RetroArch Disc Project – Alpha testing has begun! Details inside

Libretro Team

Ever since the announcement earlier on June 30th, we have been working hard on the RetroArch Disc Project, and we are now getting to the stage where we want users to start alpha testing the latest code.

We invite you to come over to our Discord channel (also linked to on the RetroArch website – click on the tab ‘Discord’)- and join the channel #discordproject.

How to apply for alpha testing

For the purpose of this alpha test, we need you to meet the following requirements:

  • You are using the latest nightly versions of RetroArch (available here).
  • You are using RetroArch on PC, and are running either Linux or Windows with the CDROM support included.
  • Make sure the cores you are going to be testing are the latest up-to-date versions. Update them daily from the Core Updater if unsure – the cores should have physical CDROM support, otherwise the testing won’t work.
  • You have an optical disc drive (either USB or internal, any CD-ROM/DVD-ROM/BD-ROM drive should do).

Report issues you’re having with physical CDROM playback. Be as detailed as possible in your feedback – we are especially interested in which optical disc drive you’re using.

Be prepared that you might be asked by a moderator to run ‘retroarch_debug.exe’ and return a log message back to us in order to learn more about the issues you’re having. ‘retroarch_debug.exe’ is a debug executable that should be shipped with every RetroArch nightly version for Windows. For Linux users, we assume that they can build from source and compile with CDROM_DEBUG=1 manually in order to run these more detailed debug tests.

Compatible cores

Listed below are some of the cores that we added physical CD-ROM support to, and the ones that we would like you to test –

  • Beetle PSX (HW and non-HW)
  • Beetle Saturn
  • Genesis Plus GX
  • 4DO
  • Redbook Audio Player (Audio CD core)

We have also added support to more cores, but for now we want to go with these cores as they have been most extensively tested.

A couple of known edge cases:

  • Beetle PSX HW: The ‘vulkan’ renderer can exhibit issues where either the CD will not work, or some other corruption issue will manifest itself. We recommend you use ‘opengl’ or ‘software’ for now while you test CDROM.
  • Beetle PSX HW: Make sure the core option ‘CD Access Method’ is not set to ‘precache’. If you do, real discs won’t work.

How to load discs

1.You need to first start up the core itself (there is no automatic system detection yet when you insert a disc).
Go to Load Core, and select the core you want to use.

2. Once the core is loaded, select ‘Load Disc’.
3. It will now list all optical drives. Make sure the disc you want to use has been inserted into the optical drive tray and make sure the tray is closed. Then select the drive. The core will now start with your CDROM as input.

How to dump discs

RetroArch can dump discs to internal storage in bin/cue format. The video above will show you how.

  1. Select ‘Dump Disc’.
  2. It will now list all optical drives. Make sure the disc you want to use has been inserted into the optical drive tray and make sure the tray is closed. Then select the drive.

The disc will now be dumped to the ‘Downloads’ directory. It will continue showing the progress bar until the operation has finished. In the meantime, you can play any core/game (as long as it doesn’t involve real CD playback) until the dumping has finished.

Redbook Audio Player – Libretro core for music CD playback!

As a testbed for the Disc Project, we made a redbook audio CD player Libretro core!

You can grab this core for Windows and/or Linux by going to Online Updater, and downloading it from the list (Redbook Audio Player).

Known potential issues

  • Right now, CDROM works better on Linux vs. Windows.
  • FMV playback with Beetle PSX HW has the potential to be slow on some optical disc drives on Windows. Cause yet unconfirmed.
  • There is a known issue with redbook audio – the redbook audio track begins a few seconds later from its starting period.
  • Libcrypt copy-protected PlayStation1 games will not work right now, but any other copy-protected PlayStation1 disc should.
    Here is a listing of some Libcrypt-protected games from Europe: https://hastebin.com/ruyacahuba.http . You can generally assume these won’t work.

New Vulkan graphics enhancements features in Beetle PSX HW!

Libretro Team

MDEC YUV filtering

PlayStation used a special unit called the MDEC to decode full motion videos instead of relying on software rendering (like the Saturn). These videos were encoded in YUV macroblocks and had to be converted from YCbCr to RGB so that the PSX can output the final image to the screen. A common issue with PlayStation emulators is that the chroma channel generally should be smoothed, but the PlayStation tend to leave it unfiltered.

There’s now a feature called ‘MDEC YUV smoothing’ which does filter the chroma channel. You can see the before/after screenshot above (video in question is the Resident Evil 1 intro) to see the kind of visual enhancement this brings to the picture.

SSAA (Super Sampled Anti Aliasing)


Some people prefer to play PlayStation1 games at native resolution and just applying a CRT shader at the end instead of running them at very high resolutions. However, there are some issues with that approach. 3D polygon graphics can tend to look very aliased and jagged and lacking in definition.

Alternatively, others like to crank the resolution up as high as possible. Both approaches have their pros and cons, but a definite disadvantage is that early 3D was very primitive so you might not want to see razor sharp angular polygons rendered at obscene resolutions, especially when a game relies a lot on pre-rendered backgrounds and other 2D elements. The Final Fantasy and Resident Evil games come to mind for one.

The option ‘Adaptive smoothing’ already exists and it attempts to distinguish 2D elements from 3D elements. It will smooth out the 2D elements but leave the 3D elements alone, resulting in a high resolution picture with the 2D elements not looking pixelated and ugly.

This new Vulkan-only option, SSAA, is a completely new approach. The image is rendered at the internal resolution you set it at (2x/4x/8x/16x, you name it). It then downsamples it at the final output stage back to a resolution somewhere in the ballpark of 240p. What you get is a low-resolution image with very clean anti-aliased 3D, kinda similar to the N64 actually which had native 8x multi sampled anti aliasing of some sort.

Certain CRT shaders expect a 240p-ish image to look their absolute best, so this option lends itself very well to that. It also can tend to look bit more coherent with mixed 2D and 3D in cases where adaptive smoothing fails.

Tip: We recommend you turn dithering off when using SSAA (Super Sampled Anti-Aliasing).

Example – Final Fantasy IX

Below you see SSAA in action with Final Fantasy IX on RetroArch. The first image is SSAA at 1x internal resolution. The second image is SSAA at 8x internal resolution. You can see how the downscaling does its magic in the second picture – it results in an image that almost looks like as if the polygon characters are part of the background itself.

Finally, a CRT shader is used – crt-royale-ntsc-320px.

Final Fantasy IX – SSAA at 1x internal resolution with CRT Royale
Final Fantasy IX – SSAA at 8x internal resolution with CRT Royale

Dithering for Vulkan

PlayStation and N64 output the final image at 16 bits per pixel. Since that isn’t a particularly wide colorspace, both systems used dithering in order to fake the illusion of a larger palette of colors. This combats color banding and wouldn’t be very noticeable at native resolutions on a CRT TV. On more powerful hardware and when emulated, the limitations of this approach become clear, and some would prefer either internally rendering the dithering at the internal resolution, or disabling it altogether.

Dithering was previously ignored by the Vulkan renderer and was always turned off, no matter what you configured. Now it will actually let you enable it. If dithering is enabled, the scanout image will be 16 bits per pixel. If it is disabled, the scanout image will be 32bits. We recommend that you turn dithering off if you are going to be using ‘SSAA’ (Super Sampled Anti Aliasing)