add rtsp reference data and instructions for creation of reference data

tests/README.md

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+# Reference Data
+
+This README explains how the reference datasets were obtained from the provided video files `vid_h264.mp4` and `vid_mpeg4_part2.mp4`.
+
+## reference/h264
+
+## reference/mpeg4_part2
+
+## reference/rtsp
+
+This reference data was obtained by streaming one of the video files with the [LIVE555 Media Server](http://www.live555.com/mediaServer/) and then reading the RTSP stream with the motion vector extractor. To reproduce the reference data, follow the steps below.
+
+### Convert input file into H.264 video elementary stream
+
+First, convert the `vid_h264.mp4` file into a H.264 video elementary stream file. To this end, run
+```
+ffmpeg -i vid_h264.mp4 -vf scale=640:360 -vcodec libx264 -f h264 vid_h264.264
+```
+in the project's root directory.
+
+The conversion is needed, because the LIVE555 Media Server cannot directly serve MP4 files. I also tried converting and serving both input videos as Matroska, which did not work well, and WebM, which did not work at all. Hence, I decided to stick with an H.264 video elementary stream.
+
+The command also scales down the input video from 720p to 360p because the default `OutPacketBuffer::maxSize` in the media server is set too low to handle the 720p video. The server logs warnings like
+```text
+MultiFramedRTPSink::afterGettingFrame1(): The input frame data was too large for our buffer size (100176).  10743 bytes of trailing data was dropped!  Correct this by increasing "OutPacketBuffer::maxSize" to at least 110743, *before* creating this 'RTPSink'.  (Current value is 100000.)
+```
+and the resulting video frame is truncated at the bottom.
+
+### Serve the video with LIVE555 Media Server
+
+Now, we serve the file `vid_h264.264` with LIVE555 Media Server. Place the file in a folder named `data`
+```
+mkdir -p data
+cp vid_h264.264 ./data/vid_h264.264
+```
+and then run a frash manylinux Docker container, in which you mount the `data` folder as a volume
+```
+docker run -it -v $(pwd)/data:/data quay.io/pypa/manylinux_2_28_x86_64 /bin/bash
+```
+In the container install and start the LIVE555 Media Server
+```
+yum install -y wget compat-openssl10
+wget -qP /usr/local/bin/ http://www.live555.com/mediaServer/linux/live555MediaServer
+chmod +x /usr/local/bin/live555MediaServer
+cd /data
+live555MediaServer &
+```
+You may have to hit `CTRL+C` now to dismiss the log of the server. The server will continue running in the background.
+
+### Consume the RTSP stream with the motion vector extractor
+
+Still in the Docker container, install the motion vector extractor
+```
+python3.12 -m pip install "motion-vector-extractor==1.1.0"
+```
+and run it to read and dump the RTSP stream to a folder named `out-reference`
+```
+/opt/python/cp312-cp312/bin/extract_mvs 'rtsp://localhost:554/vid_h264.264' --verbose --dump out-reference
+```
+
+### Preserve reference data and cleanup
+
+Finally, exist the container with
+```
+exit
+```
+Now, copy the folder `out-reference` into the `tests/reference/rtsp` folder.
+```
+cp -r data/out-reference tests/reference/rtsp
+```
+and cleanup
+```
+rm -rf data
+```