The design of this OSD is derived from a need of my client who works in the sector of video services. He had to add titles on video sources PAL/NTSC because the titler in his video camera was very basic.
By the nature of his business, he could not carry any objects other than his laptop, that he used for editing and the video camera. This portable device was battery powered.
The related software for Windows was created in MS Visual C++ MFC with the approach WYSIWYG. With a DB9 RS232 serial port with 2400bps at least used for connection with it, the device was possible to overlay the CVBS signal input with the titles at any desired position on the screen. At that time every laptop had at least one serial RS232 port. 
Initially I worked on the video PAL signals generation with the same microcontroller. After some fun and making a small game like ping-pong , I realized that I needed a specific ASIC to get a decent result with microcontrollers.
I found a dedicated ASIC for my purpose, analyzing the components of a JVC VCR. I discovered the IC STV5730 from SGS-Thomson now ST.
Here you can find the STV5730A Evaluation Guide and STV5730 Datasheet.
The STV5730 is the core of the board and communicates with the microcontroller via SPI.
The IC is available only in SO28 so I had to weld on a DIP socket to be able to experiment.
To test the proper operation of the OSD, I used a small pin-hole camera that generates the CVBS signal input. With this IC when synchronism is not generated from an external source, it is extracted from the input video signal.
If extracted from the input signal, the precision of quartz becomes fundamental.
The quartz must be 17.734MHz for PAL or 14.318MHz for NTSC.
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As you can see, the board there is also an RTC that allows you to view in any location on the input signal, the date and time set. I added this feature when with this board and a video matrix, I made a video surveillance system.
If you’re interested in the code or the schematic, you can contact me. If you want to use this ASIC for a new project, sadly no longer in production. 
A good substitute is that of Maxim ASICs. The MAX7456.
Here you can find its datasheet. MAX7456 Datasheet
I hope it was interesting.
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