SFM/Rendering in stereoscopic 3D
From Valve Developer Community
To render a given scene in stereoscopic 3D (side by side):
- After you finish your animation or picture click on File, click Export, click Movie..., or press the keyboard shortcut Ctrl+M.
- In the lower left corner of the Export Movie... window, select More Options > > >.
- Click the Layoff Settings tab.
- In the Stereoscopic row check the checkboxes Render Stereoscopic and Single File (side by side).
When you click Export Movie your scene will be rendered at the selected resolution and frame rate and the output will be stereoscopic 3D.
Note:If you want to export an image sequence in 3D you have to choose TGA as the output format. It's the only one that seems to work at this time.