This refers to the audio format. AC3 is the file extension for Dolby Digital , a technology that supports 5.1 surround sound, providing an immersive home theater experience. Viewing Experience
This indicates Full HD resolution (1920x1080) using the H.264 codec. It provides a crisp, clear image with efficient file sizing, ensuring that the lush jungles of Pandora aren't lost in a sea of pixelated artifacts. Avatar -2009- 3D-HSBS-1080p-H264-AC 3 -DolbyDig...
Here is what the technical tags tell you about the quality and format: This refers to the audio format