How Unreal Engine and Houdini power the VFX of Surviving Earth
by https://www.creativebloq.com/author/james-clarke · Creative Bloq
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Ask most people what visual effects artists do and you’ll usually get the obvious answers – wild creatures, huge explosions, vast impossible landscapes stitched together in post, maybe just name-check this year's big Marvel movie – but speak to Enrico Selmi, co-head of VFX at Milk VFX in London, who worked on new nature documentary Surviving Earth, that explores eight mass extinction events stretching back 450 million years, as it follows the lives of the creatures that came before the dinosaurs or lived alongside them, and the focus moves almost immediately away from imagery and into something far less visible: data structures, workflows, pipelines, and USD, which doesn’t sound especially cinematic until you realise it underpins almost everything that ends up on screen.
Selmi’s role, as he describes it, sits right in that space between creative ambition and production reality, “Ultimately, my role is about helping the team deliver great VFX that match the client’s vision while keeping the project moving smoothly,” he says, adding that a large part of the job is simply keeping those two forces aligned, “balancing the creative ambition with what’s technically achievable for the show.”
That responsibility runs through the entire life of a project. “I follow project execution and design from when they enter the door all the way until they are archived,” he explains, and that means everything from structuring teams and shaping workflows through to very practical questions about how the pipeline actually holds together in production: “Is it going to be efficiently running? Is it going to fit the server? How are we distributing the data?”
It doesn’t end once the work is underway, as Selmi explains: “I also attend to design workflows and data management, meaning: how do we store the data? How do we delete data when the project is live and when the project is completed, and how is it archived?”
The impact of USD
A shift in how that data is handled led Milk VFX to adopt USD (Universal Scene Description) more seriously around two years ago, implemented through Houdini and increasingly embedded into the studio’s pipeline. USD, developed at Pixar and released as open source in 2016, is often compared to Alembic (used to 'distil' complex, animated 3D scenes into baked scenes) or FBX (a file format used to move 3D assets between apps), though Selmi first describes it in simpler terms: “It’s a different way of handling data,” he says.
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Within Houdini, it becomes a non-destructive system that supports parallel work across departments rather than a linear handover of tasks. “It tends to optimise parallel workflow between departments instead of cascading workflows,” adds Selmi.
On Surviving Earth, that approach started early, with Unreal Engine used for previsualisation and environment building that would later feed directly into Milk’s 3D pipeline. “We effectively created these environments in Unreal that we inherited in our 3D workflow,” Selmi says.
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From there, those environments were imported into Houdini and structured as USD “stages,” which serve as full-scene containers for sequences or even entire projects. “The stage is your first file where you start storing data for the whole sequence or even the whole project.”
Because those stages are built from the outset, production doesn’t have to wait for traditional departments to finish in sequence. “It allowed us to start previewing our 3D work early on instead of waiting for an environment task or a creature task or a rigging task or an animation task,” reveals Selmi, before explaining how within each stage, work is split into layers, allowing multiple departments to move simultaneously within the same structure. “We could create layers. We could start working on the asset level […] we could already start the rigging phase and also the layout animation phase.”
That layering also changes how clients see work in progress, with sequences and edits able to be reviewed dynamically as they evolve. “We could dynamically previsualize to the client the evolution of the sequence and the evolution of the cut,” he says, but crucially, iteration doesn’t erase previous work: “It wasn’t necessarily a loss of data or a loss of work because we kept building up on the specific development. It would just replace what was done and approved by the client.”
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That continuity carries through to assets themselves, as Selmi explains: “A creature that was already pre-animated would carry on the final creature element and the look-dev element […] the animation itself was continued on the previous visualisation, so it wasn’t lost and something to redo.”
The Houdini and Maya mix
At the core of this system is referencing rather than fixed file structures. “It’s all about IDs. It’s all about referencing. It’s not about a hard path that needs to be cached and recached.” Selmi describes it as a kind of structured propagation through production. “You’re creating a flag – in this stage, we’re creating this placeholder for this specific asset, and it’s just going to trickle down every time it gets updated.”
Across Milk’s pipeline, USD is used alongside tools such as Houdini and Maya, with Solaris (Houdini's USD lighting layout setup) acting as a key environment for working on and preparing stages for final rendering. The structure itself is built around layered data, covering modelling, layout, animation, FX, and lighting, all of which can develop in parallel rather than sequentially. “We could dynamically previsualize for the client the evolution of the sequence and its edit,” Selmi says.
That parallel structure allows different stages of production to overlap in a way that wouldn’t normally be possible, with asset finalisation running alongside concept approval, and rigging and layout already underway while earlier work is still being refined. “We could start working on the 3D asset for its finalisation while using concept models for client approval, and concurrently begin rigging and layout animation, and also set up CG cameras.”
Because the system is non-destructive, updates simply replace earlier versions without breaking the underlying structure. “The new element or data would simply replace an earlier element version,” he explains.
For Selmi, the result of all this is as much organisational as it is technical, shifting where effort and budget go within a production. “There’s a lot of data to manage,” he says, “but I think this shifts a little bit the relationship with the client. Most of the budget doesn’t go on figuring out how to manage or encapsulate data, or solving problems, but it becomes more of a relationship of visual storytelling. There’s now more work at the beginning of a project, and you can really make a difference.”
So there you have it, the next time you see a monster crashing across the screen, or tune in to watch Surviving Earth on NBC, think about the systems, tech and workflows that go into making those creatures live. Visit Milk VFX for more insights.