GoodReader User Manual
Audio & Video
GoodReader lets you listen to audio files and watch videos.
Only those formats are allowed that are natively supported by iOS.
For audio, these are the files with the following extensions: .aac, .adts, .ac3, .aif, .aiff, .aifc, .caf, .mp3, .m4a, .m4b, .snd, .au, .sd2, wav
For video, these are the known types: .mov, .mp4, .m4v, .3gp, .mpv
Audio player appears as a standalone popup control panel. It is accessible from the main screen, as well as from any file viewer, allowing you to listen to audio and control the playback while reading your documents. A single track or the entire contents of a folder can be played. Repeat and shuffle options are also supported.
Here's an additional information provided by Apple about supported video formats: