for distribution)
-FROM ubuntu:18.04 AS docker-image
+FROM ubuntu:20.04 AS docker-image
 
 # Install runtime dependencies except pre-built venv
+ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends python3 \
         # To generate certificates
         openssl \
@@ -42,6 +48,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends python3 \
         # GUI and notifications stuff
         libgl1-mesa-glx \
         notify-osd dbus-x11 libxkbcommon-x11-0 \
+        # Runtime requirement for PyAV (pyrdp-convert to MP4)
+        libavcodec58 libavdevice58 \
         # Runtime requirement by progressbar (required by pyrdp-convert)
         python3-distutils \
         && rm -rf /var/lib/apt/lists/*
diff --git a/Dockerfile.slim b/Dockerfile.slim
index 8097370c4..7a16e5074 100644
--- a/Dockerfile.slim
+++ b/Dockerfile.slim
@@ -3,8 +3,9 @@
 # and notification system integration.
 #
 # Handles compiling and package installation
-FROM ubuntu:18.04 AS compile-image
+FROM ubuntu:20.04 AS compile-image
 # Install build dependencies
+ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends \
         python3 python3-pip \
         # Required for local pip install
@@ -32,9 +33,10 @@ RUN cd /pyrdp \
 
 
 # Handles runtime only (minimize size for distribution)
-FROM ubuntu:18.04 AS docker-image
+FROM ubuntu:20.04 AS docker-image
 
 # Install runtime dependencies except pre-built venv
+ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends python3 \
         # To generate certificates
         openssl \
diff --git a/docs/devel.adoc b/docs/devel.adoc
index 0fac9d6b3..8b5400c79 100644
--- a/docs/devel.adoc
+++ b/docs/devel.adoc
@@ -4,6 +4,26 @@
 
 NOTE: This is a work in progress
 
+.Update dependencies
+
+For developement and normal installation we rely on `setup.py` with loose dependencies.
+For docker images we rely on `requirements.txt` and `requirements-slim.txt` with strict dependencies.
+It is important to keep both approaches in sync and to peridiocally update the requirements files (like before releases).
+See https://github.com/GoSecure/pyrdp/pull/219[the PR where we improved our use of the docker cache] for the reasoning behind this approach.
+
+In a clean tree, on master:
+
+* install and load the venv
+* do a `pip freeze > requirements.txt`
+* manually inspect updated dependencies
+* copy over to `requirements-slim.txt` those that make sense (don't add av, PySide2, etc.)
+
+If you are unsure about which to keep and which to discard between `requirements.txt` and `requirements-slim.txt`, just look at a diff of a previous version.
+
+.Test
+
+docker images (latest, slim), on linux, on Windows
+
 .Update the changelog
 * You can generate author list with where `<tag>` is replaced with previous release's tag:
 +
diff --git a/requirements.txt b/requirements.txt
index 4e88cb76f..2b6999744 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,7 @@
 appdirs==1.4.3
 attrs==19.3.0
 Automat==20.2.0
+av==8.0.2
 cffi==1.14.0
 constantly==15.1.0
 cryptography==2.9
@@ -10,7 +11,9 @@ idna==2.9
 incremental==17.5.0
 names==0.3.0
 notify2==0.3.1
-progressbar2==3.51.3
+Pillow==7.2.0
+pillowcase==2.0.0
+progressbar2==3.51.4
 pyasn1==0.4.8
 pyasn1-modules==0.2.8
 pycparser==2.20
@@ -18,6 +21,7 @@ pycryptodome==3.9.7
 PyHamcrest==2.0.2
 pyOpenSSL==19.1.0
 PySide2==5.14.2
+python-utils==2.4.0
 pytz==2019.3
 rsa==4.0
 scapy==2.4.3