Vista Codec Package is a software that allows users to play various multimedia formats on their Windows Vista operating system. It includes a range of codecs, filters, and splitters that enable playback of popular video and audio formats such as AVI, MP4, MKV, and FLAC. The software also features a media player classic, which provides additional playback options and customization settings. Lastly, the Vista Codec Package offers support for subtitles and allows users to adjust video quality and audio settings.