Call of Duty: Black Ops 4 famously broke series tradition by ditching its campaign to focus entirely on multiplayer, with Treyarch instead opting to tell its lore through a comic series, of all things. Most players resigned themselves to never seeing what had been planned - until now, perhaps, as footage of the cancelled campaign gameplay appears to have popped up online.
As posted on Reddit, the gameplay shows some limited footage of a campaign mission in which the player must shoot terrorists (while avoiding citizens) and find the Aquilus CEO, whoever that may be. The person who posted the leak, a Reddit poster by the name of ForeverDexus, claims to have found the footage online in an "incredibly obscure" place, along with further footage of the Black Ops 4 engine in pre-alpha and another video of the cancelled campaign.
At first glance, it looks pretty similar to Black Ops 4's multiplayer: the HUD looks nearly the same, while the level takes place on multiplayer map Seaside. As the NPCs look rather... blue, it's fair to say the footage comes from a fairly early build of the level.
The similarities to Black Ops 4's multiplayer could be explained by the fact the campaign was supposed to be a unique 2v2 multiplayer experience. According to Kotaku's sources, players would pick a faction and battle against each other to complete opposing objectives: a project which eventually reached the demo stages before the studio reportedly tried to morph it into a traditional single-player story. By early 2018, Eurogamer heard the campaign had been scrapped entirely to focus on developing the multiplayer. Treyarch co-studio head Dan Bunting also told Eurogamer that there was "never a traditional campaign" planned for Black Ops 4, which may also explain why the gameplay looks far closer to multiplayer than the more on-the-rails campaigns seen in other Call of Duty titles, such as the recent Modern Warfare.
It's probably not the best indication of what Treyarch's campaign would have looked like - which sounds like it changed several times, anyway - but the footage is an interesting peek at what could have been.