Capture Sizing and Aspect Ratio

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  • #23423
    SavagePencil
    Participant

    This topic is similar to @Cae’s thread around Aspect Ratios ( https://videogameperfection.com/forums/topic/aspect-ratio/ ), but I’m trying to find guidance for the correct settings when capturing video from the OSSC.

    For example, if I output a default 4:3 240p input thru a vanilla OSSC set to Line2x, I believe it’s correct to capture that footage at 720×480. It will have some overscan, but that capture takes into account the 4:3 nature of the input, despite 720×480 being 3:2. Is that assumption correct?

    If that’s how I’m running my footage to OBS, I just need to set my scene to 720×480, right?

    On some of the more optimized OSSC profiles, such as FirebrandX’s optimized settings, my Datapath VisionAV-1 sometime recognizes the output as non-standard resolution. As an example, when using FBX’s 256×224 profile for Genesis games in Line2x mode, the capture card sees it as 768×480. Should my OBS scene continue to capture at 720×480, or increase to the new size?

    #23424
    nmalinoski
    Participant

    Yes, even though 720×480 is a 3:2 frame, I believe the visible portion of the image was intended to be stretched to fit a CRT (which can result in non-square pixels).

    480p modes can range from 640×480 out to 888×480, but 768×480 isn’t one of them. Instead, it’s a standard VGA resolution (WVGA) with a 16:10 ratio. It’s possible your capture card simply doesn’t like it (I don’t think many devices actually support this resolution), but you might get okay/good results capturing it as 720×480.

    #23433
    paulb_nl
    Participant

    If you want to record 720×480 in 4:3 then the scene should be 640×480. But why record in such a low resolution? You should at least let OBS upscale it before encoding if your capture card does not support the higher line modes.

    The optimized modes are a special case. The correct aspect ratio for 256×240 in Line2x is 256×2 x 8/7 = 585×480.

    For best quality capture you should set your capture card to XRGB format. The default is NV12 which is 4:2:0 so the video is already being chroma subsampled before it reaches OBS.

    #23434
    SavagePencil
    Participant

    Yes, I have OBS doing full 4:4:4. I was using the low resolution as an example for simpler math.

    Just to be clear, I should resize the 768×480 down to 585×480? It appears to be using the full size of the image.

    #23436
    paulb_nl
    Participant

    Yes and 1170×960 for X4 and 1462×1200 for X5.

    FBX made a video about setting the correct aspect ratio on the Super Nt which also applies to 256×240 optimized.

    https://youtu.be/Hr6KgNXXRxs

    #23437
    SavagePencil
    Participant

    Does the 8:7 apply to NES/SNES specifically (256×224) or does it also apply to the Genesis in 256 mode (256×240)? Similarly, for Genesis in 320×240, would the multiplier be 4/3?

    (Thank you, BTW!)

    #23438
    paulb_nl
    Participant

    It should apply to all those consoles because they pretty much have the same timings: 341 total/256 active for (S)NES and 342/256 for Genesis. I don’t know where the calculation came from but the 8:7 ratio is not related to the 8:7 ratio of 256×224. Actually NES and SNES are also 256×240 but SNES just outputs 8 black lines at the top and bottom to have some more time in Vblank so it can load more data into the PPU.

    I have no idea about the Genesis 320 mode. If you would capture at line2x generic 4:3 and resize it to 640×480 then the width of the image without the left and right borders should be close to the correct resolution.

    #23439
    SavagePencil
    Participant

    Thanks for the tip on the 8:7 not being correlated to 256×224. Will the same approach you suggest for Genesis 320×240 apply to oddball resolutions like 352×224 on the Saturn?

    #23441
    Harrumph
    Participant

    for Genesis in 320×240, would the multiplier be 4/3?

    For genesis, the multiplier is 32/35. You’ll find the width is actually exactly the same as for 256 mode; 320*32/35=292.57 & 256*8/7=292.57.

    You can find some more dotclock rates/pixel aspect ratios here: https://pineight.com/mw/index.php?title=Dot_clock_rates

    #23442
    SavagePencil
    Participant

    Whoa, this is pretty nuts! Two follow-ups:

    1. Is it better to round UP (292.57 -> 293), DOWN (292.57 -> 292) or to the nearest even value (292.57 -> 292)?
    2. How would I get the dot clock rates for Saturn (320×224, 352×224, 704×224) and PC Engine (352×240, 512×240)?

    #23445
    Harrumph
    Participant

    1. You’d generally want apply your upscaling multiplication before rounding. On the other hand, you might also want an even number, as an image with uneven number pixels will be off-center by 1 pixel. Tbh, it will not make any discernible difference if you just go with even numbers.

    2. TG-16 352 mode is listed in the linked page, looks like PAR there is 6:7. The 512 modes are just double speed 256. For Saturn I don’t remember, but this was talked about in another thread I believe. EDIT: dug it up, it has same PAR as TG16 352 mode (6:7): https://videogameperfection.com/forums/topic/saturn-optimal-settings/#post-20857

    #23447
    SavagePencil
    Participant

    Thank you for that! In an effort to teach me to fish, can you explain how we get from the dot clock rate to the PAR? I’m having trouble seeing the correlation between Exact Frequency and PAR. Where does the frequency divisor come from?

    Are the numbers for Saturn here accurate? https://segaretro.org/Sega_Saturn/Technical_specifications#Video

    If so, how would I use those numbers to get to the 6:7 aspect ratio of 352×224? Can I use them to get the PAR of the 320×224?

    #23448
    paulb_nl
    Participant

    I don’t think you can use the pixel clock. You need the exact horizontal line timings to calculate the PAR.

    Take the NES for example. Here are the timings: https://wiki.nesdev.com/w/index.php/NTSC_video

    The active video of the NES is not just 256 but actually 256+15+11+1=283 pixels because of the left&right borders. So a CRT would display the 283×240 resolution in 4:3.

    Scaling this to a 4:3 resolution like 320×240 means you have a ratio of 320/283. 320:283 is 8:7.075. Hey that ratio is familiar 😀

    #23450
    Harrumph
    Participant

    Sure you can, afai understand it. Everything in the table is in relation to the pixel clock defined by Rec.601, 6.14 MHz for square pixels in 4:3 aspect ratio. So divide by the dot clock of the console and you get the console PAR.
    NES: 6.14/5.37 = 8:7
    Saturn: 6.14/7.16 = 6:7

    Of course can’t use the rounded numbers to get the exact ratios, but you get the idea.

    PS Actually I don’t know if the ”6.14 MHz for square pixels” was defined directly in Rec.601 (never read it), but it checks out when compared to the pixel clock of 480i video, where it’s 13.5 MHz for 858 samples with 10:11 PAR. (13.5*10/11)/2 = 6.14. (divided by two since it has double horizontal resolution compared to 240p)
    So 858 samples for 704×480 -> 780 samples for square pixel 640×480 -> 390 samples for 320×240.

    #23468
    SavagePencil
    Participant

    Really trying not to be dense here, but I’m still struggling with how to get some of these straight. I proved it out by measuring them with a ruler today, and putting together this spreadsheet:

    https://docs.google.com/spreadsheets/d/1WoRFwFejaDGvePbJoHUsy4eZ_MRXm9ETvsPR5xqWsik/edit#gid=1954283489

    My remaining questions:

    1. Where can I get the exact horizontal timings for the Saturn 320 and 704 modes? I feel like these numbers are staring me in the face, but I’m not sure I’ve got it down properly. For example, I can’t figure out how to calculate the NES 283 number that @paulb_nl cited, except for using the NESDev wiki he linked to.
    2. How would I go about getting the numbers for the Jaguar or GameCube?
    3. Why are the AES and MVS different? I thought they were using the same hardware?
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