Trying to do something a bit unusual with SD video ?

[Ice Coffee]

I am trying to combine 2 video signals using a 50/50 vertical split, I will try to elaborate.

Signal A [_|X]
Signal B [X|_]

Combined Output signal [_|_]

as you can see I have cropped off the right half of Signal A (represented by the X) and the left half Signal B and then combined the 2 to make the resulting output signal.

So far I have worked out I can do half of it using a dac decoder chip, infact this
TVP5150AM1 from texas instruments has an AVID feature the will allow me to crop each picture to the 50% I need, I will then need an adc encoder chip as the resulting signal from dac is in Y,cb,cr digital format, but combining the 2 images into one is not clear to me ! if the sync pulses were tied together I could use some fast video switching to switch between the two resulting images without any tearing, but that sounds like a cheap hack to me, any input is much appreciated.


Thanks in advance

Ice

 

[55pilot]

Unless the two video sources are PERFECTLY synchronized, you can not just switch between the two sources in the middle of the line, or even in the middle of the frame. The chances of two independent video streams being synchronized are zero.

The only way you can do what you want to do is using a "frame grabber." You have to digitize the two video streams, write the digital data into a memory buffer and then generate the combined video from that buffer. It is pretty standard stuff, but it is definitely not a hobbyist level design.

---55p

 

[Ice Coffee]

Your comments are much appreciated, in answer to your sync statement yes the 2 video sources will be perfectly synchronously timed, infact it will be using 2 channels on the same ADC decoder clocked from the same xtal.
Without going into to much detail the whole point of this is to replace an aging system which does the exact same thing but requires a pair of cameras with sync outputs which have their sync pulse's aligned on a scope first (via a h-phase adj on the camera) before the video and sync is plugged into a combiner unit !

PS please elaborate on this frame grabber design, I am already converting the video into a CCIR 656 stream, if I could make up this intermediate frame grabber circuit I could combine the images before I pass it onto the ADC encoder.

this is what im thinking as a block diagram

Decoder ---->Frame grabber/Combiner------> Encoder !

 

[55pilot]

The video sources need to be synchronized. That means that either the two cameras have to be running form the same reference clock and some kind of synchronizing pulse, or one of the two cameras has to look at the other's syncs and synchronize itself to it. A cruder way is to synchronize the two by tweaking the h-phase while looking at the two on a scope, but they are not going to stay synchronized for long and will loose it if the temperature changes much.

Think of it has two people singing the same song and your wanting to switch between the two every second. The only way the result is going to come out sounding decent is if both are using EXACTLY the same music. Otherwise if one gets ahead of the other by half a second, the result is going to be noise.

Doing and synchronizing the ADCs is not going to do anything. It is the sources that have to be synchronized.

To do this digitally, you need to use a circuit called a frame grabber. It saves a video stream to a region of memory. If you have two of them, you can take half a frame from one source and half a frame from another source and make a combined video in any form you like. You can learn more about frame grabbers using google.

A frame grabber is definitely not a hobbyist design project. What are your capabilities and resources?

---55p