Seamless Video Switcher

[cne]

Hello,

I have tried to make video switchers in the past with switches, but they create allot of noise. I was wondering if there is a way to make a video switcher so it is seamless, one camera cuts to another without any noise. I need to switch 4 cameras using composite video, and I do not need to switch audio.

Thanks,
Cameron

 

[crutschow]

You could use a video switch such as from **broken link removed**. If you control these with a mechanical switch, you will need to debounce the switch to provide a smooth transition from one signal to the next.

 

[Nigel Goodwin]

It's not a question of 'switching', to be seamless all sources need to in exact syncronisation.

 

[mbarazeen]

see the bellow link

https://www.electro-tech-online.com/threads/channel-selector-project.105567/

 

[crutschow]

It's not a question of 'switching', to be seamless all sources need to in exact syncronisation.

Since he was talking about "noise" I assumed that was from the switch bounce. But you are certainly correct, that for seamless switching, all video sources must operate from the same sync.

 

[crutschow]

see the bellow link

https://www.electro-tech-online.com/threads/channel-selector-project.105567/

That's for an audio switch, not video.

 

[cne]

Since he was talking about "noise" I assumed that was from the switch bounce. But you are certainly correct, that for seamless switching, all video sources must operate from the same sync.

Yes,
In my previous switches, when the camera angle was switched, there was a short period of "noise" between the transition. What I want to have is a clean transition. For example: at a live sporting event, when the angle is changed you hardly notice the transistion.

 

[cne]

Sorry, I accidentily posted the same message twice.

 

[mbarazeen]

That's for an audio switch, not video.

it will work for both audio and video. i have built and used such a switch long before. it worked like seamless.
if he want sync then have to use TBC (time base correctors) to make sysc then feed it to the switcher.

 

[cne]

How would I go about putting the inputs in sync?

 

[crutschow]

How would I go about putting the inputs in sync?

First you need cameras that can be synced together. Then you need a sync generator.

 

[mbarazeen]

why don't you try the switch 1st, i believe your real problem was with switching not with sync

 

[Nigel Goodwin]

why don't you try the switch 1st, i believe your real problem was with switching not with sync

I would certainly disagree with you, and I suspect everyone else would as well. Unless the sources are synced together, there will always be a noticiable change when you switch.

 

[Oznog]

Nigel's right. There's no way you can switch seamlessly. If one signal is 1/4 the way through the first field of the interlaced frame, and then you switch to another signal which is 3/4 way through the second field, well, there's no way a TV can handle that! And it may take several frames to lock onto the new signal for all I know, it's gonna be hardware-dependent. A TV and VCR will react differently. A 1990's TV set and a 2007 TV set and a plasma screen TV set will react differently.

AFAIK, the news stations fixed that by either running very special cameras with a single sync signal, or use a digital frame buffer to match up two dissimilar signals at the moment they switch. Without a common sync signal though, 2 sources won't even maintain the same phase relationship, they'll drift apart since one will always run faster than another.

 

[imix500]

Yes, it's called genlock.

 

[imix500]

There are switchers out there that correct the sync issues by creating new sync signals internally. They are often prohibitively expense though.

 

[Wade Hassler]

have you considered:
Separate the sync from the composite video and pass the video through an analog switch.
Recombine video and sync on the far side of this switch and send the composite video through the main switch
At the time of source-switching, blank the video for a period of time, say 2 frames, that will guarantee
no visible synchronization problem

 

[cne]

have you considered:
Separate the sync from the composite video and pass the video through an analog switch.
Recombine video and sync on the far side of this switch and send the composite video through the main switch
At the time of source-switching, blank the video for a period of time, say 2 frames, that will guarantee
no visible synchronization problem

Sorry,

I am just a little confused as how to build a circuit to do the above.

Cameron

 

[cne]

Also, how do you change the sync of video signals?

Cameron

 

[crutschow]

Also, how do you change the sync of video signals?

Cameron

You can't, unless you have a video delay storage circuit that can delay each video source signal and then resynchronize them to the same frame sync. Otherwise you have to synchronize all cameras to the same sync source.