I've implemented this circuit in both analog and digital. Perhaps you could elaborate on the requirements ... if you're the OP.
You don't need an MC1378 do do this analog. If you could buy it, it's not all you would need. You could generate your timing overlay in an FPGA that was synchronized to the Hz scan rate, then use a multiplier for the cookie cutter, as one of the other posters suggested.
More detail on the application is required for smarter discussion on the options ;->
Frank
The major requirement is that there will be overlayed some counters (frame counter, current time and some measurement informatino) on each frame, there can not be any glitches in this so that the frame counter stays the same for two whole frames for example. Other than that, the requirements are that the circuit must be able to process a CVBS signal, either PAL or NTSC provided through a bnc- connector - overlay the signal and then generate a CVBS signal(the same standard as the input) on another bnc-connector. Functional requirements are possibilities for graphical content generation(i.e. graphical menus, sizable fonts etc.).
I guess the most important aspect of it is reliability in that it does not "drop" any frames.
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As another poster pointed out, if I were to take the FPGA route, I would use both a digital encoder and decoder that performs all the sampling and provide a 4:2:2 BT656-stream to my logic.
Best regards, Andreas Erikss>
I'm not the OP but I am working to a similar set of requirements. I need to overlay text and graphic color symbology over composite video. I have much experience with digital video processing and understand how to genlock the overlay video to the incoming video. I'm not sure how to ensure that the color burst or color subcarrier is locked between the incoming video and the overlay video. This part is where I though that the MC1378 would be useful.
My desire is to create the properly synchronized overlay video digitally and then use a standard composite video encoder circuit to generate the overlay video to be switched in using an analog multiplier. However, I'm not sure how to force the overlay video encoder subcarrier to match the incoming video. I saw your earlier post regarding the need to insert the right chroma phase. I am aware of the need but don't understand the implementation.
-- David
Regardless of whether you intend to decode the input signal to YCrCb (or even to RGB) or keep it as CVBS, you'll need an oscillator for the chroma subcarrier which is synchronised to the colour burst on the back porch.
If you plan to decode to YCrCb, you need the oscillator to demodulate the chroma signal into Cr and Cb. If you plan on keeping the source signal as CVBS, you need the oscillator to generate the overlay's chroma signal from its Cr and Cb.
The general principle is to first generate a "gate" pulse which identifies when the colour burst is present, then while the gate is open, synchronise the oscillator to the burst using a phased-locked loop. The rest of the time, the oscillator runs freely. The frequency needs to be close enough that the phase doesn't drift significantly over the period of a line.
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