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Open Source Scan Converter

ossc

The Open Source Scan Converter is a low-latency video digitizer and scan converter designed primarily for connecting retro video game consoles and home computers to modern displays. It converts analog RGB or component video signals into a digital format, and doubles (or triples) the scanlines of a single frame if necessary to generate a valid mode for digital TVs or monitors.

The board and firmware originated as a homebrew project in 2015. The primary goal of the OSSC project was to create a scan converter with minimal latency and reasonable cost, which could also be assembled by hand. Output image quality and features have also been important targets as long as they didn’t contradict with the project’s primary goals.

Due to interest in the retro gaming community, both DIY kits and pre-assembled boards were first released to the public during early 2016. The firmware of the system is open source (hence the name) and new features can be added as time goes on.

If you’re new to the OSSC and scalers/processors in general, you may wish to start with the quick start guide here.

There’s now also an excellent getting started video tutorial, kindly created by RetroRGB, that you can view here.

Features

  • Detection and digitization of various analog SDTV/EDTV/HDTV/PC modes
  • Line double support for 240p, 480i, 288p, 576i, 384p, 480p, 576p
  • Line3x/4x/5x/6x support for 240p/288p with different sampling modes
  • Very low latency (less than 2 input scanlines)
  • Fast “deinterlace” for 480i/576i and 960i/1080i
  • Fast recover from input video mode change (e.g. 240p<->480i)
  • All video processing done in RGB domain – no conversion to YCbCr
  • Video and sync LPF for less-than optimal input signals
  • Multiple inputs supporting various formats (see below)
  • Full-range 24-bit RGB output through DVI/HDMI
  • Emulated scanlines with configurable strength and position
  • Configurable mask for overscan area
  • Selectable sampling configuration for 480p input: DTV-480p or VGA 640×480
  • Selectable CSC configuration for YPbPr source: Rec. 601 or Rec. 709

Power

OSSC requires an external DC power supply. A unit that outputs 5 volts DC with at least 1 Amp will work. The tip must be 2.1 x 5.5mm and centre positive. Suitable power supplies can be purchased from VideoGamePerfection.com or from any good electronics retailer.

If desired, a USB to Barrel Jack adapter can be used. This will function correctly as long as the USB port or charger used in conjunction with OSSC outputs at least 1 amp of current. Such adapters can often be found on Amazon or other popular retailers.

Do not use a power supply rated for AC output, or a power supply rated higher than 5 volts DC, doing so can damage the OSSC (especially v1.6 and earlier which have limited protection).

Using a supply that provides less than one amp of current may cause the OSSC to reset, especially when outputting at higher resolutions. You can however, safely use a PSU rated at least one amp or higher.

AV inputs

AV1 (RGB-SCART)

This input supports video in RGBS, RGsB (sync on green) and YPbPr formats. Composite video, luma or composite sync can be used as a sync source in RGBS mode. External sync splitters or boosters are generally not required or recommended as there is a built-in sync filter & separator in the ADC frontend. The sync input has 75 ohm termination, so a TTL-level sync signal should not be directly connected to the OSSC in order to avoid unnecessarily stressing the source console and/or OSSC. A 470 ohm series resistor on the console side of the cable is generally a good solution when using cables which are wired for the TTL-level sync output of a console. The video inputs also have standard 75 ohm termination, so arcade boards may need extra resistors on the cable when connected directly without using a Supergun.

AV2 (Component)

The AV2 input is a set of three RCA connectors which supports both component video (YPbPr) and RGB (RGsB format).

AV3 (VGA)

The AV3 input is a VGA/HD-15 connector which supports video in RGBHV, RGBS (pin 13), RGsB and YPbPr formats. RGBHV and RGBS modes require clean TTL-level sync signals and cannot extract sync from composite video or luma. AV3 is best suited for high-quality input sources as video LPF functionality is limited (the AV1 and AV2 inputs are routed through a dedicated LPF chip). Therefore, it is generally recommended to connect older consoles and arcade boards to these other inputs.

AV outputs

HDMI (DIY boards, v1.6 and newer pre-assembled boards)

DIY and newer pre-assembled boards contain a HDMI connector which is used to transmit video data in 24bit RGB format. Digital audio output is available on v1.6->, while it can be added via an add-on board for earlier boards (see below) . Currents up to 200mA can be safely supplied via DDC 5V power pin to external devices such as active cables.

DVI-D (v1.5 and earlier pre-assembled boards)

First revisions of pre-assembled boards came with DVI-D connector due to connector robustness and HDMI licencing worries. Functionality is otherwise similar, and it is possible to use a DVI-to-HDMI cable or adapter to connect to a HDMI display. Analog output pins of DVI are not used, so it is not possible to connect to a VGA monitor via a passive DVI-to-VGA cable or adapter (an active adapter is required instead, see below).

AV1 audio

Analog audio from SCART input is bypassed to a 3.5mm stereo output jack next to video output connector. On v1.6-> boards the jack alternatively functions as AV2 audio input, selectable via a miniature switch.

[Optional] Digital audio output for v1.5 and earlier boards

Borti4938 has created an add-on board that implements audio digitization and integration into HDMI output, which neither are natively supported by earlier OSSC boards. Both SCART input and 3.5mm connector (normally output) can be used as audio input, but it is highly recommended to have only either one of those connected at time since they are wired together internally.

All v1.5 and earlier OSSC boards are compatible with the mod (with -aud firmware), but required installation effort depends on OSSC/mod PCB versions. More information is found at the Github page of the mod.

[Optional] Analogue output

The OSSC does not come with an analogue video output, however this can be added easily by using a simple DVI or HDMI to VGA adapter. See analogue video output options for OSSC for more information.

Compatibility and special configuration

We encourage the community to add sections under each system instead of having an enormous table here. That way we can have more detailed and specific information on a per system basis, and here links to all the systems tested so far. A link to a summary page of potentially incompatible systems is found at the end of the list.

Home consoles

Computers

Arcade Boards

OSSC potential incompatibilities

See also Optimal timings.

Televisions, Monitors, Processors etc

The community is constantly testing displays and related hardware with OSSC. While it is an insurmountable challenge to test every display, the data that’s been collected is nevertheless often useful. Initially this data was saved in a Google Docs spreadsheet, but for a more permanent record I’m starting a page here.

OSSC Display Compatibility

TV compatibility thread

More information on Wiki page

Firmware download on GitHub

PCB and gerber files download on GitHub


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