This paper examines the evolution, technical challenges, and modern solutions for playing Xvid-encoded content on the iPad.
The native "Videos" or "TV" apps are programmed to ignore containers like .avi or .mkv which frequently house Xvid streams.
This player provides a premium experience by combining wide codec support with a metadata-rich interface, often cited by reviewers at Macworld as the gold standard for iPad media consumption.
Abstract
Perhaps the most notable solution, VLC for iOS uses an open-source engine to decode almost any codec, including Xvid, directly on the iPad.