The release announcement on the WebM blog. This is their second named release of the libvpx VP8 library. This releases focuses upon their SDK (Software Development Kit) and not their format specification.
With Bali, the best mode average encoding speed is 4.5x faster than the original VP8 library release, over 1.3x faster than the previous release, and is similarly faster with their "good" encoding settings. The encoding speed under ARM with Neon extensions is even much greater: 7% faster than the previous release with a Cortex A9, 15% faster with a dual-core ARM CPU, and 26% faster with a quad-core ARM CPU. The NVIDIA Tegra2 platform is also 21~36% faster.
VP8 Bali also improves the video quality, achieves more consistent high video quality, improved quality when dealing with noisy source videos, better predictions of motion vectors, various functions have added Assembly code or its rewritten, and there's multi-core processing improvements, especially for ARM platforms.