In a video posted on July 21, 2009, YouTube software engineer Peter Bradshaw announced that YouTube users can now upload <answer>3D</answer> videos. The videos can be viewed in several different ways, including the common anaglyph (cyan/red lens) method which utilizes glasses worn by the viewer to achieve the <answer>3D</answer> effect. The YouTube Flash player can display stereoscopic content interleaved in rows, columns or a checkerboard pattern, side-by-side or anaglyph using a red/cyan, green/magenta or blue/yellow combination. In May 2011, an HTML5 version of the YouTube player began supporting side-by-side <answer>3D</answer> footage that is compatible with Nvidia <answer>3D</answer> Vision.
What type of videos did youtube officially start supporting in July 2009?
3D