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Jlerch

Do video splitters also buffer?

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Ok, so I did some searching and I did a No-No by y-ing a video cable from one source into two video devices. The 1st device is my Video Goggles (which work fine) and the second device is an AipTek A-HD camera that I normally love, but this is the first time I've tried using it as a DVR.

The problem is the Aiptek Camera, doing duty as a DVR, will stop using an external signal if it loses sync or gets static on in the video feed. Instead of soldiering on, it says to heck with it and stops recording. It took me a few times to figure out WTF?? One minute it worked, the next minute it didn't.

So, To keep the Aiptek camera happy, I'm told I need to feed it a buffered input. Something that will keep the video sync (?) going even during signal drop outs.

For instance, this video shows one anomaly that happened towards the end of the flight. Normally, the DVR would have just stopped recording.. (Shrug)

The other alternative is to find a proper DVR, but the AipTek A-HD Video in feature sure works nice when it works! :-)

James

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No, common splitters/buffers buffer the signal in the way that they have an amplifier that can source enough current to ensure anplitude will be correct, but they don't "buffer" the signal in the way of maintaining sync. Those that do it are pretty pricey professional devices, and you could buy several better recorders before reaching the price of the buffer ;)

Some OSD chips like the MAX7456 can output a sync when they see a sync loss, but they will only do so after several missing syncs so it probably wouldn't help you as there would still be a drop between the time the sync is lost and it starts generating one itself.

Edited by Kilrah

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I have been looking for a gadget to fill in the missing syc pulses for some time without luck, I have even made my own but nothing has been 100% reliable. It seem tape is still the best at recording regardless of feed quality.

Terry

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Nah, recorders that fail that way are really a minority. Most of the solid-state or hard drives recorders I've used work just fine with any kind of dirty signal.

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Not my experience - 2 HD recorders, 2 SD recorders and a couple of miniDV recorders all stop recording after a few seconds of lost signal.

Presumably a 'feature' :D

- but a real pain for FPV. Try before you buy etc...

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All of the HD recorders I have used have made the file unopenable after a few seconds of bad video.

Terry

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Thanks Gents,

I was afraid of that, a splitter is actually a repeater. Garbage in, Garbage out..

So, is anyone using a DVR that works somewhat reliably? I think I'll do better once I get away from all the "Garbage" in my yard and get back out into the open country. The fades will happen less often, so the DVR should keep going.

However, I want to be able to count on the DVR for the time when I put the airframe in. Not having a video to go look at and triangulate off of is going to really "Grind my gears"!

Edited by Jlerch

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The Archos recorders are good. At worst they will drop a couple of seconds of video after a hard video drop making a "jump" when playing back, but they don't stop recording altogether, at least from my experience.

Edited by Kilrah

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Hay Kilrah thats good news , I have just switched over to using an Archos 405 but only have 1 video from it as the internal battery seems to go flat after a few days if not used. I have just made up a 5v psu for it so if this **** wind will go away I can go and test it.

Terry

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Okay, never had such a battery problem here, those I've used would still be full even if not used for several weeks. If it's still new and under warranty I'd return it!

Oh I just remember, check the manual/settings before doing that, usually the new series just go to sleep mode if you turn them off with a short press. A long press or using the "complete shutdown" option in the menu is required for a full power off. There might be something to have it turn off after some time in sleep mode, but I'm not sure.

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Would an Oracle Video Diversity Controller help me any? IE, will it still drop Vsync as it switches sources?

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None of the recorders I've tried had problems from the Oracle switching, just prolonged white-outs (when neither receiver had a good signal).

I must try an Archos. Which was the last model to take AV IN without needing a docking station?

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I think it was the AV5x0/700. I have an AV700 personally, got it at a sale of display models at a store here for about $200. It takes a 15$ adapter to connect to the video input, but it's already a lot less than the travel adapters of the newer series. None have ever had a direct video in from what I remember.

Edited by Kilrah

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I found the Cowon A3 does a very good job with the video downlink recording. It will continue to record when there is no transmit signal received at all. I wish other recorders would continue to record without a signal but few do. I have an HD PVR (Hauppauge) unit that I would love to use for video recording of the downlink but it also fails when sync is lost. It sure would be nice to find a device to maintain sync at the receiver when the downlink drops out.

OMM

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Would a Time Base Corrector keep the Sync going ? If so that is only just over 200 dollars, and would open up a whole new world of recorders for us... It would be worth the price.

Mike

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Would a Time Base Corrector keep the Sync going ?

Sync fly-wheeling is a feature on some TBC's, but not all. Besides being able to fix poor/missing syncs, some TBC's offer drop out compensation to restore very short periods of missing video (either with h-line or frame buffering). However, these sort of things are extra features that are not necessarily included in any particular TBC.

Keep in mind that TBC's were targeted for tape based VCR applications and our wireless video application would be a hardship use for them. Honestly, our video signals become a serious mess at times (certainly messier than a typical analog video tape would present). Long story short, you would probably have to try several different commercial TBC's before you found the magic one (if that is even possible). Plus, the best ones are often 19" rack mounted monsters.

My gut feeling is that a commercial TBC is not going to be practical. I propose that someone carefully define what is needed so that the brainiacs on the forums can create a solution. Although it may seem obvious to some that have the issue, it is really not clear to me what is essential. Also, each video device {that has difficulties dealing with poor video} has its own peculiar level of tolerance to the problem. So, that needs to be defined too.

For example, is the goal to simply create substitute syncs (without regard to the video image) as a way to prevent a DVR from crashing when the video signal is corrupted? Or, is the goal to restore the video image (perhaps to prevent blue screen) when the signal is bad? These are totally different solutions, with the latter being quite difficult without a very sophisticated design.

Also, a number of TFT, LCD, and DVR users would need to provide full details on exactly how much corrupted video can be tolerated before their device gets fussy. For example, if this is a DVR crash issue, does it take a sustained loss of video to cause the problem? If so, how many milliseconds of loss is needed to cause it? If it crashes with very short burst of video corruption, then careful details to that are needed. Because each video device will have its own particular level of tolerance, this a tough issue to easily characterize.

By the way, I recall reading on rcgroups that the Aiptek MPVR DVR will act as a realtime video signal restorer. I don't have a link, but the discussion should be easy to find over there. If this is true, then the problem is solved. Seems to good to be true, but certainly possible.

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Hey Thomas YOU are the best video brainiac I know :)

I have tried a few recorders over the years and I have found its not the time the video is lost for but something else. If I had an anti crash gadget last year I would have found the plane I lost for sure, the video crashed the file and made the whole of it unplayable.

For me the flywheel effect idea is great, I'm sure it would work well. I don't mind it cutting in a bit too often with a blue screen or whatever as long as it stops the crashes.

Your Oracle must already do part of the job by sensing video loss so adding the flywheel should be within reach ???

Terry

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It all depends what the recorder crashes on. It might just be the sync pulses, in which case it would be reasonably easy to do (the current Oracle hardware would need mods AFAIK as it can only do passive sync sensing, and switch from one input to another but its processor can't act directly on the signal itself), but if the recorder for example needs the color burst to be there, that would be a whole other complexity to fake.

That's why Thomas mentions that we'd need to first assess what causes trouble.

Or, redo a whole new signal (video ADC chip -> RAM buffer -> video DAC with appropriate control logic to sense video loss and do something like repeat the last good frame or insert dummy image (bluescreen), making sure the output is a fully valid video signal at any time. But that's also some heavy development.

I see AVT indeed has something that looks like the latter (http://www.avtoolbox.com/avt8710.shtml), but to know whether it works in our conditions and not only in VCR-like signal faults someone would have to just try it. Personally spitting $270 to make a $100-200 recorder work, with an added piece of equipment to carry, wire and power isn't interesting. Just get a $400 recorder that works, it will be much easier.

Edited by Kilrah

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I understand where your comming from but there must be a lot of guys that have good recorders they are happy with and would jump at a gadget to make them work for FPV recording. I have a great recorder that uses low compression and so gives a far better picture when interference is pressent compared to any of the mp4 recorders but it crashes unpredictably when fed poor video.

I have no way of knowing what causes it to crash though.

Terry

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I've seen a few posts where the main complaint was that the video glasses intermittently go to blue screen on poor RF signals and the brief loss of image causes a bit of pilot panic during FPV. To make the glasses show a snowy (but useful) image like we see with analog TV displays would be a totally different level of complexity (and perhaps too expensive for a practical solution for us).

Your Oracle must already do part of the job by sensing video loss so adding the flywheel should be within reach ???

You are correct, the Oracle hardware has most of the elements to do this, but not all. If I were to start up a project to find a cure, I'd certainly use it as a breadboard for a crude prototype.

I have no way of knowing what causes it to crash though.

Whoever attempts to solve this will need some data from the existing users. You may not know why it crashes, but you could certainly poke sticks at the video signal to help characterize the DVR's behavior so that a developer can determine what needs to be done.

It all depends what the recorder crashes on.

That is what makes this such an uncertain solution. My gut feeling is that some DVR models will be easy to make happy and other models will be too fussy to find an affordable cure. That is why it is important to collect some data from existing users.

The irony of all this is that the problem is really just a firmware bug in the DVR and in a perfect world that is where the fix should be made. Until the manufacturer listens to their customers, the only solution is to hack onto the video signal and do it externally.

But I have to ask: Would enough people want to pay $75 - $125 for something that just keeps a DVR from dropping out of record mode? I just don't think the interest is there yet to justify a low volume commercially made solution. But there are a lot of hobbyists that have the talent to design and sell this at a bargain price; that is where it might make the most sense.

Lastly, has anyone tried the Aiptek MPVR to see if it solve the problem, as reported elsewhere? I don't mean to use it as the DVR, but instead use it as sort of a realtime TBC for your DVR. If it can really to this then the search is over.

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Hmm I wonder about the MPVR, because from what I remember it only has a single AV jack that serves both as input and output, so don't see how it could be used as pass-through...

I think I have one somewhere, I'll check next week if I remember when I'm at the workshop.

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I have a four year old Aiptek MPVR (model DZ0-V38) and mine has a separate TV out and A/V in. It does indeed offer pass-thru video. However, I don't have one of the fussy DVR's to try, so I have no idea if it is the Holy Grail solution everyone is looking for.

Update: It's a miracle. The MPVR has video genlocking and sync fly-wheeling on the pass-thru port. Or so my o-scope shows. This may indeed be the answer for some fussy DVR's. :)

photo-mpvr-1_02.jpg

Edited by Mr.RC-Cam
It just might work!

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It works with Archos recorders too. BUT, you get the Archos' overlay (when chosen to display), and some noticeable quality drop (digitalised, resized to 640x480, then output again).

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Do you get full video quality using the pass through ?

Not that I can find one availible in the UK to try.

Terry

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From my quick bench tests, the NTSC pass-thru video looks decent; I just don't have the time to make any serious bandwidth measurements. So I'll leave the final judgement up to the those that try it with their fussy DVR.

There seems to be a tiny amount of processing delay, but hardly noticeable. I would guess a couple of video frames worth. Also, I didn't have time to confirm if the framerate is reduced (doubt it would, but anything is possible).

FWIW, all my pass-thru tests were with the MPVR idle (not recording any video). I don't know if it acts differently if the record mode is turned on.

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