Reply To: OSSC Pro: P-LM 576i passthrough gives distorted image

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April 19, 2024 at 5:49 PM #61293
Zacabeb
Participant

    The strange thing is that the receiver accepts the output of the OSSC Classic in passthrough mode. I tested inputting a 576i signal to the OSSC Classic and changing the VIC from 0 to 21, 22, 25, 26, (with Full TX setup enabled) but the HDMI TRX in the receiver doesn’t even seem to care about whether or not the VIC corresponds to the actual timings (thus I imagine that sending the appropriate VIC on the OSSC Pro wouldn’t make a difference).

    It could be a bug in the HDMI TRX itself rather than the OSSC Pro, but it’s an interesting phenomenon. Since it has no issues with the OSSC Classic it must be triggered by some metadata that differs between passthrough output of the OSSC Classic and OSSC Pro (or between P-LM and A-LM passthrough on the OSSC Pro). It might be a non-issue since standard definition P-LM passthrough isn’t particularly important given A-LM is working fine, but the issue might happen with other timings as well.

    I wouldn’t be surprised if the HDMI TRX is to blame since there seems to be all sorts of issues with those (Panasonic/Nuvoton in particular).

    Edit:

    I’ve done some more testing, including using the OSSC Classic routed through the OSSC Pro via HDMI. The results are the same.

    What I found though is that if I enable picture processing in the receiver, I get a different error altogether. When the FPGA in the receiver does picture processing, the HDMI TRX first converts the input to YCbCr 4:2:2 8 bpc, then sends it to the FPGA. Now the picture gets another error instead; all the pixels are there but the Cr samples get replaced with Cb, with the chroma samples interleaved. This makes the OSSC Pro menu turn from blue to magenta with a red border on the left edge and a blue border on the right edge. Hmm.

    The same effect occurred regardless of whether the OSSC Pro was set to output RGB or YCbCr.

    So there probably is something about the pixel repetition the HDMI TRX doesn’t like. But this is where things get weird, since it accepts the output of the OSSC Classic in passthrough mode and doesn’t even care what the VIC is set to. Maybe the PR bits are set wrong in P-LM passthrough mode on the OSSC Pro?

    • This reply was modified 1 year, 10 months ago by Zacabeb. Reason: More findings, more confusion