Thomas Worth swears he didn't expect any of this. He never expected that, 10 days after it launched, VHS Camcorder, his goofy $3.99 video app, would be No. 2 on Apple's chart for paid apps, second only to Minecraft. Or the torrent of email, tweets, and castigating for an Android version. (It's coming, by the way.) Most of all, he didn't expect people to love this crappy retro look as much as he does.

No, when he decided to create an app that makes your video look like you shot it 1985, it seemed like a fun thing to do. "I expected people to like it," he says, "but I didn’t expect this many people to like it." His grandest ambition was a shoutout from celebrity videographer Philip Bloom. "Whatever," he says. "It would be fun for a month or two."

Worth is 38, a child of the '80s, and an unrepentant lover of that decade's wacky graphics and messy technology. He's been doing post-production and effects in LA for years, and in his free time occasionally would screw around in After Effects and upload ultra-'80s takes on the logo of his company Rarevision. One, featuring laser-lit stencils flying in to the sound of an epic synth track, struck a particular chord. "I put it on YouTube just for the hell of it," he says. "People were like, 'Oh my god, that's so cool, can you show me how to do that?'" He realized there was something nostalgic but also flat-out appealing about the decades-old aesthetic. He wondered, Could you make an app that would make your video look like an old tape?

"Doing it in After Effects is one thing," he says. He could do that in a few hours. But writing an app that let anyone do it was a much bigger undertaking. "I figured I’d have to really put the time into this and make it realistic." In its final form, VHS Camcorder is a full-fledged camera app; it can shoot video in three resolutions, in color or black and white, and in widescreen or old-school 4:3. Still, let's be clear: "full-fledged" is sort of a misnomer. VHS Camcorder shoots terrible video. But it's a very specific kind of terrible.

The amateur videos from that era have a lot in common. They have those wiggling tracking lines, usually across a third or so of the screen. They had a particular color gamut, maybe some ghosting from old videos you'd recorded over, and the ultra-familiar timestamp in the bottom left corner. There's a science to this stuff, all of it baked into how VHS Camcorder processes video as you shoot it. "I basically had to learn how to be a video tapedeck repair man to figure this out," he says. He learned about helical scanning, the process used to record video and audio onto tape. He learned about deck architecture, how one VCR plays records ever so slightly differently from the next. "What can go wrong in that situation to produce these artifacts?" he asked himself.

Then he started watching YouTube videos. A lot of YouTube videos. "Oh my god, man," he says. "For like, months, I was on Youtube just searching every awful, crappy video that people had digitized and put on YouTube. Every crappy digitized video I could find." One compilation, an hour-long compilation of '80s commercials, was particularly instructive. Over time, he—a visual effects and post-production wizard with a well-trained eye for this stuff—started to see patterns. Certain kinds of distortions, themes with the tracking lines he'd notice over and over. Then he'd sit down at the Mac app he'd thrown together to test his ideas and tweak his settings. Over and over, trial and error, trying to get the feeling exactly right.

VHS Camcorder

The app's interface is based on the JVC GR-C1, the first camcorder to feature a built-in VHS tape deck. Released in March, 1984, the GR-C1 is probably most famous for being Marty McFly's camera in Back to the Future. (It's also the reason you can't set the time in VHS Camcorder earlier than March, 1984; it's not historically accurate, Worth says.) The app's blue Menu button matches the GR-C1's styling, as do the huge W and T buttons for zooming in and out. Worth designed an entirely new character set for the timestamp, which is an amalgam of every camcorder font he could find. The typeface, he says, was crucial: it's a huge part of the videos everyone remembers. Get it right, and you're already halfway there.

There are a few features in VHS Camcorder that Worth added just for fun, like the aptly named "Tilting Devices Makes Things Worse" setting, but virtually everything else is made as true-to-life as possible. Adding zoom came late to the process, largely because it runs completely counter to everything Worth believes as a filmmaker. "One mandate throughout my education on this," he says, "has been don’t ever zoom during the shot. Just don’t ever do it. And people who shoot with camcorders don’t know that." Late in the app's development, a tester suggested adding the feature, and Worth jumped on board. He knew exactly how to do it, too. "I think it’s just that really annoying, slow, like trying to be clever slow zoom feature," he says, "where you’re trying to have people not notice but it’s totally obvious."

Eventually, he had it. The tracking lines flickered just right, the camera shook, moved, and distorted perfectly. Well, maybe not perfectly, but close enough. "I got really excited," he says. "I was like, 'Oh my god this is going to look amazing.'" Then he put it on his iPhone, ready to test the app. "And it runs at like 2 frames per second." Turned out, it was next to impossible to do this kind of real-time conversion and rendering on a phone.

Now, he says, VHS Camcorder is built like a video game. "The entire rendering is done on the GPU," he says. "That’s the only way it’ll work." He's mad he couldn't get it working on the iPhone 4 he has on his desk, and is still sort of shocked it worked on the 4S. "There’s like a million rendering passes on this thing, and each one puts another layer on the video." The game comparison goes deeper, too. This isn't a filter, Worth says. It's not like slapping Mayfair on top of your Instagram photos. "The idea is, this thing is a simulator." He doesn't care if you think it's not how a VHS looks; it's exactly how a VHS looks. He has the VHS tapes, the decks, and the videos to prove it. "You're going to have to change your opinions in order to appreciate it," he says, "because your perception is wrong."

Luckily for Worth, most people already seem to get it. He's working on adding features, like front-camera and flash support. In the last few days, VHS Camcorder has received huge press, and the $3.99 app is clearly raking in money—Worth declines to say how much, but "I'm really happy with the sales." Its most prominent moment came when Wiz Khalifa was violently arrested on a "hoverboard" in LAX, and shared a video shot in VHS Camcorder. At that point, Worth says, "the app had only been out for like two days I think, and not everybody knew about it."

There were comments all over Khalifa's tweets and Instagram posts, many of them wondering the same thing: Why does this video look like it was shot 30 years ago? That was music to Worth's ears. "That made me feel good," he says. "People were fighting over whether it was an app!"