The 3ivx decoder plays back most MPEG-4 variants (including DivX 3,4 and 5, Apple MPEG-4, Philips MPEG-4 and XviD). The 3ivx decoder produces noticeably higher quality video than other decoders due to its high quality post-processing filters, and because of its core design and optimization maintains a record-breaking decode speed. The windows version of the decoder includes an AAC audio decoder for Windows Media Player as well as a Media Splitter (to play back .avi, .mov and .mp4 files inside Windows Media Player). <p>The 3ivx encoder produces industry-leading compact high quality MPEG-4 video and is distributed as a plug-in for QuickTime as well as a plug-in for Video for Windows. This allows you to encode MPEG-4 video in .avi, .mov or .mp4 files (with AAC audio) with the encoding application of your choice.