Arcane University:File Compression for Xbox

This page details methods to reduce file size of assets so that a mod's total repository size more comfortably fits within the Xbox system mod space limitations. Credits go to Snipey360, who was invaluable in reducing Bruma's size on consoles from 3.8 gigabytes to 2.3 gigabytes.

Xbox Limitations

The most well known limitation imposed by Skyrim: Special Edition on Xbox consoles (Xbox One, Series X, and Series S) is the 5 GiB total mod limit. Additionally, the size of any single mod can be a maximum of 1 GiB. A mod's size consists of both its BSAs and .esm/.esp files. For this reason, when packing BSAs it is important to first consider the size of the .esm/.esp file it will be paired with. With large mods, repositories should be split to maximize the assets in each BSA that come with each .esm/.esp. Each mod may have two BSAs, a standard and a - Textures BSA. Dummy .esms may be needed to ensure that all BSAs are loaded, as bethesda.net requires that each BSA file has a corresponding .esm/.esp file with the same name. Xbox BSAs must be named with _xbox appended as a suffix (BSHeartlands_xbox.bsa and BSHeartlands_xbox - Textures.bsa, for example), but otherwise are identical to standard .BSA files. Renaming a .BSA file to add this suffix does not create issues with the file.

Not all Xbox limitations are bad news, however. Some of Xbox's other limitations can be used to the advantage of a mod author who wishes to minimize file size. For instance, Xbox versions of Skyrim play audio at 48kbps. As such, any files with higher quality audio will be automatically be reduced in quality when played in game. Thus, reducing quality to 48kbps is essentially a lossless way to reduce file size on the platform.