The text contained in captions generally falls into one of three categories. Subtitles: Rendered in a graphical format and overlaid onto the video / film. In the NTSC system, it’s often referred to as Line 21, since it was transmitted on video line number 21 in the Vertical Blanking Interval (VBI). Usually they can be enabled or disabled by the user. I often use the word captioning which encompasses both closed captions and subtitles: Closed Captions: Transmitted in a non-visible manner as textual data. I may have been the last engineer working with analog captioning as everyone else moved on to digital.īut before digging in, there is a lot of confusing and imprecise language floating around on this topic. Back in the early 2000s, I unexpectedly found myself involved in a variety of closed captioning projects, both designing hardware and consulting with engineering teams at various consumer electronics manufacturers. In fact, it was quite a struggle for captioning to become commonplace. Thanks for the tip! Posted in home entertainment hacks, Software Hacks Tagged ceefax, raspberry pi, teletextĬlosed captioning on television and subtitles on DVD, Blu-ray, and streaming media are taken for granted today. We like this project a lot, because while it’s not the first Pi teletext system we’ve encountered, the use of a scraped live feed makes it one of the most creative. Behind it all is a Raspberry Pi, with a vbit-pi board injecting the teletext signal onto the video, and raspi-teletext creating the pages from source material derived from a set of custom scraper scripts. He shares with us the story of how he arrived at a teletext service, before writing code to scrape the BBC news and weather websites and populate his modern-day CEEFAX. He has a particular enthusiasm for analog TV, and as such has his own in-house channel served by a UHF modulator. It went the way of the dinosaur with the demise of analog TV, but for the flame is kept alive with his own private version of the BBC’s CEEFAX service. Teletext was an electronic viewdata information service digitally encoded in the frame blanking period, and a TV set with a decoder chip would provide access to many pages of news and other services all displayed in the characteristic brightly colored block graphics. As analogue TV slides from memory, there’s a facet of it that’s fondly remembered by a band of enthusiasts.
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