OSSC Pro for CRT Downscaling

[bjbdragon]

I’m attempting to use the OSSC Pro (with addon Extra AV Out board) as a downscaler for an NTSC CRT TV (15kHZ). As there’s no native CVBS/S-video outputs, I purchased a RetroCastle RGBHV to CVBS/S-video adapter. The OSSC Pro does seem to handle the basics of scaling and output, except for an intermittent alternation between 480i and 240p output. I was able to get proper 480i output by tweaking some of the advanced timing settings, but no matter what I try it’s not consistent. Maybe it’s an issue with the RetroCastle which is based on AD724, but I’m not really sure.

The main thing I’m wondering how to do is adjust black level, white level, white balance, NTSC pedestal, or really anything in regards to the output. I see brightness, contrast, hue, pedestal, etc. in the Legacy AV input board settings, but not for output. Is there really no way to adjust any of that for output.

• This topic was modified 4 months, 2 weeks ago by bjbdragon.

[BuckoA51]

There is no alternation on the output of the extra av out unless the source signal changes. When this happens, is it changing on the OLED display at all?

First of all, use the test patterns to determine if the signal is stable with your converter. If it is, the issue is likely with the signal you’re trying to downscale.  Can you tell us your full video chain?

[bjbdragon]

There is no indication on the OLED display at all, nor the “information” OSD. The source I was using was AV4 HDMI, but the same issue occurs with the test pattern in 480i. When it bounces back and forth, there’s no cut out at all. It’s also not a perfect 480i, it’s more jittery.

As far as AV output, I’ve used the Extra AV Output board, or HDMI to several different HDMI->VGA adapters. Finally, I’m using the Retrocastle adapter to adapt to the TV itself.

• This reply was modified 4 months, 2 weeks ago by bjbdragon.

[marqs]

What is your perfect 480i? Keep in mind that there is no flicker filter so picture will have more bobbing that e.g. PS2-era or newer consoles.

As for output controls, the ADV7125 DAC is 8bpc and only covers the standard 0.7Vpp range so it doesn’t make sense trying to correct downstream deficiencies on Pro but instead generate as close to reference level output signal as possible. Ultimately the composite encoder or receiving display should have controls over gain, offset,  pedestal etc.

[bjbdragon]

I’m not sure what you mean by “What is your perfect 480i”. I’m getting 480i output some of the time, but alternating fields is intermittent. That is, it’s putting out an interlaced picture, but it’s putting out only even or odd fields, not both. The default video timings produced this 100% of the time. I see, the lack of a flicker filter could be an issue for me, however this is a problem that doesn’t just happen with specific patterns, it’s clearly a sync problem.

And I do appreciate the comment regarding signal output levels. My current Y/C encoder (RetroCastle with AD724) doesn’t have any such controls, and I’m currently using the S-Video output. Do you know of a particular known good encoder, that has such controls? I don’t want to have to alter display levels, as I use actual old video game consoles and tapes, which have the expected signal levels and don’t want to have to change it every time I change inputs.

And yes, I’m aware that the RetroCastle adapter might actually be the issue, hence why I’m asking for suggestions of other adapters (beyond just needing a way to adjust the output levels). Also, I do need both S-Video and Composite outputs.

• This reply was modified 4 months, 2 weeks ago by bjbdragon.
• This reply was modified 4 months, 2 weeks ago by bjbdragon.

[Qaraqual]

@marqs

Thanks for the latest v0.81 update – stability fixes are much appreciated!

I’d love to see an optional **line blending mode for low-latency downscaling** (as alternative to decimation/dropping lines) in Line Multiplier / Adaptive modes. This would blend input lines (e.g., average 3 lines for 720p→240p) to reduce shimmering/artifacts on non-integer scales, while keeping near-zero lag – doable line-by-line with Cyclone V FPGA + SRAM/LPDDR2.

I created a GitHub feature request here: https://github.com/marqs85/ossc_pro/issues/35

This would make OSSC Pro even better for modern PC games downscaled to CRT perfectly, without full scaler lag (~1.5 frames).

Anyone else interested? +1 for priority! 🚀

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