HDMI to SDI for Sony BVM A series

[atohmdiy]

Hello all

I am much in retro gaming recently, i bought a mister and a saturn (and it's strange to have one again after 20 years ).

I also bought two bvm 2010P that need repair. I am working on them the last few weeks, power supply are defective but i think i will find the problem soon

But i have something in my mind that i want to discuss. When i was looking for a BVM, i found a seller near that offer a BVM-A20F1U for a very decent price. Of course it's without the expensive 68x board... this input board is really a plague for this series.

However i am asking myself something. Most people buy a BVM for RGB input, it's obvious as retro console like my saturn have no digital video out. So in fact every retro console have an integrated DAC that can output different analog signal (rgb, composite etc). Mister fpga is the opposite as the only output is hdmi. Recently they add the direct video mode that i will use with my bvm once repair, it send the raw digital signal from cores (240p for almost everything) to hdmi, and to work you need a dac (hdmi to vga adapter) plus a vga to BNC adapter with the right number of sync cable (one in my case as it is composite sync in my bvm).

But what if i use this direct video mode of my mister with a hdmi to sdi adapter, do you think it will work with the A20F1U and 240p ? I look for it but i really don't know much about SDI. I am not even sure that the HDMI to SDI is lossless conversion, as i think i red something about this a few month ago. So if this doable, what would be the image quality ? I don't find much info in sony bvm documentation, and in fact sony even avoid to say 240p is compatible with bvm A and D series, they say 15 khz 480i is ok but no info of 240p We know it compatible of course, but it's only to said they don't make this info apparent, like 240p was a thing of the the past that need to be hidden, or maybe it was too obvious It's pretty much the same with all hdmi to vga adapter. Most will support 240p, but if you look to the spec it will say 480p is the minimum.

Anyway, if this is doable it could be very interesting for people that own a mister and want a bvm for cheap compare to expensive D series. A series could be find for cheaper than other BVM series and the fact that RGB is not possible is a solid base to discuss the price.

Best regards

[Fudoh]

it send the raw digital signal from cores (240p for almost everything) to hdmi

does it? I was under the impression that the 240p HDMI output is supersampled, so it ouputs a very high horizontal resolution to stay within the HDMI minimum specs.

The SDI inputs on the Sony have rather narrow specs. The signals need to be extremely close to SMPTE timings. 240p via SDI is not supported. 480p can be supported, but I think it isn't on the Sonys.

Image quality from HDMI to SDI is great. Most converters are 4:2:2, but since you'd be running line doubled or tripled resolutions that doesn't really matter. Using SDI you can very well use an A-Series BVM these days, it's just not as pure as connecting 240p through an analogue input.

If you want to give it a try, then you need a scaler and you need a HDMI to SDI converter. The latter one's easy. The first one needs a decoupled output, so you can get standard refresh rates. You can use a device like the Framemeister or you can use an OSSC and add a secondary scaler that you do this for you (e.g. OSSC > Extron DSC 301 or HD-HD > HDMI to SDI converter). The results are very nice.

[atohmdiy]

it send the raw digital signal from cores (240p for almost everything) to hdmi

does it? I was under the impression that the 240p HDMI output is supersampled, so it ouputs a very high horizontal resolution to stay within the HDMI minimum specs.

The SDI inputs on the Sony have rather narrow specs. The signals need to be extremely close to SMPTE timings. 240p via SDI is not supported. 480p can be supported, but I think it isn't on the Sonys.

Image quality from HDMI to SDI is great. Most converters are 4:2:2, but since you'd be running line doubled or tripled resolutions that doesn't really matter. Using SDI you can very well use an A-Series BVM these days, it's just not as pure as connecting 240p through an analogue input.

If you want to give it a try, then you need a scaler and you need a HDMI to SDI converter. The latter one's easy. The first one needs a decoupled output, so you can get standard refresh rates. You can use a device like the Framemeister or you can use an OSSC and add a secondary scaler that you do this for you (e.g. OSSC > Extron DSC 301 or HD-HD > HDMI to SDI converter). The results are very nice.

My knowledge on analog / digital video is very limited, my thing is more digital audio in fact
But from what i understand with mister, if you take the analog board they made it's a basic 18 bit R2R dac, with 3x6 channel of RGB data, plus Hsync and Vsync. It's then direct data from what the core output. I think they do the same with their direct video mode over hdmi just redirecting the data. Also in their wiki they said it's out of the hdmi official spec and not all DAC are compatible. Quote from Mister Wiki :

Once it's enabled, it allows your HDMI port to output the raw and unprocessed digital audio/video signal from the loaded core, which is consumed by your DAC. MiSTer will not work with your HD TV or monitor while this mode is enabled, since they require a standard HDMI signal to work, and the zero-lag Direct Video signal IS NOT standard HDMI.

I just read again the sony A series doc and i finally get it, you are right 240p is not supported, but 480i or 480p is. The 68x is said to support 525/59.94/1:1 (240p) and 525/59.94/2:1 (480i). With SDI it's only 525/59.94/2:1 supported.
However i don't think you need an upscaler for anything. Mister can do everything an upscaler can do, and instead of 240p direct video mode you can use the mister scaler to output 480p / 31 khz directly. However i don't now if i am a big fan of upscaling 2d content, as you said in that case RGB will be the purest for 240p content.

[Fudoh]

The 68x is said to support 525/59.94/1:1 (240p) and 525/59.94/2:1 (480i). With SDI it's only 525/59.94/2:1 supported.

can you link to the document? I don't understand what the 1:1 and 2:2 is refering to. I doubt that Sony die EVER anywhere state official 240p compatibility.

For MiSTer you don't need an upscaler, that's right, but the SDI ports don't support 480p, hence the need for 720p instead. If the SDI inputs supported 480p, then be off pretty good, since 480p with 100% scanlines looks extremely close to 240p on these particular monitors.

Also, when going for SDI, you can't use the low latency video modes on the MiSTer, so if - in pure HDMI mode - the refresh is coupled to the actual cores, then you're very likely running into massive problems when converting to SDI, since the refresh rates are too far off from standard specs. When using scaled output, you can get around this by letting the MiSTer re-time your output to a more compatibly refresh rate.

[atohmdiy]

You can find the doc here :

https://archive.org/details/sony_BVM-A_series

Edit : you were right in what you said, i read wrong. So in fact sdi support 480i only, hd sdi 720p and various 1080. 68x support nearly everything... but 240p is not official.

[Fudoh]

From what i understand, 1:1 is progressive and 2:1 is interlaced. So 240p is officially supported only on the 68x,

you're right. 1:1 is progresssive and 2:1 is interlaced, BUT you overlooked the line frequency. 525/1:1 is a 31khz timing, so the spec lists 480i and 480p as supported, not 240p.

And as suspected SDI doesn't list 480p, just 480i, 720p and 1080i, so you can't use a 480p source with a HDMI to SDI converter.

[Guspaz]

Be careful. 480p is not NTSC, and is not part of either the SD-SDI or HD-SDI specs. It is ED-SDI, which almost nothing supports. The ED-SDI (480p) standard was not written until a few years after the HD-SDI (720p/1080i) standard, in 2000.

The BVM A do not support digital 480p input. On page 5, it is only listed as being supported by the analog inputs. 240p support is not mentioned anywhere at all.

[atohmdiy]

As i said in my edit once i realized my mistake, you are right. It's a shame really, i really dislike interlaced resolution, and honestly i am not so sure 720p will be great with mister upscaler compare to 240p or 480p. Even in composite you are limited to 480i. It seems these poor A series are doomed to be useless until someone decide to make a copy of the 68x, and it's almost sure it will never happen.

Maybe to play with more modern console like playstation 3 in 720p this could be interesting, but it's not retro gaming anymore.

[Unseen]

does it? I was under the impression that the 240p HDMI output is supersampled, so it ouputs a very high horizontal resolution to stay within the HDMI minimum specs.

It's... complicated. Anything below 25MHz pixel clock requires pixel doubling. However, all forms of pixel replication(*) also specify that all of the replicated pixels must be identical and that the destination device should (or must, not sure) discard all but one of them. So the transmission on the wire is technically supersampled, but the actual input to the display's video processor might not not be.

(*) There are modes that specify higher replication counts, IIRC up to 10x for the 2880x(240/288/480/576) ones that are meant for 1:1 pixel mapping of low-res consoles/computers

[Fudoh]

in a real life scenario the question would boil down to whether MiSTer > HDMI 240p > DAC > OSSC still allows the OSSC to use it's optimized sampling options. Wanted to try this for a few months now, but never got around to it. Maybe somebody else tried and can share some thoughts about it?

[mimylovesjapan]

Hi there !
I have a question for Fudoh !

OSSC > Extron DSC 301 or HD-HD > HDMI to SDI converter

Why do we need a HD-HD device here ? OSSC doesn't outpout HD resolution ? I thought it could do like 720p or something...

[Guspaz]

The OSSC is a line doubler (or more specifically a line multiplier), not a scaler, so any non-standard video timing output by the source console is reflected in the output signal. Yes, it can take a 240p input and scale it to 720p, but I'm not sure any 240p console actually uses exactly standard NTSC timings, and so either the HD-SDI converter or the display would probably reject it. For example, with an NES or a SNES, you will get 720p at 60.1 Hz, but you need it to be at 59.94 Hz.

Even a scaler will have to make compromises of course. You're probably not going to do frame blending to handle the framerate difference, so most scalers will probably just drop frames to do the conversion, resulting in uneven frame pacing (hitching or skipping), which is not good. You would actually get a better result using something like an Analogue FPGA console (or I assume the MiSTer does the same thing) where they have the ability to very slightly underclock/overclock the source console so that they can output at exactly the standards-compliant framerate. Yes, your games will run around 0.3% slower in the case of the NES/SNES, but that's the cost of getting smooth frame pacing and motion without introducing additional latency.

[kamiboy]

Isn't there a guy doing reproduction BVM RGB input boards. They were still costly, but well worth the price. Just get one of those instead of trying to fit a square peg in a round hole. SDI has no broad utility for retro gaming, except perhaps for 7th gen consoles, and even then I am sure with plenty of caveats. Stick to an all analogue pathway and avoid the pain train of endless daisy chained bespoke devices to force an inelegant solution to work.

[mimylovesjapan]

Yes, you are right. It would be not so interesting the get digital chain on CRT. Dots visible, introducing lag, etc... not so different than a OSSC + LCD screen at the end.