Output 240p at 120Hz on the regular OSSC?

NewHome Forums OSSC, OSSC Pro and DExx-vd isl OSSC – Feature Requests Output 240p at 120Hz on the regular OSSC?

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  • #46714
    Analog Dude

    Would it be possible for the OSSC to ever take a 240p 60Hz signal and convert it to 240p 120Hz so that we can have true 240P on a PC CRT monitor? Maybe on a custom firmware or something?


    Since the OSSC doesn’t have a frame buffer, it can’t repeat entire frames but only individual lines and samples. There is probably not enough RAM available onboard the FPGA to buffer more than a few lines of video at a time. Maybe the OSSC Pro might be able to repeat frames.


    AFAIK to get the correct effect you don’t have to repeat the frames, just inserting a black one in between.


    Even a 120 Hz mode to simulate CRT flicker would require a buffer since the fields get output twice as fast. The OSSC would need to buffer a full field (224 to 240 lines) while it outputs the picture. As it runs through the buffer, it gradually catches up with real time.

    Depending on the captured resolution, it would require buffering between 215 kiB (320 x 224 x 24 bpp) and 461 kiB (640 x 240 x 24 bpp).

    120 Hz with black frame insertion might also not create the desired effect, but a more flickery picture than CRT TVs have.

    The OSSC Pro might be able to do it if the HDMI Tx permits, I guess. Hopefully @marqs or someone else involved in the design could clarify this.


    Many modern TVs with support to 120hz, like LG OLED and Samsung QLED, also greatly benefit by running at 120hz because it reduces input lag, even in game mode my Samsung Q80 have an average ~9ms of input lag in 60hz, but only ~5ms while running at 120hz.


    As mentioned above, not possible with the original model but OSSC Pro can do 120Hz. It’s worth noting that for 60Hz->120Hz conversion (BFI or frame duplication) at least 1/2 input frames need to be buffered, i.e. first lines of output are drawn 8ms after input.

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