Adaptive H.264 Streaming From ArduPilot Robots
Using video cameras for live-streaming the video feed from aerial robots and other unmanned vehicles is becoming increasingly useful. Most video streaming solutions use RTP for streaming video over UDP. UDP is more efficient than TCP because it forgoes the overhead that comes with TCP's reliable delivery and congestion control mechanisms.
However, this introduces new problems when streaming video from robots. In most cases, we use the Companion Computer (CC) in Wi-Fi hotspot mode for streaming the video. Due to the limited range of 2.4GHz Wi-Fi, the Quality-of-Service (QoS) progressively gets worse when the robot moves further away from the receiving computer.
The APStreamline project aims to fix this problem by dynamically adjusting the video quality. Over UDP we can obtain estimates of QoS using RTCP packets received from the receiver. These RTCP packets provide helpful QoS information (such as RTT and packet loss) which can be used for automatically changing the bitrate and resolution of the video delivered from the sender.
The code makes use of GStreamer libraries for creating the streaming pipelines.
Some webcams such as the Logitech C920 support hardware encoding through an onboard processor, however bugs in the UVC driver has resulted in some reduced functionality. These webcams are configured to adaptively stream only in 480p through adjusting the H.264 video bitrate. Switching the resolution results in the video client closing due to the transmission of an EOS event once the resolution has changed.
All the following instructions are for installing APStreamline and APWeb on the CC. A Raspberry Pi 2/3/3B+ with the latest version of Raspian or APSync is a good choice. Intel NUC's are excellent choices as well.
Do note that the Raspberry Pi 3 and 3B+ have very low power Wi-Fi antennae which aren't great for video streaming. Using a portable Wi-Fi router like the TPLink MR3020 can dramatically improve range. Wi-Fi USB dongles working in hotspot mode can help as well.
Install the gstreamer dependencies:
sudo apt install libgstreamer-plugins-base1.0* libgstreamer1.0-dev libgstrtspserver-1.0-dev gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly python3-pip
Install meson from pip and ninja for building the code:
sudo pip3 install meson
sudo apt install ninja-build
Navigate to the cloned folder folder and run:
meson build
cd build
meson configure --prefix=$HOME/apsync/ap_streamline
sudo ninja install # installs to ~/apsync/ap_streamline for APWeb to spawn the process
./stream_server
On the Raspberry Pi, use sudo modprobe bcm2835-v4l2 to load the V4L2 driver for the Raspberry Pi camera. Add bcm2835-v4l2 to /etc/modules for automatically loading this module on boot.
The APWeb server project enables setting several flight controller parameters on the fly through the use of a Companion Computer (e.g. the Raspberry Pi). We use this APWeb server for configuring the video streams as well.
Clone the forked branch with APStreamline support here:
git clone -b video_streaming https://github.com/shortstheory/APWeb.git
cd APWeb
Install libtalloc-dev and get the MAVLink submodule:
sudo apt-get install libtalloc-dev
git submodule init
git submodule update
Build APWeb:
cd APWeb
make
./web_server -p 80
In case it fails to create the TCP socket, try using sudo ./web_server -p 80. This can clearly cause bad things to happen so be careful!
Video livestreams can be launched using RTSP. It is recommended to use RTSP for streaming video as it provides the advantages of supporting multiple cameras, conifguring the resolution on-the-fly, and recording the livestreamed video to a file.
Start the APWeb server. This will serve the configuration page for the RTSP stream server. Connect to the web server in your favourite web browser by going to the IP address of the Companion Computer.
On navigating to the new video/ page, you will be presented with a page to start the RTSP Server:
On selecting the desired interface and starting the RTSP Server, the APWeb server will spawn the Stream Server process. The stream server will search for all the V4L2 cameras available in /dev/. It will query the capabilities of all these cameras and select hardware encoding or software encoding accordingly. The list of available cameras can be refreshed by simply stopping and starting the server.
From here, the APWeb page will display the list of available RTSP streams and their mount points:
The video quality can either be automatically set based on the avaialble network bandwidth or set manually for more fine-grained control.
The APWeb page also presents an option to record the video stream to a file on the CC. For this the video stream must be opened on the client. This works with any of the manually set resolutions but does not work with Auto quality. This is because the dynamically changing resolution causes problems with the file recording pipeline. An exception to this is the UVC cameras which can record to a file in Auto mode as well.
The RTSP streams can be viewed using any RTSP player. VLC is a good choice.
For example, this can be done in VLC by going to "Media > Open Network Stream" and pasting in the RTSP Mount Point for the camera displayed in the APWeb configuration page. However, VLC introduces two seconds of latency for the jitter reduction, making it unsuitable for critical applications. To circumvent this, RTSP streams can also be viewed at lower latency by using the gst-launch command:
gst-launch-1.0 playbin uri=<RTSP-MOUNT-POINT> latency=100
As an example RTSP Mount Point looks like: rtsp://192.168.0.17:8554/cam0. Refer to the APWeb page to see the mount points given for your camera.
Launch the RTSP stream server by running:
stream_server <interface>
The list of available network interfaces can be found by running ifconfig.