After much chasing, and testing, I have found this to be an efficient way of getting low latency high quality HD video out of an Aircraft. The latency is around 0.4 seconds at worst which would be OK for an FPV with an APM doing the hard work.
I will continue to search for methods to drop the latency down further, but this is a lot better than the 6-12 seconds I was getting on my first attempts.
Any comment (with useful instructions) would be appreciated.
For the wireless link, I am using two UBIQUITY ROCKET M 900 with Australian ACMA approved firmware, at the base station, I am using a tracking (yet to built the tracker...) 1.5 meter long X and Y polarised Yagi, and on the plane, two RF Design flexible strip antennas, placed at right angles to each other.
but how you do that bit is up to you.....
the critical bit is getting the Raspberry Pi's to chat to each other.
I have tried to make this as user friendly as possible... good luck.
Setting up IP video for Raspberry Pi 1080p video (FPV)
You will need 2 B model Raspberry Pi's and 1 Pi Camera. (Element 14, or RS components)
Preparing your Raspberry Pi for first boot…
Follow the instructions at http://www.raspberrypi.org/wp-content/uploads/2012/04/quick-start-guide-v2_1.pdf
Install the prepared SD card in the Pi and boot.
Setting up your Pi
Connect the Pi to your router with a network cable.
On Start-up it will resize the FAT partition and present you with a menu.
Set your language, and keyboard layout.
Select Raspbian… then click install.
After this has extracted (will take a while….) it will reboot into the configuration screen (again will take a while for this first boot.)
The important things to change here are
- Enable the camera
- In advance options…..
- Set the host name (camera, for the camera end, receiver, for the viewing end)
- Memory split, set the memory for the GPU to 256
- Enable SSH ( will come in handy later, as you may need to talk to the Pi in the air.....
Then finish and reboot.
First login
Username: pi
Password: raspberry
Setting up the required programs for video streaming
Install the dependencies by running the following in a terminal:
sudo apt-get install mplayer netcat
cd /opt/vc/src/hello_pi
make –C libs/ilclient
make –C libs/vgfont
cd /opt/vc/src/hello_pi/hello_video
make
cd ~
Now repeat this for the other Pi….
Streaming…
First set up the receiver….
Ensure the receiver is connected to your network and run
ifconfig
after you press enter, you can find your ip Address. Note this down.
Then run the following.
mkfifo buffer
nc -p 5001 -l > buffer | /opt/vc/src/hello_pi/hello_video/hello_video.bin buffer
the Pi will now wait for the feed.
On the Camera Pi
Ensure camera is connected to the Pi
Ensure Pi is connected to the network (you can confirm this with ifconfig)
(see instructions at http://www.raspberrypi.org/camera for how to connect the camera)
In the following command, replace the ip address with the one you just noted down.
raspivid -t 0 -fps 15 -o - | nc 192.168.1.85 5001
if all goes well you should be streaming 1080P video at 15fps with less than 0.5seconds of delay..
now add your wireless bridge between the two, and away you go J
This information has come from the Raspberry Pi foundation website, and other sources, tested and proven by myself..
Comments
1080p
H.264
15fps
Less than 0.4s lag via 900Mhz
Pi camera in
To
Pi HDMI out
Via Wifi 900MHz
Please all grab some Pi's and test some configurations out.
If anyone can figure it out, using a HD cam on a beaglebone black would also be of great interest at the transmitting end.
I am thinking along the same lines as Christiaan. I have a couple of 900 loco's that are just sitting around. I will try to determine how heavy it will be if I strip the chassis and set it up to use some of IBcrazy's 900 mhz circular polarized (has an external rp-sma). Bit big for a quad but might work well on a plane.
I have bought my Raspberry Pi with the camera (rev 1.3) and I have successfully streamed via UDP and RTSP (very slow) and what I wanted to say is, I wish there was more blogs like this, thank you Phillip. Now it is just to find an effective WiFi solution that is light enough (baby steps). Does anyone know of a tutorial on how to connect the APM's telemetry (not USB) to the Raspberry Pi so I can have link over TCP?
@Tommy: Most live sources will timestamp by default, and elements will keep the timestamp unless sync=off. Just use gst-inspect on your elements to see what parameters are available. And in my experience using VLC as the receiver is not ideal for low latency, and has problems when trying to receive without using buffers. gstreamer->gstreamer and latency=0 parameter for no buffering, results in less then 100ms latency on a local network (depending on the camera and capture card latency off course).
@John Arne: Do you have any idea of how to timestamp frames? :) I use Gstreamer 1.0 to send and VLC for Windows to recieve.
Some generic hints for low latency streaming under difficult conditions with signal loss aka FPV.
1. Use UDP, the stream will get data loss regardless and UDP is much more efficient then TCP
2. Timestamp frames so that you can use latency and drop-on-latency parameters to make the system drop late frames instead of trying to catch up all the time when there is not enough bandwidth because of degraded signal strength.
I also use RTP/UDP at my Pi. And i use H.264 hardware compression.
@Justin. You will never regret buying the 2 Raspi's, even if this project doesn't turn out to work well enough for FPV (I am confident it will work though).
Here is a list of 20 other projects you can use your Pi with: http://gearburn.com/2013/10/20-cool-ideas-for-your-raspberry-pi/
(sorry for being a little off-topic)
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