SLP (StereoPi Livestream Playground) Raspbian Image

Image specific

This SLP (StereoPi Livestream Playground) image was used for all livestream experiments mentioned on our crowdfunding page https://www.crowdsupply.com/virt2real/stereopi, and have some additional features. It is not comfortable for using with monitor, keyboard and mouse. We do it in consumer-like way for save our time. It has administration panel (like WiFi routers), and also accessible via SSH. As this image is compatible with both StereoPi and classic Raspberry Pi, let us use “Pi” name in this article. And last notice: by default single-camera mode is enabled for classic Raspberry Pi.

Please remember it is Beta only. If you find some bugs - do not be angry, please let us know here on raspberry Pi forum: https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=216940

Partition structure

Classic Raspbian have two partitions: BOOT and a Linux filesystem. Our image has both of them (using 4Gb on MicroSD), and also have 3rd partition in Fat32. It is used for recording captured video. So after recording a video you can insert MicroSD to your computer and see all your records, like with your car dashcam.

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How to prepare MicroSD card with SLP

1. Prepare MicroSD card 16 Gb or higher capacity 2. Download image file and unzip it on your computer. 3. Write image to MicroSD. As a Pi user you might know, that it does not mean “copy-paste” image file, but need special image writing software. Under Windows we prefer to use Win32DiskImager (https://sourceforge.net/projects/win32diskimager/). 4. Do not remove MicroSD right after this procedure, as you might want to set up access to your WiFi hot spot. You can do it right after preparing image.

Tip1: Not all MicroSD marked as 16Gb have exact the same size. Win32DiskImager may warn you that your MicroSD is too small, but you have option to “continue record”. For this case we leave several hundreds of unused space at the end of MicroSD, so image will not be broken on such a cards.

Tip 2 for advanced users: Main system use only 4 Gb on MicroSD, and other ~12 Gb is used for video records. If you have only 8 Gb card, you may record our SLP image too with Win32DiskImager. But after that you need to manually fix broken Fat32 partition (create it again and format).

Network configuration

Ethernet access

If you connect Pi by Ethernet to your router, you do not need to configure it. IP address will be obtained automatically by DHCP.

WiFi access

If you did not removed prepared MicroSD from your computer, you should now go to “BOOT” disk and find “stereopi.cfg” file. Open it and write your WiFi access point name and password in this rows: {}{}{} {}{}{} If you use Raspberry Pi WITHOUT built-in WiFi or StereoPi, please do not forget co connect WiFi dongle to your device before power on. Now your Pi will automatically connect to your router after boot. If it is does not work – please check twice AP name and password. Also system might not like SSID name with spaces in it.

Trick

If you enable WiFi access point on your phone, Pi will access Internet over it. That is you can both livestream to YouTube and access admin panel. So you can livestream to YouTube using your phone and powerbank to power on your Pi.

How to find StereoPi in your network?

We use autodiscovery feature in our SLP image. So here are some approaches how to connect StereoPi using it.

Connecting to SLP with autodiscovery feature

We suggest your Pi and computer/phone/tablet connected to the same router, and your network has no difficult topology. 1. Open a browser and type: http://stereopi.local Admin panel will appear. In some networks it works immediately, but in other networks it might takt some time to find and open panel (10-20 seconds). <><>СКРИНШОТ<><>

2. Open our Android application. It will automatically find your Pi, connect to it and starts playing livestream video. If you tap on the screen you will see prompt with IP address. If you tap on it, then browser will be opened with admin panel. <><>СКРИНШОТ<><>

Connecting to SLP with other methods

1. You can use software for network scan to find IP address. For Windows you can use Advanced IP Scanner (http://www.advanced-ip-scanner.com). <><>СКРИНШОТ<><>

For Mac it is LanScan (https://itunes.apple.com/us/app/lanscan/id472226235?mt=12). <><>СКРИНШОТ<><> 2. You can go to your router admin panel and look for IP addresses in a list of connected devices. 3. After you’ve found IP address, type it in your browser.

Android application

This simple application automatically connects to Pi with SLP image, requests video livestream and show it. If you use StereoPi and “3D” mode enabled in Admin panel – you can enjoy 3D video by putting your phone to google cardboard-like device. If you use classic Pi you can see video livestream from your camera. We use either this ColorCross viewer or compact solution:

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Tap on the screen shows you prompt with current IP address of Pi. Click on this prompt will open browser with admin panel. You can also use this application on Oculus Go as we did. Put your Oculus Go in developer mode and upload application. At this moment there are no joystick support for Oculus, and we plan to add it later.

Compatibility

Application was tested on Android 7.1.1, 7.1.2 and 8.0 It is compiled for Anndoids >=5, but was not tested with 5 and 6 versions.

Performance notice

With old Android phones (5 years or more) you may obtain high latency of your video (delay up to 0,3-0,5 seconds). With newer models video latency is near 0,1 seconds.

HDMI stereoscopic preview (RC FPV usage)

Right after start Pi will push image from camera to HDMI output. For 3D view on HDMI we used some trick. By default Raspbian turn HDMI in 3D mode if it needs to show 3D image, for devices like 3D TV. So on classic monitor you will see image from one camera and a part of image from second camera. We have modified raspivid and manually turned HDMI in non-3d mode. So if you’re RC modelist and want to livestream 3D from StereoPi using your FPV link with HDMI capture – just connect StereoPi to it. In the future we will discuss this option with Raspbian support team to find easier way to trigger this 3D/non-3D HDMI mode.

How to look at your 3D livestream video

Android phone and local WiFi stream Android phone and YouTube Oculus Go and local WiFi stream Oculus Go and YuTube

SLP admin panel options

Recording

If you turn on this feature, Pi will record all video to MicroSD card.

Max rec duration

Recorded video will be cut on pieces with chosen length. Why do you need it? Answer is simple. We capture “raw” h264 stream from camera. If we will record it directly, you will feel some problems while viewing it in your video player. For example, scroll may not work etc. So we need to convert it to MP4 for comfort use. Our SLP do it on-the-go. But to do it correctly our utility need to add some information to the file. If you turn off your Pi while this process you may lose your last record, but all previous records remain safe. What time to choose? For short on-table experiments it is better to set minimal time (30 seconds). For real-life experiments it is better to set 5-10 minutes.

Stream UDP

Section for advanced users. You may put IP addresses and ports of devices you want livestream to. You may use several comma-separated values in “UDP clients” field, like this: 192.168.1.10:3000,192.168.1.20:4000 To capture this stream you may use your own application or gstreamer (see Advanced User’s Section).

UDP clients

Field for UDP clients (for Stream UDP option).

Broadcast

This option enables broadcast livestream to all clients in your network.

Audio enabled

If you connect USB sound card with Microphone, or USB microphone, system will try to stream video with sound.

RTMP URL (YouTube etc.)

If you put RTMP string here, Pi will send livestream to it. For livestream to YouTube you need to copy livestream link from your YouTube studio and put it in this field. Our link looks like this: rtmp://a.rtmp.youtube.com/live2/9k1d-2ue3-xxxx-xxxx

Trick:

YouTube does not allow livestream without sound. So if SLP has not detected USB soundcard and Microphone, it adds fake silence sound to this stream, and it works. If you have USB soundcard and mic, you will hear sound on YouTube.

Tip:

If you have no experience on YouTube livestream, you should know that YouTube adds time-buffer up to 30 seconds for your video. That is you will not see your video immediately, and when you see it you can find some delay. It is not a bug, it is a feature. It helps viewers to obtain smooth and high-quality video.

Video mode

Choose 3D if you have StereoPi or another Pi-based solution with two cameras connected. Choose 2D if you have classic Raspberry Pi. If you use this option with StereoPi, only one camera will be used for video capture.

Decimation

This option scale each taken image horizontally to 50% of its original width. This feature is useful for FPV and Depth Map, as you save full FOV (field of view) of your camera. For other implementations you may uncheck this option. In this case FOV will be cropped, but you have normal side ratio of your video. For our Oculus experiment we unchecked this option. In fact this option adds “-dec” parameter to raspivid.

Upside/Down

Rotate image on 180 degree. With 1 camera it is simple. With 2 cameras we do flip and also swap left/right images. Otherwise your left and right images appear on a wrong place, and your brain will be stuck on trying to build 3D image from this.

Video resolution

Resolution of video captured.

FPS

Frames Per Second settings for video. Please notice, that if you choose too high FPS for high resolution you may obtain capture problems. For 1280x720 with ONE camera you may use 48 FPS. For 1280x720 and 3D use 42 FPS. You can experiment with these settings to fit your needs. We want to notice that highest FPS is critical for at least two scopes. First one is livestream to VR helmets like Oculus, as perception comfort depend on this. The second one is RC FPV, as higher FPS decrease video latency.

Bitrate

Number of megabits used for 1 second of video after compression, in megabits (not megabytes). This settings affects on H264 encoder of your Pi. The higher bitrate, the better video quality you have, and the more bandwidth connection required for livestream. For livestream we recommend to use 2-3 Mbit at HD or FullHD resolution. For 640x480 even 1 Mbit is Ok. Higher bitrates are useful for recording video on MicroSD without livestream. Please notice you need a high-speed MicroSD to record at high bitrates.

White balance

Changes white balance mode. In this option we implemented options available for Raspberry Pi Camera (https://www.raspberrypi.org/documentation/raspbian/applications/camera.md)

Exposure

Changes exposure mode. In this option we implemented options available for Raspberry Pi Camera (https://www.raspberrypi.org/documentation/raspbian/applications/camera.md)

Contrast

Changes contrast mode. In this option we implemented options available for Raspberry Pi Camera (https://www.raspberrypi.org/documentation/raspbian/applications/camera.md)

Sharpness

Changes sharpness mode. Notice: looks like this feature implementation have a bug in Raspbian, as it is implemented to only one camera in stereoscopic mode. In this option we implemented options available for Raspberry Pi Camera (https://www.raspberrypi.org/documentation/raspbian/applications/camera.md)

Digital gain

Changes digital gain mode. In this option we implemented options available for Raspberry Pi Camera (https://www.raspberrypi.org/documentation/raspbian/applications/camera.md)

Wifi SSID

Name of you WiFi access point Can be adjusted here or in “stereopi.cgf” file in a BOOT partition

WiFi password

Password for your WiFi.

Updating software

If we have update, we create a file named stereopi.tar.gz You can put it in “BOOT” part of MicroSD. After start SLP will automatically find it and implement.

Advanced users’ section

SSH access

You might want to look inside. When you know IP address of your Pi you can access it by SSH. User credentials are the same as for default user: login: pi password: raspberry

SLP structure details you should know

1. We prepared this image for aggressive usage, that’s why we want to save filesystem in a case of occasional poweroffs. So by default filesystem is read-only and you cannot change any file. To unlock it type: sudo mount -o rw,remount /

2. MC already installed, you may use it.

3. Our streaming scripts are here: /opt/stereopi To stop script run ./stop.sh To run them again run: ./run.sh

4. Automount Win32 partition for video records is here:

5. Most scripts have auto-restart feature

6. “chunker” utility We have a lot of projects when we capture video from one source and need to use it in several ways at the same time (like livestream, record and use for Computer Vision). So we need to send it to several applications at the same time. We use network approach with this, and subsystems of our projects talk with each other over network infrastructure with 127.0.0.1 and different ports. This approach gives us flexibility and we can easily forward video stream to internal subsystem or to external IP address. For example, if you decide to move your OpenCV part from Pi to nearby NVidia Jetson, you just aim livestream from internal IP and port to Jetson’s one. So “in the root” of this system we have special “chunker” utility. It cuts video stream on pieces to fit network bandwidth with maximum efficiency, and try to adapt to maximum MTU available. At this moment this utility is overloaded with a lot of features for our custom projects. We will exclude all unneeded features and open source it after polishing.

Receive livestream on Windows

You need to have gstreamer 1.x installed. If you already have it, run this script: gst-launch-1.0 -v udpsrc port=3000 buffer-size=300000 ! h264parse ! avdec_h264 ! fpsdisplaysink sync=false

Receive livestream on iOS devices

For iOS we used gstreamer-based application Fishing FanCam application (https://github.com/rodizio1/EZ-WifiBroadcast/wiki/GCS-~-FishingFanCam). But looks like it is not supported now. We plan to do our own application for this, but it might take a lot of time. We will be pleased If you can suggest other gstreamer-based iOS applications or help us with making simple application like our Android one.