Tears of Steel is a short science-fiction film from the Blender Foundation, released in 2012. It mixes live-action footage, shot in Amsterdam, with computer-generated robots and effects, and it was made to push the free 3D software Blender into visual-effects work.

What makes it unusual is not the story but the openness. The finished film is released under a Creative Commons Attribution licence, so anyone may share and show it, and the team published their production files too: the footage, models and scenes behind every shot.

That turned a short film into a teaching tool. Students and studios have used its material to practise tracking, compositing and lighting on real footage, something that is usually locked away behind contracts.

It is twelve minutes long. Watch it once for the story, and a second time for the seams you cannot find.