One of the final nails was the infamous Chrome 45 aka the Chromepocalypse in the video ad world.
Chrome 45, in the name of performance, defaulted to only loading flash from 3rd party domains after a "click to load". This was bad for ads for obvious reasons, but it was much much worse due to an implementation detail.
In order to get the page laid out properly, Chrome loaded the flash component and then suspended it after a single frame. From an ad perspective, that was enough to trigger the impression pixel, signifying that the ad had been shown and the advertiser should be billed. However, the ad was not shown and there was no way for the ad to detect it had been suspended. Just a nightmare. We (I led the effort at BrightRoll) had to shift a ton of ad auction behavior to special case Chrome 45 and it limited what kind of ads we could serve.
That was the inflection point away from flash for ads. While ad formats like VPAID supported JS/HTML5, they didn't start getting popular until after Chrome 45 was released.
I've been out of the space for about a decade, so I can't say how things have continued to evolve, but the only consistent antidote to fraud has been a trusted third party.
I spent a lot of my time back then pulling in metrics from third parties like Nielsen (who do traditional TV viewership numbers) as well as companies who specialized in "viewability". We could include that data in our real-time auction and bidders would adjust what they were willing to pay based on the reputation of the ad opportunity. At least that's the theory. In practice there was so much indirection and reselling that it was hard to say what was true.
As far as the technical answer: it's a game of cat-and-mouse but we found some interesting metrics we could dig in on. One was that fps of a video hidden behind another element on the page would have a drastically different rendered fps than one in the foreground. That would be different between browsers (and browser versions) but the viewability vendors would find all those quirks, measure, and analyze to give us a normalized score. For a hefty fee, of course.
Percent In View = Area of the Intersection of the Ad and the Viewport / Area of the Ad
You would get the area of the ad using getBoundingClientRect, and the area of the viewport using window.innerWidth and window.innerHeight.
It was not possible to do this if the ad was within a hostile iframe (cross origin iframe) so you needed to use a third party source for this information like SafeFrame.
All of this was greatly simplified when Intersection Observer was officially supported by modern browsers.
> I imagine it has to be somewhat "bulletproof" since money is involved.
The GP comment pretty much shows how bulletproof it wasn't, it isn't, it never will be. You also have bad actors in the space that will load ads under other ads so that the same page load continues to generate impressions. The space behaves as if there is no incentive to be honest.
Flash game sites were still huge and popular after Adobe’s purchase, so clearly it did not kill it. If you mean something like that the acquisition started the death… that’s a hard position to argue against, since it’s subjective. Perhaps you’re right.
When flash started to fade for games, many developers moved over to adtech where their skills were still valued. Flash continued for a few years to power ads as well as shims around other videos that would collect data and even trigger secondary ad auctions.
Adobe had competing products mostly based on open standards. They shut down many active product lines and merged what was left into Adobe AIR, which didn't take off.
Chrome 45, in the name of performance, defaulted to only loading flash from 3rd party domains after a "click to load". This was bad for ads for obvious reasons, but it was much much worse due to an implementation detail.
In order to get the page laid out properly, Chrome loaded the flash component and then suspended it after a single frame. From an ad perspective, that was enough to trigger the impression pixel, signifying that the ad had been shown and the advertiser should be billed. However, the ad was not shown and there was no way for the ad to detect it had been suspended. Just a nightmare. We (I led the effort at BrightRoll) had to shift a ton of ad auction behavior to special case Chrome 45 and it limited what kind of ads we could serve.
That was the inflection point away from flash for ads. While ad formats like VPAID supported JS/HTML5, they didn't start getting popular until after Chrome 45 was released.