Test screen recording with ffmpeg

Dockerfile-ffmpeg-xvfb

FROM alpine:latest

# install ffmpeg and xvfb, as well as mpv
RUN apk add --no-cache ffmpeg xvfb mpv bash \
  && rm -rf /var/cache/apk/*

ENTRYPOINT ["/bin/bash"]

test.sh

# To build:
#
# docker build -t test -f Dockerfile-ffmpeg-xvfb .
#
# To start:
#
# docker run -v $(pwd):/tmp --rm -it test

Xvfb :123 -ac -nolisten tcp -screen 0 1920x1080x24 &

# replace this with a higher number if needed
targetFps=30

ffmpeg -y \
  -f lavfi -i color=black:s=1920x1080:r=$targetFps \
  -vf "drawtext=text='%{frame_num}':start_number=1:x=(w-tw)/2:y=h-(2*lh):fontcolor=black:fontsize=20:box=1:boxcolor=white:boxborderw=5" \
  -frames 100 \
  -c:v mjpeg \
  /tmp/video.nut

DISPLAY=:123 mpv --loop /tmp/video.nut &

sleep 1

ffmpeg -y \
  -progress - -nostats \
  -f x11grab -s 1920x1080 -r $targetFps -i :123 \
  -vf "drawtext=text='%{frame_num}':start_number=1:x=(w-tw)/2:y=20:fontcolor=black:fontsize=20:box=1:boxcolor=yellow:boxborderw=5" \
  -frames 100 \
  -c:v mjpeg \
  /tmp/recording.nut

kill $(jobs -p)