Blu-ray compatibility can be useful when striving for cross device compatibility, especially in the realm of high definition hardware media players. The default x264 preset chooses adequate compatibility for Blu-ray players but it is now possible to choose more complex conversion settings while simply maintaining compatibility by explicitly enabling Blu-ray compatibility mode. However, it was up to the user to choose appropriate conversion settings. x264 has always had the ability to create video streams that are playable on most Blu-ray devices.
In April 2010, the x264 project announced full Blu-ray compliant video encoding capability making x264 the first free Blu-ray compliant software H.264 encoder. Motion vectors are restricted so that blocks on one side of the refresh column don't reference blocks on the other side, effectively creating a demarcation line in each frame. The video is still seekable: a special header, called the SEI Recovery Point, tells the decoder to "start here, decode X frames, and then start displaying the video." This hides the refresh effect from the user while the frame loads.
In effect, instead of a big keyframe, the keyframe is "spread" over many frames. Periodic Intra Refresh can replace keyframes by using a column of intra blocks that move across the video from one side to the other, thereby "refreshing" the image. X264 is able to use Periodic Intra Refresh instead of keyframes, which enables each frame to be capped to the same size enabling each slice to be immediately transmitted in a single UDP or TCP packet and on arrival immediately decoded.
X264 has SIMD assembly code acceleration on x86, PowerPC (using AltiVec), and ARMv7 (using NEON) platforms.
The complexity is measured using a combination of sum-of-squares optimization (SSD) and sum of absolute transformed differences (SATD).