Ref Video (Genlock) over fiber

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poucedeleon

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Ref Video (Genlock) over fiber

PostSun May 11, 2014 4:43 am

I heard a rumor at NAB that ref video would not travel over fiber on the New Studio camera. You would need to run a separate coax cable. Can anyone comment on this?
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Re: Ref Video (Genlock) over fiber

PostSun May 11, 2014 11:30 am

Reference signals ( Blackburst and tri-level) are both analog signals. They will not travel on circuits meant for digital signals, and as far as I can see this is all BMD has made provisions for. We use a separate unit to transport analog video (including reference) over fiber.
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Re: Ref Video (Genlock) over fiber

PostSun May 11, 2014 7:07 pm

What BMD (and others) need to do is to include a reference input on the fiber optical receivers. Those units do some re clocking of the HD-SDI, but they do NOT reclock to a reference. There is no need to reference the cameras if you can reference the Fiber to HD-SDI converter. THAT would be handy.

And while they are at it, do a similar thing for the HDMI to SDI converters.

Basically, any time they reclock HD-SDI in a converter, it would be fantastic if they would provide a reference input for that reclocking circuit. Then anything could be easily timed.

They DO have a reference input on their UpDownCross converter. I have used it a few times as a cheap frame sync, by basically "converting" to the same format I started with - BUT with a reference input, allowing me to genlock that source.
Scott R Smith
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Gary Adams

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Re: Ref Video (Genlock) over fiber

PostMon May 12, 2014 3:16 pm

The Studio Camera will genlock in three possible ways. Reference input using tri level sync, SDI Video Input or Return feed over fiber. So you do not have to run an additional cable to the camera for reference.

Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostTue May 13, 2014 1:34 am

so gary, if you could clarify your previous post…

if we reference our ATEM to house sync, then DA its output to the return video to studio cameras, they will all "genlock" and be in common time without a connection to the reference input, correct? my cameras are usually thousands of feet away from the switcher and this would have to work while connected via fiber. we currently are using additional equipment to move the analog reference signal out to them, eliminating this need is very appealing to us. our system goal is to always be able to time the cameras and have them feed a video hub and subsequently the rest of the system, and be able to do clean cuts between them on a router output into a recording device. having them so far away and apart is always a complication for us, and anything to streamline this helps. I have only noticed the reference input method to sync in your manual, maybe you guys should make this feature more apparent...
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Re: Ref Video (Genlock) over fiber

PostTue May 13, 2014 2:24 pm

Hello Greg. Let me describe our workflow involving our ATEM switchers and multiple cameras. Your flow would be different but similar. The studio cameras have our Camera Converter built in providing bi directional video, audio, and intercom to/from the camera. When using our ATEM switchers, Tally and CCU controls are made available via the return video feed. You would connect our studio camera with bi directional fiber to our Studio Converter (basically 4 camera converters in a 1RU chassis). The Studio converter provides SDI (with audio) from the camera to feed the ATEM (or router). Analog audio is also available as well as an intercom station as part of the Studio Converter. Now. you would feed a program our auxiliary output from the ATEM to the Studio Converter PGM SDI input. This effectively distributes program video to all of the cameras back via fiber. While it is intended to be program or AUX video from the switcher, it can be another source of SDI video (not sync or reference). This video returning to the camera via fiber may be selected as a genlock reference. If you genlock the ATEM switcher (using tri-level sync), the Program or Aux output will be locked and may be used to genlock the camera. I recommend this since the Program or Aux output of the ATEM switcher will carry the tally and CCU control to our camera. If you feed some other source, the camera may also lock but it will not have that return information should you wish to utilize it. If you do not wish to utilize the features of the ATEM or Studio Converter, you could use our SDI to Fiber converter and feed video for genlock and receive video back from the camera. In the camera menu, there is a selection for the source of genlock as well as controls for precise timing of the output video signal. Sorry to be long winded. I wanted to describe as best I could for your purpose. If you wish more detailed information, please PM me.

Best Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostTue May 13, 2014 8:53 pm

So, what you are saying is, you can utilize the ATEM Program Output on an SDI signal to Genlock a camera over fiber.

I'm not saying you aren't telling me the truth, but that idea really flies in the face of all traditional concepts of genlock, and how it works. First off, you could not traditionally ever genlock off of the output of your switcher, since it's timing is already behind the timing of the inputs. I mean, the inputs are timed to arrive at the switcher at the same time. The switcher's output, by definition HAS TO OCCUR AFTERWARDS.

Next, when everything else in the world is using TLS or BLS, an analog video format, to sync instead of SDI, how is it that you can easily use SDI for accurate sync?

That said, timing/genlock/reference is so much more forgiving and easy in the world of SDI that I wouldn't be surprised that you are 100% correct - even if it doesn't make any sense.

Doggone whipper-snappers! Back in my day, you had to time all of your sources horizontally and vertically, and time your sub-carrier as well. Humph!!! :evil:

But seriously Gary, please start putting a reference input on ALL of your miniconverters and open gear converters that convert to SDI. When you reclock the SDI, start reclocking it TO a reference input (when available). This would help us all out, and make everything you ever use on a miniconverter a genlockable source.
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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 12:25 am

Ssmith3 wrote:Doggone whipper-snappers! Back in my day, you had to time all of your sources horizontally and vertically, and time your sub-carrier as well. Humph!!! :evil:


I go even FURTHER back when you had to also register the camera's; ie adjust the red and blue H/V centres to match the green!

But nowdays... the only reason you need to genlock the camera's is to sync the vertical or frame start to match the ATEM frame syncronisers. This then prevents the 1 frame latency.

I have been doing this for some time using HDMI to composite converters at the camera end on the camera converter and feeding it into reference in on the camera.

With an ATEM system the ATEM is the master sync source (which can be referenced) so using the ATEM output as a reference would not cause any problems if there is a dodgy input.

If you tried that in the golden analog dayz all hell would break loose!

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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 12:58 am

yes baz, genlocking pre ATEM helps prevent the frame sync delay but its surely not the only reason. *MY* reason for being in time before the switcher is to cut almongst the sources for ISO recording and have clean cuts presentable for replays and later playback. This is PARAMOUNT for every production we do. If you don't genlock then the cuts result in either glitches or long periods of black at the cut points while everything retimes to the new source. You can frame sync before the recorder but the FS1 I would use to fix this problem adds another 3000usd to every recording output feed...genlock is the way in my opinion. And if the 15 million dollar remote trucks do it that way it's a good precedent to follow.

Ssmith I agree with your point about a ref input on the BMD converters. YES it would make life easier for those of us who know what to do with it. And genlocking the ATEM and cameras DOES put everything in sync, as the ATEM frame syncs the inputs AND clocks its outputs to the ref when used. When it's all locked to one ref, you can put everything into a video hub and switch between cams, vtrs, grfx, aux outs, and PGM glitch free. My system NEEDS to do this every show.

And seriously BMD, this new genlock info on the StudioCam is a BIG deal-you should point out this feature in all of your materials. Send the three of us a cut for advertising consults… :lol:

Also, I'm glad to hear that the new switchers embed tally info into the auxes too, my 2ME DOES NOT do this and I rarely need to send PGM as a return. A step in the right direction but the BMD fiber solution has never had much appeal to me. Good thing I'm a fiber guy… :-)

Here's an idea for the masses…I have other routes for intercom so would not use that feature in the new 2ME 4k. BUT! Say you need to send an IFB feed out to talent. Send the IFB audio into the intercom input on the switcher and it will embed into ch 15-16 on the AUX/PGM outs you would use for a return/monitor feed. Extend the camera/converter headphone output for the talent's IFB earpiece, use the camera input to bring the talent mic back…Viola! If BMD would only use ch15 for its one intercom channel and free up ch16 for IFB on a separate input this could be a sweet setup for many…..oh dear there I go again...
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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 4:03 am

Not to mention that some of us have some other brands of switchers as well. Not all switchers have frame syncs (or in ATEM's case, reclockers) on every input. I have an ATEM, but I also have a three other switchers that would benefit from good genlocked converters.

I'm on a university campus. I take in feeds over fiber from other buildings on campus and live switch them. If my BMD Open Gear Optical converters had a tri-level sync genlock on them (even available through the FRAME, not necessarily on a BNC) it would make my world so much easier. I could switch 12 cameras without frame syncs. That would be awesome.

Plus, Gary, there is almost NO ONE who makes fiber or HDMI converters with a genlock/reference on them. This is a good way to be better than everyone else in the field, not just the most affordable. Grass Valley has a converter that will genlock an HDMI or component input, but not one for fiber. And that unit costs about 1000 USD. Or we can run the signal through a proper frame sync for a 2-3 thousand. Or BMD could make what I described and have their "genlockable version" for a little more. You'll sell a ton. Your UpDownCross will do it, so I know you have the capability. I haven't seen anyone that makes a fiber to HDSDI with a TLS input.

And Baz, yeah I've had to set the registration on cameras as well. Good times.
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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 2:29 pm

To all, I am enjoying this conversation. For the "Doggone whipper-snappers", I used to be one but my involvement with sync timing involved round glass objects that glowed and we would often pull them hot rather than turn off the equipment for testing and service.

That said, Ssmith3 is absolutely right in suggesting using a program output for reference is not a good idea to put it simply. However, the ATEMS do not reference to any input and are basically free running devices unless the reference is connected. So the video out (even the aux out) becomes a stable reference clock where we can derive horizontal and vertical timing. If we just used that signal to the camera, the video out would be potentially late with respect to the switcher forcing the frame sync on the input to delay the picture to the next vertical causing a one frame delay. This obviously is not what we want, so the camera does have a genlock timing adjustment allowing us to "advance" the timing a bit allowing the ATEM inputs to use minimal delay compensation. In my day, the sync reference were always advanced for things like cameras and VTRs to allow for any processing to be done and still have the output video arrive on time. No frame syncs then.

To be clear on the Television Studio camera, we send return video back down the fiber to the camera. This video can be viewed on the viewfinder for the camera person. We used to send effects back on this line so they could be lined up prior to putting the camera on air. If you send the Aux output back this line, there is a lot of flexibility in what can be done. Also, this return video contains the tally bit, intercom, as well as the camera control from the ATEM should you be interested. All of our ATEM switchers include this tally bit in SDI. Probably only our Studio Camera and Camera Converter utilize this functionality.

Again, sorry for being lengthy, but I find this interesting and timing is one of my favorite subjects.

Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 7:56 pm

Gary, I'm glad to see BMD finally interacting more often with us-your customer base. So thank you for jumping in so frequently here.

You guys keep talking about H and V timing, like the old analog. Now i'm admittedly I am an audio guru that has added EIC to his card now, but since SDI is a serial stream, the H and V discussions don't apply anymore, correct? The only timing for SDI should be that the bits come at the proper steady interval, and that the streams all running at the same rate start the beginning of the "frame" at the same instant. Or am I missing something?

I will have to try using the return SDI converted to analog to time off of. Thats a brilliant workaround and can't believe I never even tried it. The more I think about it it makes perfect sense and will streamline at least one of my projects. Just need some more toys...
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Re: Ref Video (Genlock) over fiber

PostWed May 14, 2014 8:25 pm

In order to mix two video signals, the exact pixels must match at the mixing point. This is really no different than the analog days. So basically the first pixel must arrive at the mixing point for each source at the same time. I think in terms of vertical and horizontal but it's really the electrical signals must match perfectly in time with each other. In Analog days, we had to time to the nanosecond to get the color right. Today. Digital signals generally have some buffer so the exact timing can be a little off. In the ATEMs, the buffer is one frame so the picture can be off that far and it will be delayed to match up with the reference. Of course these delays can be noticeable. Maybe not one frame but when built up with other system delays, it can be quite visible. I thought about making an analog genlock for other cameras using the fiber SDI return as well. The key is being able to advance the camera enough so it isn't behind the reference signal after processing. If the camera is later, it will be delayed up to the next frame to match up. That's why I think in terms of vertical. Good luck.

Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostThu May 15, 2014 3:35 am

Yes! Thanks, Gary, for participating here. It is always good to see you guys on the forums.

Timing issues are definitely much easier in the digital era — unless you have a problem. Then it is much harder to locate or fix. I was just sorting through some old gear and tossed out several old passive timing delay boxes with the loads of delay switches. Most were made by Allen Avionics. Like this guy:
Image
Been a while since I needed one of those.

Please keep my requests in mind for fiber converters with reference. Pass it on down the R&D line for me. Thanks. And yeah, this has been a good topic. I had fun.
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Re: Ref Video (Genlock) over fiber

PostThu May 15, 2014 3:01 pm

I love it. We used many Allen boxes over the years. I also spent a lot of time cutting coax by the inches in order to time a video signal within a nanosecond. Two degrees per foot (roughly). It was really fun then. Later it was adding full sync generators to VTRs so we could place them exactly in time where we wanted. Passive delays usually caused the chroma level to drop so active DAs with delay were used. Definitely pass along the requests.

Regards, Gary
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Benjamin Higginbotham

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Re: Ref Video (Genlock) over fiber

PostThu May 15, 2014 5:32 pm

So, lets extend this past the Studio Camera then. If I use an ATEM Camera Converter and send program back down the line, will it re-clock the SDI input from the camera at that time and provide sync on the camera converter itself? Or does this apply to the Studio Camera only?

If I'm using non BMD cameras for my live event but utilize the BMD fiber extension products... How do I genlock my cameras and prevent the 1 frame delay? Have a situation coming up where we will need to IMAG (new for us) and every delay point adds up quickly. Want to remove as many as possible ;)

If I take the output of the ATEM Studio Converter in to a Teranex that has been locked to the same reference as the ATEM 2M/E 4K switcher, am I helping at all or is the Teranex also adding a frame delay in its conversion?

Thanks,

Benjamin
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Re: Ref Video (Genlock) over fiber

PostThu May 15, 2014 6:29 pm

I'll let Gary be the definitive answer on this, but I am pretty sure the Teranex adds a frame of delay. Often, any re-clocking will also add a frame of delay.

Furthermore, I think using the SDI return as a reference for a different camera would require an SDI to Analog converter. I have my doubts that once you went from SDI to fiber to SDI to analog conversion that the reference would be worth anything. I don't think it would help you in the slightest, and might even hurt.

For timing purposes, I think of the fiber to SDI conversion as my actual source for the switcher, not the camera. This is much like having a satellite feed where you can't actually reference the camera. You have to frame sync it. That is why having a reference input on the converters would be so handy, then you can time your actual source.

There does exist some audio delay devices out there that will delay the audio by the frame. If you experience noticeable delay in your video, you will need to employ one of these to keep the audio timed to the video. Can't recall who makes them. I think that if you are using embedded audio, the audio should get delayed by the same timing as the video, making everything OK in the end.
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Re: Ref Video (Genlock) over fiber

PostThu May 15, 2014 7:45 pm

Ssmith3 is correct about additional delays. The Teranex will do the same thing that is already inside the ATEM and will only add delay. The only way to minimize the delay is to have the camera video timing hit the switcher at or before the reference timing. If, say the camera video is one line late to the switcher, it will automatically be delayed the rest of the frame to line up which is what you wish to avoid. So, the camera itself must be timed to be ahead of this point. To do this, not only do the cameras need to genlock, they need to be adjustable so they can be advanced. Now, of course, you can't advance video but you can advance timing signals which is what is done inside the camera. Once any camera is outputting video, any changes will only delay the image. I'm sorry if I am stating the obvious.

The return video in our Camera Converter is just SDI video and you can send back any SDI video you wish down this line. In the case of the ATEM, we like to send Program or Aux so the Tally, Intercom, and Camera control signals will go to the camera. For other installations, you can send any stable SDI video and use it for genlock at the camera. If your camera is capable of genlocking to SDI, it may be directly connected. If you can adjust the camera timing at the camera, that will work fine too. If you are generating the genlock video from a sync generator, you can set it to advance slightly before you feed it down the fiber.

Now for the more complicated. If your cameras require a Composite or Sync or Tri Level, you would need something that converts the SDI signal you are feeding back to the camera into the desired signal. It may take a couple of items. We have SDI to Analog which may be a step, providing you can convert this analog to sync or reference. I haven't built this but I'm sure it can be done. I'm sure there are people on this forum that have done that as well. I may do a bit of looking around if I knew what type of sync signals you need but it will take some gear to do it.

To answer a different question, we do have reference on some of our converters as well. This will lock the output to the reference which is pretty much the same thing our switchers will do at the input. This always requires a frame buffer of some sort to accomplish and will always generate some for of video delay up to the maximum of the buffer. This works for many signals, but cameras like to be locked internally so the video coming out is not delayed at all.

I hope I have helped and not said anything incorrect. But it is a good discussion.

Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostSun Aug 17, 2014 12:09 pm

This is all very interesting info, thank you all.

I've always assumed genlock in fiber chains from Sony, Grass Valley, Ikegami, etc, was derived from the return video. But reading this thread it seems that is not the case and it's a novelty idea brought to life with the Blackmagic cameras. So then, how is it traditionally done? Is it separately digitized and muxed together with the comm/tally/rs422 signals?

Trying to wrap my head around the concept of reference sent TO a camera derived from an image that could quite possibly be the camera itself (if that camera if taken live and is what's on PGM) but a few frames later. But then I've always thought of reference just being an indication of when to START drawing the frame, not actually having any time relationship. That is, imagine a row of soldiers marching to a beat. One solider could've waited a few seconds before starting to march. But both soldiers' feet land and lift off the ground at exactly at the same time. So they are "genlocked" even though one has marched 100 steps and the other 104 (camera vs return). So if that is the case, what are those timing advancements that need to be adjusted that Gary speaks of?
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Re: Ref Video (Genlock) over fiber

PostWed Sep 17, 2014 12:22 pm

Great thread here guys, I have a related question,

Has anyone tried to mix camera converters with Fibre mini converters? My thinking is that it would be the same "fibre standard" and all the tally and coms is embedded there should be no loss if the mini converter were used at the ATEM end.
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Re: Ref Video (Genlock) over fiber

PostWed Sep 17, 2014 2:55 pm

Gary Adams wrote:To all, I am enjoying this conversation. For the "Doggone whipper-snappers", I used to be one but my involvement with sync timing involved round glass objects that glowed and we would often pull them hot rather than turn off the equipment for testing and service.
....
Regards, Gary


You aren't talking about vacuum tubes are you?

How about station sync coming from microwave remote trucks and waiting for black between
commercials to return to network sync?
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Re: Ref Video (Genlock) over fiber

PostWed Sep 17, 2014 3:00 pm

Big Azz wrote:Great thread here guys, I have a related question,

Has anyone tried to mix camera converters with Fibre mini converters? My thinking is that it would be the same "fibre standard" and all the tally and coms is embedded there should be no loss if the mini converter were used at the ATEM end.


I think the SFP modules are the same but have not tried interconnecting them.
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Re: Ref Video (Genlock) over fiber

PostSat Jul 29, 2017 9:59 pm

Allright very very old topic But a very good and intresting read.!!

I have Some cams that Indeed need a blackburst or Sync. That said they get there signal from the camera converters. Which takes a few lines for processing and sending Out sdi. This Will not Be pixel to pixel with what the atem sends Out (Reclockers, FPGA in the Camera converter) So there is Some delay and thus not in sync with camera's that are directly connected by cable. Also if using a sdi to analog converter this Will introducé a delay. But not exactly 1 frame. Maybe more maybe less..

This can Be fixed by advancing or slow the sync input on the camera to sync up again So everything is in sync.!!
So far So good. But while back in the analog days if your sync was off you wont get a picture or distorted.. But on the atem you wont see that as the framebuffer Will run on and on... maybe if your timing is slightly off it takes 1 full frame minus a few pixels.. (worst case scenario )

While you can not switch off the framebuffers in the atem.. there is no real way in an atem only system to notish the 1 frame delay... if you had a videohub between it you could check if it does clean switching between sources without glitches. But not everyone has a hub / router between there gear.

So is there any other smart trick to check if all sources are timed well and are relative in sync with the masterclock when using an atem?? And Im not talking About harris scopes to measure input to output delay. A simple methode that can Be done by most of the atem users without to much complicated gear..

Just to check that it does (almost) not use the framebuffer to achive the fastest processing for iMag..

And while i do have answers on most questions on this forum. I do sometimes have questions too. :lol: Really intrested on how my fellow engineers tackle this.
Daniel Wittenaar .:: Xtreemtec Media Productions ::. -= www.xtreemtec.nl =-
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Re: Ref Video (Genlock) over fiber

PostFri Aug 04, 2017 4:15 pm

Hi Daniel. The simplest method I use is loop the camera through the left Smartview (or monitor) and loop the program out through the right Smartview (or identical monitor). Do something in camera like switch color bars on and off while recording the Smartivew with your phone. Some of us can see a frame without the recording method but it helps. It won't easily find sub frame errors, but definitely will show when they are in or out a frame. I have done this with our cameras while changing the line advance. It is important that the camera be a few lines advanced of the switcher.

Regards, Gary
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Re: Ref Video (Genlock) over fiber

PostSat Aug 05, 2017 8:29 am

For sub-frame delays you can visually see the timing offset with a monitor capable of accepting external sync. You should see a vertical and/or horizontal picture shift corresponding to the delay.

Regards,

Dave.
Freelance Television Broadcast Engineer
and Software Programmer.
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Xtreemtec

  • Posts: 1496
  • Joined: Wed Jan 02, 2013 11:48 am
  • Location: The Netherlands

Re: Ref Video (Genlock) over fiber

PostSun Aug 06, 2017 2:31 pm

Gary's methode is smart.. But still takes a lot of time to do 6 cam's in sync.. But oke it is a start.

Dave his methode sounds good.. But looking at all my sdi enabled monitors only my Atomos shogun has a genlock.. I don't think this monitor will help me with that.. But still a good option i think if you have the right monitor. ;)
Daniel Wittenaar .:: Xtreemtec Media Productions ::. -= www.xtreemtec.nl =-
4K OBV, ATEM TVS HD, Production Studio 4K, 2M/E Broadcast Studio 4K, Hyperdeck Studio, SONY FS7 4K, JVC HM700 Full HD Camera

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