Hi, Im a VJ situated in Norway and new to this forum.
I have as many fellow VJs a request for a certain bit of hardware: a vga crossfader. As far as I know this apparently simple gadget is only available in expensive videomixers that also come with a lot of other functions that I really do not need.
What I need is: two fully compatible vga inputs, a cross fade between these two signals and one compatible vga output.
Is it possible to make a stand alone mixer like this through the arduino-platform?
Isn't the problem the same as any video mixer - making sure the syncs are locked?
If the syncs aren't locked, you have to buffer at least one frame from one or both sources (this is way beyond what an Arduino is capable of).
I think that's where the expense comes - you effectively need a timebase corrector.
If the sources are already locked, it's relatively simple to mix them.
video requires some fairly specific timing signals to display on a screen, if they are not in sync with eachother when you go to fade the sources the whole thing will scramble
Ok. And other than these signals having to be in sync, what is the main difference between a normal bnc/PAL/NTSC-signal and what comes with VGA? These signals is apparently a lot cheaper to crossfade, probably because they stay PAL/NTSC.
VGA is simpler to cross-fade because the colours and syncs (horizontal and vertical) are already separated.
In a composite signal like NTSC or PAL, you have a colour sub-carrier superimposed on a luminance signal, that also carries the sync information.
However, you still need to have the signals genlocked, that is, the syncs have to be synchronised between sources.
And could you explain to me, in layman's terms, what "locked syncs" is?
A video image consists of a zig zag line going from the top of the screen to the bottom. Sync pulses control when the line goes to the top of the screen and also when the line starts from the left of the screen. If you have two video signals the sync pulses on both the video signals must occur at exactly the same time. That is called sync lock. You can only cross fade if the two video signals are locked.
Now you see why:-
this apparently simple gadget is only available in expensive videomixers
because in reality it is not a simple matter to get two independent video signals to be exactly synchronised.
In a composite signal like NTSC or PAL, you have a colour sub-carrier superimposed on a luminance signal, that also carries the sync information.
And a vga-signal does not have anything like this, which render it impossible to "Lock the sync"?
How do they then make it happen in video mixers like the V8 http://www.fullcompass.com/product/355185.html
(does only have vga inputs, which makes it useless for me. But still: it does fade two different vga-signals)
And a vga-signal does not have anything like this, which render it impossible to "Lock the sync"?
No you can always lock syncs. The fact that one system has colour sub carriers can make it slightly harder.
There are two basic methods, gen locking or frame storage.
To do this you feed a master sync to both video sources and get them to use that. Alternatively you can synchronize one video unit to the syncs of the other. This is sometimes called a gen lock.
The second way is to digitize one of the video signals and store it in memory. At the same time you read out the memory using the sync pulses of the other video signal. This is why they are expensive.
To do this you feed a master sync to both video sources and get them to use that. Alternatively you can synchronize one video unit to the syncs of the other. This is sometimes called a gen lock.
Though it might be hard:
-Is it possible to do this trough the arduino?
No - see replies #1 and #9.
UNLESS - your sources are genlock-capable, in which case, you may just about be able to use an Arduino as a genlock source, though I have my doubts.
It certainly isn't capable of performing as a VGA timebase corrector (TBC)
Post #1 and #9 did not say arduino was unable to genlock, but I get your point. -It can not act as a TBC.
But regarding arduino acting as a genlock source: If Im mixing from two identical computers (macs), should they not be able to resync their signal to this source?
anything is worth a try, as far as them being identical machines, it sorta doesnt matter, they will be using vga standards
I am not 100% sure how vga starts sending the signal, but i am pretty sure your not going to get 2 of anything to be in sync down to 31khz by pushing both power buttons at once and holding your breath
I am not saying its impossible, but its going to take some thinking and your continued persistence on the idea
anything is worth a try, as far as them being identical machines, it sorta doesnt matter, they will be using vga standards
It doesn't matter if they're both the same machine type with identical video adapters, using the same video standard, if they're not synced, it isn't going to work.
They may be running at precisely the same clock speed to the fifth decimal place, but if they start out even a couple of microseconds apart, that's how they'll stay.
The standard 15 pin D-type VGA connector does not have a genlock input. Maybe Apple have done their own implementation.
but if they start out even a couple of microseconds apart, that's how they'll stay.
Well the stability of the crystals will grantee that the two signals will drift over each other continiously.
As stated before you can't gen lock two computers because the circuits haven't been designed to do gen locking. Some TV cameras can be gen locked but not computers.
One solution is to fade on video source to black, switch over to the second source and fade it up from black.
No I won't give up, thanks.