![]() ![]() The code for this project is in the example “ClosedCaptions” in the TVout/examples folder. So, how do we capture and decode this data using the Video Experimenter? We need to use the TVout library for Video Experimenter used with all Video Experimenter projects. So, if bits b0-b6 have 4 bits on, then the parity bit is on to achieve an odd number of bits (5). That is, this bit is either on or off in order to keep the total bits in the byte at an odd number. Parity bits are an error detection mechanism. The last bit of each byte b7 is an odd parity bit. That’s right, there are only two characters per video frame, but at 30 frames per second, there is enough bandwidth for closed captions. The next 16 bits represent two 8-bit characters of text. You can see how the voltage rises for the third bit S3. ![]() The 7-peak run-in is followed by 3 start bits with values of 001. The horizontal sync and color burst are just like any other video line, but the section called “clock run-in” is a special sinusoidal wave that allows the TV to synchronize with the closed captioning data which is about to start. This shows the voltage of a composite video signal for line 21. Waveform for the closed caption data on line 21 of a TV frame Here is what the line 21 signal looks like: Whether you are displaying it or not, the data is in the broadcast encoded on line 21 of the video frame. When you activate the closed captioning feature on your TV, your TV decodes the information and displays it on the screen. The data that your TV displays is embedded in the broadcast itself in a special format, and in a special location of the video image. There a lot to learn here, so be patient! First, you can take a look at a video showing this capability, then keep reading to learn how it works. No doubt, you’ve all seen closed captions displayed on a TV, but how does it work? This project will explain how closed captioning technology works and then show you how you can decode and display the data using your Arduino and a Video Experimenter shield. It is typically a transcription of the broadcast audio for the benefit of hearing impaired viewers. Difficulty Level = 8 How Does Closed Captioning Work?Ĭlosed captioning is the technology used to embed text or other information in an NTSC television broadcast (North America, Japan, some of South America). ![]()
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