Thank you for making me feel old today, @TechConnectify, by telling me that #DVD will turn 30 next year...
But more importantly, thanks for your interesting video about #ClosedCaptions and #subtitles in that format, and how a lot of modern HDMI implementations of it are no longer supporting #line21 CC data: https://youtu.be/OSCOQ6vnLwU

History of Closed Captions: Entering the Digital Era

When you want to read what is being said on a television program, movie, or video you turn on the captions. Looking under the hood to see how this text is delivered is a fascinating story that stared with a technology called Closed Captions, and extended into another called Subtitles (which is arguably the older technology).

I covered the difference between the two, and their backstory, in my previous article on the analog era of closed captions. Today I want to jump into another fascinating chapter of the story: what happened to closed captions as the digital age took over? From peculiar implementations on disc media to esoteric decoding hardware and a baffling quirk of HDMI, it's a fantastic story.

There were some great questions in the comments section from last time, hopefully I have answered most of these here. Let's start with some of the off-label uses of closed captioning and Vertical Blanking Interval (VBI) data.

Unintended Uses of VBI Data

While I was immersed in the world of VBI data and closed captions for several years, I kept discovering applications that were not related to the intended use.

Newsroom channel monitors

Back in the day, I discovered a small company called SoftTouch, Inc., "innovators in the obsolete" according to owner Doug Byrd. They made various niche market CC products, and in fact, I still have several of his products today. Most prized are two CCEPlus line 21 generator cards, the only full-length ISA cards I've ever owned, which have given me an excuse to keep a fully working Gateway 2000 486DX2-66V in my lab for over 15 years.

Full Length ISA Card Closed Caption Decoder

I enjoyed my phone calls with Doug over the years. He is quite a character, a great story teller, and I learned a lot about the captioning industry from him. While his niche products were used in all kinds of systems, one that sticks in my mind is in news rooms. Imagine a system designed to monitor a wall of televisions (or just tuners) equipped with CC decoders feeding the RS-232 text to a computer which is programmed to look for various key words and alert the staff when found. In fact, we wrote about a similar project on Hackaday about ten years ago.

Real-time translating from Spanish

Popowich and McFetridge at Simon Fraser in 1998

One surprising application I stumbled upon was a small set top box designed to translate the English dialogue for Spanish speakers who liked to watch US daytime soap operas. This was an interesting project on two fronts. Researchers Fred Popowich and Paul McFetridge at Simon Fraser University developed a "shake and bake" machine translation algorithm which could be implemented in hardware of the day. It was about 80% accurate, but they discovered something interesting. Eighty percent worked just fine for people who only spoke Spanish, but bilingual speakers were annoyed by the mistakes.

Dictionary lookups from DVD captioning

I was discussing closed captioning and DVD subtitles with some Korean engineer friends one night over soju, and learned there was a Korean company who made a specialized DVD player. What made this player special was it had a built-in OCR engine to read the subtitles (not the captions) and offer translations and definitions to the user -- it was intended as a language educational product. It did not do real-time OCR translations, instead doing the OCR when the user pressed PAUSE in order to query the machine for help.

Weather radar data distribution

While teletext was primarily used in Europe, the WST standard included a variation for NTSC countries -- The North American Broadcast Teletext Specification (NABTS) known also as EIA-516. Both CBS and NBC experimented with teletext service, but it wasn't popular. However, the data broadcasting ability did find some traction in other ways. I discovered one surprising application while learning about VBI signals back in the early 2000s. I was talking to an engineer at a local weather radar company in the US, and found out they were broadcasting weather data and radar images over the VBI for the benefit of various emergency preparedness groups. He even lent me an NABTS receiver which I installed in my PC and could monitor the real time data from my desk. To my surprise, he told me that television stations were renting out the VBI lines. In crowded markets like New York City, for example, there might not even be any empty lines available.

Datacasting Weather Radar Data over the VBI

Financial Data

Electra Teletext Sample

It wasn't just the weather radar data folks using the VBI, either. A number of datacasting services sprang up which used the VBI to distribute financial information such as stock and commodity prices. Several networks were in operation, some since the late 1970s. They included DTN Real Time, Electra, and Tempo Text. By the mid 1990s, all these services had shut down, the internet having taken over the role of time-sensitive datacaster.

VBI Data Receiver

Extended Data Services

The closed caption standard was eventually amended to include what's called extended data services, or XDS. This auxiliary data was carried in the field 2 VBI and included information like time of day, V-chip rating, station ID, and basic programming information. Some early electronic program guides (EPGs) like Guide Plus were sent over the VBI. There was also an emergency alerts portion of the XDS, which could announce all kinds of weather and other emergencies, down to the state and county region, and for a specified duration.

Making a Line 21 Decoder Today

As I mentioned in my article on analog closed captions, making an analog closed caption decoder in the 21st century is best done without relying on specialized all-in-one ICs. There are three functions required in such a receiver:

• Syncing to the video signal
• Slicing / thresholding the data
• Processing the protocol

Surprisingly, syncing to the incoming video was a real challenge. It was because of the Macrovision copy protection scheme. Wild pulses are inserted in the VBI, ostensibly to prevent making a tape recording (these pulses mess up the VCR's AGC circuitry). Of course, people who want to make copies just built or bought a Macrovision suppression box. But if you want to reliably sync to Macrovision-ladened video, it's not simple.

I considered making my own, but there are a lot of special cases. There were also some legal considerations at play, but I was in touch with the Macrovision engineers and wasn't too worried about that. In the end, I went with a sync separator that was Macrovision tolerant, and had been designed and tested to work in a much wider variety of Macrovision scenarios than I could hope to reproduce in my testing.

Build Your Own CC Decoder Project

There are various ways to slice the line 21 data. I successfully built several boards based upon a clever open source project. Richard Ottosen and Eric Smith published a nice design using a Microchip PIC16F628, which was subsequently expanded on by Kevin Timmerman. These designs make good use of the PIC's internal comparators: one as a peak detector and the other for data thresholding. Check these out if you are interested in making your own decoder.

Processing the data once you get it from the decoder can be hairy, depending on how accurate you want your design to be. Reader [unwiredben] commented on the previous article how fun it was to recently write a ground-up implementation. I wholeheartedly agree. One issue is that the requirements are spread out among various documents. Some of them were almost unobtainable back in the year 2000, and yet they make up the official, legal requirements expressed in the FCC regulations.

I particularly remember having a very tough time getting a required report from PBS and another from the National Captioning Institute. It wasn't because they weren't cooperative, but because the reports were so old they couldn't find them. (I eventually got the reports, and also a real Telecaption II caption decoder on which many of the final specifications were based.)

Telecaption II External Decoder Box

One incident I recall is trying to buy a set of CC verification tapes. Supposedly they were available from WGBH Boston, but when I called it seemed that nobody had asked for them in years, and they weren't sure any existed anymore. They eventually found one remaining set and shipped it to me here in Korea, where it almost got destroyed in customs due to some obscure law prohibiting the import of prerecorded media. One point to consider -- if you simply want to extract text for analysis, the processing will be a lot easier than if you also want to properly display and position the text on-screen.

It is possible to build a digital CEA-708 (see below) decoder. If this is something you're interested in,

The Making of Captions

The process of making the caption text is too complicated to cover here. In brief, the dialogue has to be transcribed into digital format. In the case of real-time captions like for news or sporting events, techniques, skills, and equipment have been brought over from the world of court reporters. In the case of pre-recorded programs, the process can be aided by scripts. But they still have to be checked against what was really said by the actors. Next, any additional cues are added, and then the dialogue has to be broken up into chunks which need to be correctly positioned on-screen and timed with the audio track.

If you're interested in learning more about this, check out Gary Robson's website. Not only does he discusses the process of making captions, but Gary has been in the caption industry for a long time and written several excellent books on the subject. I've read all of them and sought his advice on a few occasions -- a very nice and knowledgeable guy.

Captions and Digital Video

So far the focus has been on analog closed captioning which was used for over-the-air broadcasting, and more or less for cable television broadcasts as well. But what about other ways we view programs? In the case of VHS tapes, it was fortunate, if not anticipated by the designers, that line 21 signals could easily be recorded and played back by videotape equipment. Then along comes digital video in formats like Laser Disc, DVDs, Blu-ray Discs, and streaming, and the world of captioning falls apart -- for awhile, at least.

Transition to Digital

First we have the Laser Disc. They stored and played back captions in both NTSC and PAL formats. No big issues here, but just wait. Next comes the Digital Versatile Disc (DVD), and things begin to get murky for closed captioning -- a situation that persists more or less to this day with DVD and Blu-ray Discs (BD). The DVD specification calls out a user data packet specifically to store the digital pairs of caption data (as digital data, not encoded in a video line). Although I'm not aware of any technical reason why a PAL DVD couldn't do the same, only Region 1 (North America) NTSC discs can store the caption data and still be compliant with the specifications.

Most DVD players use this data to generate an analog line 21 signal on the video output signal(s), which can then be decoded by your TV set's internal CC decoder under viewer control.

• Composite video output
• S-Video output:
  • on the Y/Luma signal
• Component video output:
  • on the Green/Sync signal if RGB
  • on the Y-channel if Y/Pb/Pr

There are a very few players that can actually decode the caption data and overlay this onto the output video as open captions, but these players are the exception rather than the norm.

We Have a Problem…

You may see where this is leading -- there is a hidden assumption with Line 21 closed captions. By definition, they are only defined to exist on interlaced standard definition video (480i in the case of NTSC). While there is no technical reason not to, there isn't any agreed upon standard to send the data over the VBI for any other video timing. Nobody thought about it back in the 1970s.

This led to upset consumers who purchased HD televisions and DVD or BD players, only to find out that they couldn't view the closed caption data unless they watched the program in 480i mode. But still, if you use closed captions, live within NTSC DVD Region 1, and are content to watch programming in 480i standard mode. Everything is good? Not quite.

For some reason I still don't understand, not all pre-recorded DVDs contained closed captions, even if captions existed for the movie and were available on VHS tape releases by the same studio. This seemed to be random with one exception -- Universal Studio DVDs never had closed captions. Don't worry, DVD technology offered a "new" solution to this problem -- subtitles. Remember those from the early 1900s?

Because everything was now digital, DVDs and BDs could offer the old style hard-baked subtitles, but with a twist. The user could turn them on and off, and could often select from a wider variety of languages (CC was typically limited to two languages, if that, and those from a narrow choice of languages). The freedom to design subtitles was almost boundless -- as they were just pictures with a transparent background, they could contain anything. It wasn't uncommon to see both English and English CC subtitles on some discs.

Despite lots of sources claiming the contrary, BD discs can and do carry line 21 captioning. I have used BD and BD players for testing line 21 signals over the past ten years with no issues. But the catch is the same as with with DVD, they are only generated at 480i standard definition analog outputs. And the dearth of captioned discs is even worse than DVD -- I would estimate that less than one third of BDs have captioning. I mentioned above very few DVDs have internal CC decoders. I don't think I've ever seen a BD player with one.

Digital Television

The industry working group responsible for closed caption standards realized something needed to be done to bring captioning into the digital era. The group developed a new version of closed captioning, addressing many of the concerns of the community of analog captioning users. Recall that the analog standard was EIA-608. The new standard is called CEA-708 (CEA was spun out of the EIA when it closed down in 2011). Some features that were added, aside from a format that was compatible with ATSC digital broadcasting, include:

• true multi-language support
• different font sizes
• different font styles
• can be repositioned on-screen
• legacy EIA-608 capability

As digital television broadcasts became the norm, TV sets were replaced with those capable of decoding the new 708 style captions. Your TV set probably has this ability today.

Baseband Digital Video and Captions

The quality of our TV and monitor displays increased rapidly. HD analog component signals were soon replaced by high speed, digital differential signalling. Various standards exist, but HDMI has become the de-facto digital video interface for consumer video. Our television sets are receiving HD digital programming and are able to decode and display new style captions. All is right with the world. Well, not so fast.

One would surely expect a brand new standard such as HDMI, designed from the ground up to support all current and conceivable kinds of communications between consumer A/V devices, to handle the trivial bandwidth and format of the closed captioning signal. Well, you'd be disappointed -- somebody did not get the memo. From the start, HDMI has not carried the closed captioning signal. One could be forgiven for thinking it was an intentional decision, as the standard has been updated numerous times and HDMI cables still can't carry closed captioning.

The explanation from the industry was that with change to digital meant that caption decoding must now be performed in your set-top box. This might not have been too bad of a choice if these boxes also provided an ATSC-modulated RF channel output with EIA-708 captions, akin to the Ch 2/3 outputs of old computers and VHS players. As it is, consumers who rely on closed captions now have two or more decoders to fool with: one in the TV's HD digital receiver, one in a cable set-top box, and perhaps a third in their DVD/BD player.

FCC Saves the Day?

With the shift from prerecorded media to streaming, the situation really got out of hand. The FCC stepped in and solved the situation, kind of. You might think that with a well established, existing standard like EIA-708, something already being used in TV sets and mandated by the FCC for all broadcasters, the reasonable answer would be to require streaming services to use EIA-708 also. And maybe encourage the HDMI organization to carry closed captioning information as well. Alas, that was not the decision. Instead, the FCC ruled that streaming services can use any captioning technology standard they wish, as long as they can deliver captions.

I feel that this state of affairs is less than ideal. Looking back at all the neat and unintended uses of analog closed captions, I wonder how many novel innovations are we missing out on by this lack of a uniform captioning standard. Or rather, our intentional decision not to apply the existing captioning standard uniformly. That said, I don't want my grumbling about technical details to distract us from the big picture here. The true goal of these regulations, providing captions to the deaf and hard of hearing community, is being applied across all methods of program delivery. That's wonderful, indeed.

#hackadaycolumns #history #originalart #videohacks #bd #closedcaptions #dvd #eia608 #eia708 #laserdisc #line21

History of Closed Captions: The Analog Era

Closed captioning on television and subtitles on DVD, Blu-ray, and streaming media are taken for granted today. But it wasn't always so. In fact, it was quite a struggle for captioning to become commonplace. 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. I may have been the last engineer working with analog captioning as everyone else moved on to digital.

But before digging in, there is a lot of confusing and imprecise language floating around on this topic. Let's establish some definitions. I often use the word captioning which encompasses both closed captions and subtitles:

**Closed Captions:** Transmitted in a non-visible manner as textual data. Usually they can be enabled or disabled by the user. 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). **Subtitles:** Rendered in a graphical format and overlaid onto the video / film. Usually they cannot be turned off. Also called open or hard captions.

The text contained in captions generally falls into one of three categories. Pure dialogue (nothing more) is often the style of captioning you see in subtitles on a DVD or Blu-ray. Ordinary captioning includes the dialogue, but with the addition of occasional cues for music or a non-visible event (a doorbell ringing, for example). Finally, "Subtitles for the Deaf or Hard-of-hearing" (SDH) is a more verbose style that adds even more descriptive information about the program, including the speaker's name, off-camera events, etc.

Roughly speaking, closed captions are targeting the deaf and hard of hearing audience. Subtitles are targeting an audience who can hear the program but want to view the dialogue for some reason, like understanding a foreign movie or learning a new language.

Titles Before Talkies

Intertitles from the 1920 film The Cabinet of Dr Caligari

Subtitles are as old as movies themselves. Since the first movies didn't have sound, they used what are now called intertitles to convey dialogue and expository information. These were full-screens of text inserted (not overlaid) into the film at appropriate places. Some attempts were made at overlaying the subtitles which used a second projector and glass slides of text which were manually switched out by the projectionist, hopefully in synchronization with the dialogue. One forward-thinking but overlooked inventor experimented with comic book dialogue balloons which appeared next to the actor who was speaking. These techniques also made distribution of a film to other countries a relatively painless affair -- only the intertitles had to be translated.

This changed with the arrival of "talkies" in the late 1920s. Now there was no need for intertitles since you could hear the dialogue. But translations for foreign audiences were still desired, and various time-consuming optical and chemical processes were used to generate the kind of subtitles we think of today. But there were no subtitles for local audiences -- no doubt to the irritation of deaf and hard-of-hearing patrons who had been equally enjoying the movies alongside hearing persons for years.

Television

Malcolm J. Norwood

As television grew in popularity, there were some attempts at optical subtitles in the early years, but these were not wildly successful nor widely adopted. In the United States, there was interest brewing in closed captioning systems by the end of the 1960s. In April 1970, the FCC received a petition asking that emergency alerts be accompanied by text for deaf viewers. This request came at a perfect point in time when the technology was ready, and the various parties were interested and prepared to take on the challenge.

It was at this time that deaf bureaucrat Malcolm Norwood from the Department of Education (then HEW) enters the story. He had been working in the Captioned Films for the Deaf department since 1960. Today he is often called the Father of Closed Captioning within the community. He was the perfect leader to champion this new technology and he accepted the challenge.

The FCC agreed in principle with the issues raised, and in response issued Public Notice 70-1328 in December 1970. Malcolm and the DOE brought together a team in 1971 which included the National Bureau of Standards, the National Association of Broadcasters, ABC, and PBS. They held a conference in Nashville (PDF) in December of 1971, which we can say was the birthplace of closed captioning.

First Captioned TV Program in 1972, The French Chef hosted by Julia Child. These were Open Captions and could not be turned of by the viewer.

It turns out that the technical implementation of broadcasting captions built on existing work. Over at the the National Bureau of Standards, engineer Dave Howe had been developing a system called TvTime to distribute accurate time signals over the air. This system sent a code over a video line in the VBI, using a method which eventually morphed into the CC standard. They had been testing the system with ABC, PBS, and NBC. ABC had even begun using this system to send text messages between affiliate stations.

Another system presented at the conference by HRB-Singer altered the vertical scanning of the receiver so that additional VBI lines were visible, and transmitted the caption text digitally, but visually, in those newly-exposed lines. This caused some concern among the TV set manufacturers, and thankfully the NBS system eventually won out.

After a few promising demonstrations, in 1973 PBS station WETA in the District of Columbia was authorized to broadcast closed captioned signals in order to further develop and refine the system. These efforts were successful, and in 1976 the FCC formally reserved line 21 for closed captions.

Adapting Broadcasts for Line 21

This is an index card that kicked around in my briefcase for many years. Can you spot the error?

In its final form, the signal on line 21 had a few cycles of clock run-in to lock the decoder's data recovery oscillator, followed by a 3-bit start pattern, and finally two parity-protected characters of text. The text encoding is almost always ASCII, with a few exceptions and special symbols considered necessary for the task. Text was always transmitted as pair of characters, and has traditionally been sent in all capital letters. Control codes are also byte pairs, and they perform functions like positioning the cursor, switching captioning services, changing colors, etc. Because control codes were so crucial to the proper display of text, parity protection wasn't enough -- they were usually transmitted twice, the duplicate control code pair being ignored if the first pair was error-free.

| Summary of Line 21 data
---|---
Basic Rate | 503.496 kBd (32 x Horiz freq)
Grouping | 2 each 7-bit + parity bit characters / video line
Encoding | ASCII, with some modifications
Services | odd fields: CC1/CC2, T1/T2
| even fields: CC3/CC4, T3,T4, XDS
Specification | EIA-608, 47 CFR 15.119, TeleCaption II

Today we are accustomed to near-perfect video and audio programming, thanks to digital transmissions and wired/optical networks. Adding a few extra bytes into an existing protocol packet would barely give us pause. But back then, other factors had to be considered. The resulting CC standard was fine-tuned during lengthy and laborious field tests. The captioned video signal had to be robust when transmitted over the air. Engineers had to address and solve problems like signal strength degradation in fringe reception areas and multipath in dense urban areas.

Pop-On CC Demo Frame from Felix the Cat

As for the captioning methods, there were a few different types available. By far the most common styles were POP-ON and ROLL-UP. In POP-ON captioning, the receiver accumulated the incoming text in a buffer until receipt of a "flip-memory" control code, whereupon the entire caption would immediately appear on-screen simultaneously with the spoken dialogue. This style was typically used with prerecorded, scripted material such as movies and dramas. On the other hand, with ROLL-ON captioning, as its name implies, the text physically rolled-up from the bottom of the screen line-by-line. It was used for live broadcasts such as news programs and sporting events. The text naturally must be delayed from the audio due to the nature of the live speech transcription process.

The Brits Did it Differently, and Implemented Teletext in the Process

Across the pond, broadcast engineers at the BBC approached the issue from a different angle. Their managers asked if there was any way to use the transmitters to send data, since they were otherwise idle for one quarter of each day. Therefore they worked on maximizing the amount of data which could be transmitted.

The initial service worked like a FAX machine by scanning, transmitting, and printing a newspaper page. Eventually, the BBC adopted an all-digital approach called CEEFAX developed by engineer John Adams of Philips. Simultaneously, a competing and incompatible service called ORACLE was begun by other broadcasters. In 1974, everyone finally settled on a merged standard called World System Teletext (WST) adopted as CCIR 653. Broadcasters in North America adopted a slight variant of WST called the North American Broadcast Teletext Specification (NABTS). Being a higher data rate than CC, teletext is less forgiving of transmission errors. It employs a couple of different Hamming codes to protect and optionally recover from errors in key data fields. It is quite a complex format to decode compared to line 21.

British Radio Equipment Manufacturer’s Association, Broadcast Teletext Specification

As for the format, teletext services broadcast three-digit pages of text and block graphical data -- conceptually an electronic magazine. Categories of content were grouped by pages:

Example of Teletext Magazine Page

• 100s – News
• 200s – Business News
• 300s – Sport
• 400s – Weather and Travel
• 500s – Entertainment
• 600s – TV and Radio Listings

These text in these magazine pages are an integral part of the packet structure. For example, the text of line 4 in page 203 belongs in a specific packet for that page/line. Since the broadcaster is continuously transmitting all magazines and their pages, it may take a few seconds for the page you request to appear on-screen. NABTS takes a more free-form approach. The data can almost be considered a serial stream of text, like a connection of a terminal to a computer. If you need a new line of text, you send a CR/LF pair.

| Summary of Teletext Data
---|---
Basic Rate | 6.938 MBd
Grouping | 360 bits/line, 40 available text characters
Encoding | Similar to Extended ASCII, with code pages
Services | Multiple page magazines, 40×24 chars each page
Specifications | Europe: WST ITU-R BT.653 (formerly CCIR 653)
| North America: NABTS EIA-516

The Hacks That Made It All Work

Most of my designs were for use in North America, but I needed to learn about European teletext for a few candidate projects. In Europe, page 888 of the teletext system was designated to carry closed captioning text. This page has a transparent background and the receiver overlays it onto the video. The visual result was practically the same as in North America. But it posed some problems regarding media like VHS tapes.

The teletext signal couldn't be recorded or played back on your typical home VHS recorder. To solve this, many tapes were made using an adaptation of the North American line 21 system, but applied to the PAL video format. This method was variously called line 22 or line 25 (the confusion being that PAL line #1 is different place than NTSC line #1), but was basically the same. A manufacturer who has a CC decoder in their NTSC product can easily adapt it to work in PAL countries.

How did I get PAL VHS tapes? I asked an engineer colleague at Philips Southampton if he could send me some sample tapes for testing. His wife bought some used from a local rental store and sent them to me. This was before the days of PayPal, so I sent her an international money order for $60. This covered the price of the tapes and shipping, plus a few extra dollars "tip" for her trouble. Some weeks later, I got an email from him saying that "you Americans sure give generous tips". His wife had received my money order for $600, not $60! It took many months, but eventually the post office caught their mistake and she returned the overage.

The Author Troubleshooting a DVD Closed Caption problem at LG in 2003

In South Korea, a colleague was involved in the captioning industry back in the late 1990s. He was asked to participate on a government panel considering the nationwide adoption of closed captioning. The final result was comical -- instead of CC, the committee decided to provided extremely loud external TV speakers free-of-charge to people with hearing difficulties. Fortunately, the conventional form of closed captioning has since been adopted with the advent of digital television broadcasting.

Designing on the Trailing Edge

By the year 2000, almost all televisions had CC decoders built-in. As a result, there were a variety of ICs available to extract and process the line 21 signal. One example was from Philips Semiconductor (which became NXP and is now Freescale). As a key developer of teletext technology and a major chip supplier to the television industry, they offered a wide variety of CC and teletext processors. I developed several designs based on a chip from their Painter family of TV controllers. These were 8051-based microcontrollers with all the extras needed for teletext, closed captions, and user menus. They had VBI data slicers, character generators and ROM fonts, all integrated onto one die.

Philips Saa55xx datasheet (page 91)

I still remember discovering the Painter chip buried pages deep in an internet search one day. When I couldn't find any detailed information, I called the local rep and was told, "You aren't supposed to even know about this part number -- it's a secret!". Eventually the business logistics were resolved and I was allowed to use the chip. That was the only masked-ROM chip I ever made. I can still feel the rumbling in my stomach on the day I delivered the hex file to the local Philips office. The rep and I were hunched over the computer as we double- and triple-checked each entry on their internal ordering system. Once we pressed SEND, the bits were irrevocably transmitted to the factory and permanently burned into many thousands of chips. Even though we had thoroughly tested and proven the firmware in the lab, it was nevertheless a stressful day.

Philips Painter Chip

As I developed several other designs, it became clear that these special purpose chips should be avoided if any reasonable longevity was needed. The Painter chips were being phased out, several other options were disappearing as well. The writing was on the wall -- digital broadcasting was here to stay, and the chip manufacturers were no longer making or supporting analog CC chips. I decided that future CC projects had to be done using general purpose ICs. I plan to delve into that in a future article along with unexpected applications of CC technology, the process of making captions, and how captioning made (or didn't make) the transition to digital broadcasting and media.

#hackadaycolumns #history #originalart #analogvideo #closedcaptioning #line21 #nabts #ntsc #pal #subtitles #teletext #vbi #wst