What is 525-Line Analog Video? 

Again, the reason he can use words like ‘about’ and ‘approximately’ is because it was all analog. Unlike digital, there were no discrete, perfectly defined packets of data in analog..

CRT TV’s were some of the most awesome machines ever invented.

This channel deserves more attention than it's getting.

Back in the day, they didn't tell us, it's 576 lines or 486 lines, respectively. I was told, we've got 625 lines and across the Atlantic, they've got 525. I then computed out that with 4:3 ratio a line would have 833⅓ pixels. I had a close look at the screen, the screen was a cromaclear shadowmask, and I saw the hexagonal structure. I concluded that some lines have more pixels than others, some have 834 lines, other 833, on average 833⅓. How wrong I was. The literature I had back then didn't make things clear. Nowadays, young people have never heard about the numbers 625 and 525. They only know SD as 480 in NTSC and 576 in PAL.

Oh i get it now. CRTs are magic.

This is really interesting because I remember we had a really old CRT TV with v-sync and h-sync knobs that would distort the image (and I used to play with them). Now it makes total sense why the image was distorted that way. I really loved this video ! Thanks a lot for the great explanation!

The one detail that really helped this all click home to me when it was pointed out, is that the vertical scan is constant - the electron beam is always moving down, even as it scans across each scanline. This means that the scanlines are very slightly diagonal, as the beam moves down by most of a line as it goes from left to right across the screen. This is how the half-line offset makes the interlacing work - by starting one field at the top left of the screen, and starting the second field at the top middle of the screen, the scanlines for each field gets nestled between the scanlines for the other field. This is why the total number of lines, 525, is odd.

I just discovered your channel earlier this week. It's become one of my favorites. Keep it up man!

The VBI pulses may seem repetitive, but they are pretty important if you want a picture on your screen. Remember that television was developed using vacuum tubes and 1930s discrete components and that ancient stuff had to not only sync up with a broadcast signal, but contend with poor signals as well. A lot of NTSC's design choices come from the limits of technology at the time.

I love these videos man, great work as always. I don't know what it is in our nerd brains that makes this stuff so interesting, but I love it.

The reason for the half-lines in interlacing is interesting. Horizontal scanlines aren't really exactly horizontal. They slope down slightly from left to right. The is because the vertical downward deflection of the beam continues as each line is drawn. To get interlacing a vsync happens halfway during a scanline so that the next field's lines end up starting at the level of the midpoint of the previous field's slightly sloped lines.

The style of these videos makes it so much easier to understand

One interested tidbit is that analog TVs didn't have pixels. The electron beam just varied in intensity as it moved left to right. So there was no definitive horizontal resolution for an analog signal. If anyone wants to learn more, the channel Technology Connections made some good videos on analog TV, and Texas Instruments has an application note about CRT displays entitled "Understanding the Operation of a CRT Monitor." With the application note number AN-656. It's a good place to start digging deeper, for those interested.

Displaced Gamers - JAPAN had MUSE High Difinition ANALOG TV in 1985, they had 1 channel Dedicated to MUSE Broadcasts and it was even LIVE Broadcast from the Japan Worlds Fair in 1985. the Worlds Fair also featured the Analog High Difinition TV camera and the High Difination TRINITRON Display.

This is the best explanation on how CRT/tube TVs work in displaying the picture based on data.

625/576 line analog video in europe was great as we had wonderful teletext, that i could check news, betting, etc. on the TV!

Great visual and technical explanation! Especially on the half lines and how it makes the video interlaced (or not).

The algorithm suggested your channel and after several videos of well thought out content, and clearly made with love, have not been disappointed. Subscribed and eagerly awaiting more!

Great job! I loved it! I deal with so much AVC and MPEG2, that this review of CRT tech is a refresher.

I just found your channel last month right around the time i started working with video signal, and then you start making videos on em, great videos.

That was incredible! Way more thought and attention went into CRT TVs than I ever realized, but it certainly explains how heavy they were: a lot of stuff going on in there!

Great Video, never seen the inner workings of the blanking intervals. I learned several things from this video. Keep it up!

That 80s VHS demonstration is such an eye opener.

1:02 gotta admit I was expecting it to hit the top left corner.

I would appreciate it if you added Closed Caption. And thanks to you, I've learned how overscan works.

I finally found a channel to give me the answers. Not noly FPS and delays, but explanation. Love it

My recollection is that the notion of 480i was born with the notion of digital TV and DVDs. Before that I don't recall anyone ever saying "480i", it was just NTSC.

You should advertise your channel. This type of great content must dominate RU-vid.

Fantastic video, thank you so much!

Good job and thank for sharing. It's valuable info after all

Grew up with CRTs, used emulators in the mid 90's-and 2000's. Back to the original hardware and a PVM these days. It's really the best way to do it. And as mentioned in other videos, even component has its merits, so I'm looking forward to getting a nice Trinitron when I have the space.

Very interesting video. Keep up the good work!

Found your channel today and already watched about 6 videos of yours. Great content! Subscribed!

excelent work. solid information. subscribed. +1 for the keen 4 music

When you already know your stuff but you still watch the video because it's enterteining as heck.

J.R. Ewing what a blast from the past. Lol Great video man.

Love the video!!!

I've always wondered how CRT TV's functioned. Had no idea "480p" has been around since the 40's, that's amazing!

Really cool and well done

Followed the link from RetroRGB. This was great info.

Bets video on the subject. Subscribed!

Your videos are my cup of tea. Nerdgasms abound!

I'm subscribed !!! Fantastic Video. I love Crt Technology. Today i have a mini collection of Crt projectors !!!!! Thanks for the video !

I'm watching through your videos, having just discovered your channel. Fascinating stuff. Even though I worked with home computers since the early 80s, there are some things I still didn't know about luma, chroma and NTSC. One thing you didn't cover, however, is how live analog TV, and its recording on videotape, carries 60 intervals of motion per second even though there are only 30 full frames per second. Each field is a snapshot in time, and doesn't have to match either of the adjacent fields in the timeline. So the result looks like 60 fps even at full 480i res. Given the strobing effect of CRTs, that motion looks perfectly smooth too (unlike the sample-and-hold tech of LCDs).

This is just awesome!

You get a like an sub just for the Dallas footage.

Loved how you showed off Warlords for your Atari display. My favorite Atari game. It's worth noting how little time Atari games had for logic. Any and all game logic/input/sound/etc had to fit in between the horizontal and vertical blank periods. All the games had to perform the display rendering themselves in software. Part of the reason the games were so simple - you had to spend like 90% of your compute cycle just rendering the image in real-time. NES (and maybe some others prior to the NES, unsure), had dedicated graphics chips that rendered in parallel to the game doing logic for the next frame.

Significantly more complex than I expected!

Very nice video to listen to. I love listening to information content while gaming for backgrounds noise and entertainment, and i found a new channel for that

Awesome video. I'd love to see more info about how game consoles use the blanking intervals or overscan to let the cpu run operations.

Great video. You are a bit like Technologie Connections but a bit lighter in the intensity when it comes to technical informations.

there's just something so interesting about learning why the most mundane things work... like, who ever thinks "huh, i wonder how this 30 year old TV works?", yet here i am, spending 15 minutes of my life learning about it

Man, this is great stuff!, really interesting to see how it all works. Now I know what those dark lines with a square half way through that quickly move up are when I fist turn on my rf or composite devices, I guess the television I guess the television doesn't get all the lines right away and accidentally draws them?

This extra res is also a thing in current digital signals. Also google "Scanline sync". That's the best vsync alternative we have cause it eliminates vsync input lag.

Think of the electron beam as a pen, which has momentum when it moves. When the line ends, it still has the momentum from moving to the right for so long, so it literally has to slow down, go to the left for awhile to return to the beginning, turn around again, and start moving right for the next line. The H-sync interval accomidates this. Also, it was never just 525 and 625, there was a bunch of bespoke TV systems which all worked more or less the same way, but with different settings. The BBC used 405 lines for awhile, and the 525 line system was *originally* a 441 line system that then got upgraded. The first BBC TV broadcasts were 30 lines, mechanically scanned. It later got tweaked into a 32 line system that oldschool hams sometimes used over shortwave. Incidentally, the mechanical systems theoretically didn't need an H-sync pulse, as the mechanical scanners were able to start new lines instantaneously due to their geometry.

Really old TVs some times had flop over with closed captioning signals- leading to white lines and dots at the top of the screen. The TV guy was able to fiddle with stuff in the back of the set to fix it.

7:52 - I always wondered why there was half a line missing at the bottom of the picture when a local TV station was still using analog cameras on a digital transmission, that clears it up, thank you! 11:23 - I wish there was an easy, reliable way to capture closed captions from analog video, seems to be a feature either missing or an afterthought on most capture cards :s

I love that Neon graphic / visual nod to 80's and 90's. ☘️👍

When you bought 'pay-per-view porn' in the 80's you were buying horizontal sync pulse.

I kind of wish you had covered Teletext as well. One of the most fascinating uses of the spaces left by vertical blanking!

Very good explanation of analog video. The Atari 2600 works quite a bit differently than other videogame consoles. It can display more (or less) than 192 lines, that is just the number Atari recommends in their documentation. The programmer has almost total control over the video signal timing and it is their responsibility to set when the HBLANK and VBLANK and VSYNC signals are produced by the TIA chip. By reducing the VBLANK period, a taller game display is possible. I've achieved a stable display as tall as 230 lines, though what is possible and how much is visible outside the overscan area is largely dependent on the television. That's why a conservative 192 scanlines is recommended.

Invented in the U.K., then used in most of Europe, we had the teletext service transmitted over the air in the ‘spare line’, a service that offered hundreds of selectable pages of information without the need for a modem or computer. For some reason the US, did not make much use of the system and I believe only one cable network actually used it.

Well explained.

the green vertical line within the horizontal sync pulse was the color burst signal.

So that's how it works! Wow thanks for sharing! Right on dude! B)

Sometimes a defect in the video amp could cause the otherwise blanked retrace lines to become visible. Or could be caused by what was known as "poor grid cutoff" characteristics in the cathode Ray tube.

Funny that you mentioned KHOU Channel 11 from Houston. Right before they aired Dallas, we'd watch the Dukes of Hazzard on Friday nights on the same channel.

Most 8 bit computers had processors that could run in parallel with the video hardware dumping screen data to the CRT.

Front door back porch vertical blanking horizontal blanking 2 fields a frame....wow I'm glad I still engineer for the media. Such a history of technology......no sync pulse acts like a blurry picture.

The aspect that isn't really explained here is how a half scanline can cause a shift in the field position: It's because the horizontal lines aren't actually perfectly straight, but due to the horizontal waveform, slightly bend to the next field position.

Great video. You forgot to mention the chroma burst located in the horizontal blanking interval.

For an expanded lecture(?) on CRT TV, check out Technology Connections extensive series on the history of television.

If you got two stations on the same channel, you could see the VBI, and even some picture. Stations were offset by 10KHz, so you’d get a beat in the audio and video. I got a few faraway station IDs that way. Some VHS recordings on RU-vid have it.

Interesting trivia, because of the way the Atari 2600 controlled the video output (with the game itself control the HSYNC and VSYNC to an extent) it's possible to create an interlaced image. It has been done with real hardware as a proof of concept around 2001, but I'm not sure if any games actually use it.

On the second pass (odd lines) the tv is drawing the video fields of the next frame, not the current frame. Interlaced video is sacrificing vertical resolution for temporal resolution.

small note, if you send 2 different fields per frame you can achieve 60fps using 480i instead of the usual 30fps that the format was designed for.

Actually, the vertical hold process typically starts at the bottom (visible if you can see the bottom of the raster), then the rest of the bar is drawn on it's way up, including the other half of the sync process. On an older TV (70s, back), you can see this with adjusting brightness, and contrast, as well as the retrace lines with vertical hold slightly off-sync. You can also view the copyright protection on DVDs/Tapes as well, as the beam always is drawing (it uses the black portions as "Blanking" the physical image, as that technology didn't exist then). It draws a pair of 4 black, and super-black boxes in the vertical bar retrace region. When this happens, you can see the white parts fade in, and out of the image on the upper-left of the display, because the older TVs didn't blank the raster at any point.

13:10 cool, I always was wondering about those colorful dots on the bottom on the Sega display :D in PAL region we see them :P another fuck PAL situation :D haha

"Now is a good time to pause the video and make a sandwich." Well, I think I will! *pause*

Gotta love that Seaquest on the Atari! []

This is where the copy protection company "Macrovision" got its name. The protection occurs within the horizonal "blanking bar" between the frames by intermittently adding white blocks that only allow the video signal to go to your TV. If you attempt to record that bar, the resulting intermittent blocks cause the contrast (luma) to fall below standard interfering with it.

I had a general idea of how this worked, but never knew the magic number(s). I do recall using the 640x400 interlaced mode on my Amiga and getting a headache.

most 240p consoles seem to use 524 lines... but I've noticed that my n64 puts out 526, interesting stuff

I did paused the video and made a sandwich. Awesome content! 🔥

Late to the party, but I had to observe: So, the reason that we have these scanline filters for our retro games is that they were always only drawing to field one? Because they were doing the '240p' signal, the horizontal lines were only ever drawing the odd lines (sorta), skipping the even lines (again, sorta. I understand we're using digital terms to try to describe analog processes) by setting up another field one frame? And those blank even lines gave us the lined images that we remember so fondly? Mind blown.

This was fun to watch... Now for the headache, it's analog, there is no autoadjust of the electron beam, it was fixed timing setup at manufacturing by setters with a screwdriver and in fact you can also say the beam always runs the full lines, just it does a blank travel in interleaved mode and could perfectly run non interleaved (though it would cause some glitches and flickering visible and that's why TV were interleaved) With time and wear, the pulse could unsync, barely visible if not a slightly blurry or deformed image because the beam is a bit too high, too low on the tv grid or the speed of it isn't right. This is then you know your tv tech is a master or just crappy one! And add more... broadcast standard, NTSC, PAL or SECAM

I always wondered what the heck was going on when I had to play with the Vsync button on the VCR to get the image to stop blink shifting up

I love these older "technology" videos a lot, including the Luma and Chroma videos, but they sadly seem to have mostly died with that Chroma video. I get why; the view count on the "game code" videos seem higher, so it makes sense to focus on those. Not that they're bad, I just wish we could have more of a mixed bag.

Nobody talks about how different stations are not all broadcasting in sync with each other. This is why a TV needs to be able to suddenly change its timing; why each line and each field has its own tracking information. Imagine if the signal didn't include that data, and the TV was just timed to display everything on an internal timer; it knows to move to draw the new line exactly after a certain time, and draw a new field exactly when all the lines are drawn. Now imagine you change the channel. There is no way that the new station would be broadcasting at the same rate down to the microsecond so that each new line is broadcast as exactly the same time. Your TV could be drawing the image in the middle of the screen but the new station happens to be drawing a new field. Even if the stations were timed to each other, the fact that your antenna would be a different distance from the broadcast source would naturally result in the radio waves being out of sequence anyway. This would naturally force the viewer to manually adjust the settings on their TV for each channel to properly position the image in the middle of the screen. Quite a hassle, so instead the syncing information was designed to occur in the signal itself. This is why, when you changed channels, the image would "flip" for just a fraction of a moment. The image wouldn't line up right for just one frame because the two channels were not in sync with each other. Nobody mentions this, and it is not really possible to demonstrate anymore, but this happened back in the day. Also, do you recall seeing poor staticy images that would scroll up for a moment or two? (This effect certainly has been shown in various shows and movies before.) Remember, these signals are all analog, so if the signal to start a new frame came in too weak for a TV to identify that's what it was, then the image would not be able to correctly determine where the new frame starts. These pulses that are used to sync the images are not functionally different from a proper signal, they are just effectively lower (or darker/blacker) than the rest of the image. And being all analog, some TV's might be more (or less) sensitive to this new-line command than others. Fun fact: There is a certain range of blacks in the NES's color palette that were so dark that they could trigger some TV's to start a new field. No officially licensed NES game was allowed to use those colors because they could cause the image to lose its vertical hold.

Amazing work! Really amazing! How long does it take to make a video like this? Btw I was actually considering pausing this to make a sandwich, and then you said it. No joke. :)

The Amiga computer is the only computer really designed to control, and display correctly on, a CRT TV. Even so the 625 line PAL standard can only have 576p maximum output to the TV/monitor.

how could be so complicated the way of the analog TV works back to an era were the electronics were far less developed than now?

So to explain it simply, not all 525 lines are used for the picture.

I understood at least half of this

0:25 You're kind of wrong about that. Interlace only shows half the fields at a time. The switch is so quick you only see a complete image, but there's really only half an image being displayed at a time. It's not like it completes both fields to produce a full image. In interlace displays, there is NEVER a full image on screen.

I came for the J.R. Ewing thumbnail

Television magic, got it.

I have a question, I understand that sync signals help stabilize the image, but what's the actual physical process of "locking" to the sync? I was always confused about this. Does the electron beam never stop moving? or does it finish the lines before the sync signals stops and "waits" for the sync signal before proceeding? If it never stops moving, how does the beam adjust when it receives the sync signals?

Great video, but who IS the model pictured??

*And love my Super Nintendo sir!* ❤️ ❤️ ❤️