Editing BSA Files

==Description==
Almost all of the '''assets''' the game uses, such as textures, meshes, sounds, and so on, are stored in the .bsa files that can be found in the /Data/ folder.  These are [http://en.wikipedia.org/wiki/Archive_file archive files], similar to .zip files, but require specialized programs to open or create (see Tools Section).  Files in the .bsa are stored in a directory tree, and in order to get the game to recognize new files that replace existing files, they must be placed in the same place in the directory structure in the /Data/ folder, as the location of the original file within the .bsa file.

== Using existing assets with the GECK ==
Some records in the GECK have fields, such as model or texture paths, that point to files that are stored in the .bsa files.  The file path listed will show the location of the file in the directory structure within the .bsa file.  When you try to change one of these, the GECK will try to open the ''actual folder'' in your /Data/ folder.  In order to select an existing asset for the field you are trying to edit, you will have to extract that file from the .bsa it's contained in, and place it in the matching place in the /Data/ folder.

== Using new assets with new BSA files ==
===Notes===
It is possible to create new BSA files in order to distribute new assets with user-created mods.  This has benefits and drawbacks:
* Easy installation
** Users will only have to install two files: the .esp file for your mod, and the .bsa file with the assets, which can simply be placed in the /Data/ folder.
* Changing things is harder
** Since your files are in a BSA file, editing a file, such as for texturing, will be harder, since the user will have to extract that from the BSA file first.  Depending on the mod, this may be preferable or not.
* Less fragmentation
** Fallout 3 mods can contribute majorly to [http://en.wikipedia.org/wiki/File_system_fragmentation file system fragmentation].  This is often caused by very large numbers of small files.  If you have a large mod with a hundred or more assets to go with it, fragmentation can be avoided by putting those assets in BSA files.

===Use===
It's generally best to put files in a .bsa just before releasing a mod, as working on a mod while the assets are in a .bsa can be frustrating.  When you're ready to put the files in the BSA, use one of the tools below.  You'll need to make sure the files are in the proper directory structure, so if you have a texture in /Data/Textures/Weapons/, it should show up in /Textures/Weapons/ in the bsa file (note that '''/Data/''' is not included).

There are two ways to get the game engine to recognize your new .bsa files:
* The first is to simple match the filename to the name of your .esp.  So if your mod is named '''JunkyMod.esp''', name your BSA file as '''JunkyMod.bsa'''.  The game will automatically look for assets from the .esp in the .bsa.
* The above method doesn't work for .esm files (see [[:Category:Data Files|Master Files]]), so there is a second method to use.  If your mod is named '''JunkyMod.esm''', you will want to create an empty .esp file (just open the GECK without loading anything and click save), and name it '''Junkymod.esp'''.  Then name your BSA file as '''JunkyMod - Assets.bsa'''.  You can change '''Assets'' to whatever you like, as long as the name of the .esm file is included at the beginning of the name of the .esp file.  This will trick the engine into looking up the assets for the .esm file in the appropriate BSA file.

== ArchiveInvalidation ==
This is a term used to describe how to get the game to recognize certain new files placed in the /Data/ folder.  You can read more about it [http://devnull.devakm.googlepages.com/archiveinvalidation here.]  That page is specifically for Oblivion, but mostly applies to Fallout 3 as well.

==Tools==
You can view, edit, and create BSA files with the following tools:
*[[FOMM]]
*[[FO3 Archive]]

[[Category:Data Files]]
[[Category:Advanced_Modding_Techniques]]