OBS - Open Broadcast Studio

Open Broadcast Studio is a free and open source software for video recording and live streaming. Used with a separate software video encoder, such as F1EJP's FreeStreamCoder, it can give a semi-professional look to the content sent to a Portsdown DATV transmitter. You can create scenes made up of multiple sources including window captures, images, text, browser windows, webcams, capture cards and more. This configuration produces an HD 1280 x 720 25 fps output configured for a H264 encoded 333kS/s FEC 3/4 transmission.

Hardware

You will need a capable PC. It should have an Intel i5-10500 processor or better, 16GB RAM, an SSD and ideally an nVidia graphics card that supports NVENC video encoding. GTX1050, GTX1070, GTX1660, RTX A2000, RTX3050 etc. or better are suitable models. It's also possible to use the QuickSync video encoder built into the Intel processor mentioned above or later versions with acceptable results.

Your Portsdown and PC must be connected to the same Ethernet network. Usually, you would add a cable from your Portsdown to a spare LAN port on the Internet router. Alternatively, use a small ethernet switch in the shack with a feed back to the router. Don't be tempted to use WiFi for either the Portsdown or the PC; the results will be disapointing.

The Portsdown 4 with either a Pluto or Lime SDR and the Raspberry Pi 3 based Portsdown 2020 with a BATC Filter/Modulator board can be used.

Software

Your PC should be running Microsoft Windows 10 or 11 and be updated to the 22H2 release. If using an nVidia graphics card it is essential to use the latest drivers. See the nVidia website.

Download OBS v27.2.4. It's not the latest version, but can be found (amongst others) from this archive: https:// www.filehorse.com/download-obs- ... /download/ and install it. Later versions will not work with the Virtual Camera below, so ignore any requests to upgrade to a newer version.

Download the Virtual Camera v2.05 plugin from here: https://obsproject.com/forum/resources/obs-virtualcam.949/download Open the file and the installer should find the OBS installation and place the files in the right place.

Download FreeStreamEncoder from here: http://www.vivadatv.org/viewtopic.php?f=78&t=1007 Create a folder in the root of your C: drive named F1EJP (C:\F1EJP). Copy the downloaded file to the new folder and extract the content of the zip archive to this folder.

FreeStreamCoder configuration

Once you have set the Portsdown up and connected to the network, get its IP address from the Info button at the bottom of the M2 menu. Typically it will be 192.168.1.xxx where xxx is a number from 2 to 253. Run the FreeStreamCoder and select the middle tab. On FreeStreamEncoder, select the Configuration tab. Use the Input drop down menu to select OBS + VirtualCam.

Enter the Porstdown's IP address in the Output IP Address boxes and set the port to 10000. From the Encoder drop down menu select the appropriate entry depending on what hardware accelerated encoding is available. Leave the FPS setting at 25. Audio sample rate should be 48000. Audio sync can be adjusted later.

Now select the DVB Tables tab. Enter your callsign and optionally the location in the top boxes. The rest can be left as default.

Select the MPEG Transport Stream tab. Set DVB to DVB-S2, Symbol Rate 333, FEC to 3/4, FEC frame to 64800, Codec to H264, Image size 1280 x 720, FPS to 25, Audio codec to AAC and Audi AAC kb/s to 64. Take note if you are using a BATC Filter/Modulator board, the DVB setting must be DVB-S. DVB-S2 is not supported. That completes the set up of FreeStreamCoder.

OBS configuration

Open OBS. By default it opens with a single screen. To get a preview and program screen select the Studio Mode button in the Controls menu.

In the Controls menu select Settings and then Video on the left-hand side of the pop-up window. Set the top two resolution options to 1280 x 720. Lanczos gives the best Downscale filter results but you can play with this setting if the CPU loading is too high.

Now select the Audio settings menu. Change the default Global Audio Devices Mic/Auxilliary to a valid hardware device. This might be the integrated microphone of a C920 camera, if plugged in, for example. Sample Rate should be set to 48kHz and Channels to Stereo.

Next select the Tools menu from above the Preview screen. Click the VirtualCam button and then click the Start button in the window that appears. Also select the AutoStart check box and leave everything else as default. Close the window.

Getting started with OBS

This section is not intended to be an in-depth treatise on the use of OBS, but it should give enough detail to get a test card sent to the Portsdown. The test card image can be any a BMP, PNG or JPEG file of 1280 x 720 pixels resolution and should be placed in a folder in the C: drive root of the Windows PC. In the Scenes section click on the + button and with the Create New source button selected enter a suitable name for the test card in the pop-up dialogue. Click OK and with the new scene highlighted click on the + in the sources section.

In the pop-up window, select image and then in the Create/Select window name the new source; note that this name must be different from the scene name. Now click OK and the properties page appears for the new scene. Use the browse button to bring up a File Explorer window to navigate to the location where the test card image file was stored. Select it and click OK. Click OK.

The test card image will appear in the preview screen. If it does not fill the screen, right mouse click the image and then select Transform from the pop-up menu and then from the next pop-up menu choose Fit to screen. The image will then fill the preview screen. To keep these settings, click on the lock symbol at the right-hand end of the highlighted source button in the sources section. Now click the Transition button between the two screens and the image will transfer to the Program screen.

Testing

Set the Portsdown to IPTS Monitor; the button can be found in menu M2. Click the start button in FreeStreamCoder. Now the playback in the Program screen will appear on the Portsdown's screen delayed by around 3 seconds if all is well.

Using the system

Set the Portsdown to 333kS/s symbol rate, FEC 3/4, DVB-S2 modulation and the Encoder to IPTS in. Set the Output to to suit your SDR. Set the output frequency. Now click the Start button on the FreeStreamCoder and then the Tx button on the Portsdown. If all is well, the virtual LED on the FreeStreamCoder will change from Red to Green and a DATV output will appear at the RF output after a few seconds. When the transmission is stopped on the Portsdown, it's best to stop the FreeStreamCoder too.

A final reminder that the Pluto cannot handle H265 in this configuration. Don't try it as it confuses the Pluto, but the Lime Mini and the BATC Filter/Modulator board can take both H265 and H264.

Conclusion

This is a reasonably stable configuration for standard HD in a 333kS/s transmission for most uses that amateurs need such as talking heads and videos without lots of fine moving detail. There's an acceptable delay of between 5 and 7 seconds between input and RF output. It has been run for over an hour without skipping frames on a Core i5-10500 PC with an nVidia RTX A2000 6GB graphics card. Your mileage may vary depending on your hardware specs. It should be used as a starting point for your own experiments with OBS and FreeSteamCoder.