I would like unpack .bsa and repack without compress for improve performance (.bsa files have 100% compression, meshes .bsa is 1,4GB default and unpack are 2,8GB) but I tried do it with FOMM and skyrim crashed on startup with .bsa files decompressed with FOMM. Anyone know .bsa tool working on Skyrim .bsa files? or we need waiting for new tools for Skyrim?

Sorry for my bad english

Use a hex editor. FOMM sets the 5th bit to 67 and the 14th bit to 07. They should be 68 and 00, respectively, for Skyrim. Can't comment on whether uncompressing is actually worthwhile though.

Least I think its the 14th bit...either way, change whatever bit is 07 to 00, in the first line.

http://www.physics.ohio-state.edu/~prewett/hexedit/

Honestly, one should never modify the default BSAs.
Extract the assets out, modify them, then drop them in the data folder in the correct directory structure and use archive invalidation to load them as overrides.

I won't modify files, i would like unpack .bsa files only and repack without compress for FPS performance as oblivion.

Have your tried using OBMM or FOMM?

Just move the BSA to a temp directory, back them up too.

Make sure to note the file date on them and then use a tool to redate them to that.

I'm curious how much compression are on them and which ones too.

Yes, I tried with FOMM and crash the game on startup, compress is 100% (meshes .bsa is 1.4GB and unpack is 2,8GB)

I promise, my solution in the first reply is why the game is crashing. I had the same problem. .bsa files for Oblivion and Fallout have a different file header then .bsa files for Skyrim. When you repack a .bsa with FOMM it assumes you're making a .bsa for Fallout, so it sets the headers for fallout. Skyrim tries to access what it sees as a fallout archive, and explodes. Just change the header bytes manually, problem solved. You can just open the mesh.bsa that you originally unpacked to see what the bytes should be, if you didnt follow exactly which ones to change.

You are not allowed to surpass 2GB AFAIK.

I know this and with .bsa animation unpack and repack only again (44MB compressed and 88MB decompressed) also crash on startup :S

Yes, you are right. Algorithm for .bsa files on Skyrim is diferent and with hex editor would work. Thx for reply xD

You could try http://obge.paradice-insight.us/wiki/NIFopt_%28GUI%29, use the "copy"-option. This all develops so fast I haven't even run the game yet. I only compared the BSA-headers and in theory they should be fine. I appreciate feedback.

Is archive invalidation necessary again with the 'new' engine?

This is not correct. People have unpacked and PyFFI'd the vanilla Oblivion meshes, then repacked them as BSAs and have got significant performance increases. Just be sure to make back ups.

BSAs generally load faster than loose files too. Or at least they have done for previous games.

If they come out to over two gigs once uncompressed then perhaps the same method as with Oblivion is needed: To register the extra BSA in the ini file.

It isnt with interface files. Just plop the files in Data/Interface, and Skyrim uses the nice new fonts. Havent tried anything else, been pretty obsessed trying to get a UI I like.

Redundancy report (best compression possible, duplicate linking):

Skyrim - Animations.bsa    42365780 ->   40168160 (1133 duplicates) 94.8%Skyrim - Interface.bsa     34608945 ->   14150057 (9 duplicates) 40.9%Skyrim - Meshes.bsa      1520899887 -> 1482423428 (34 duplicates) 97.5%Skyrim - Misc.bsa         177894975 ->  132840928 (453 duplicates) 74.7%Skyrim - Shaders.bsa       25686897 ->    1621781 (0 duplicates) 6.3%Skyrim - Sounds.bsa       953785521 ->  741773824 (42 duplicates) 77.8%Skyrim - Textures.bsa    1388866502 -> 1344588359 (6178 duplicates) 96.8%Skyrim - Voices.bsa      1458554685 -> 1293664414 (761 duplicates) 88.7%Skyrim - Voicesixtra.bsa   13016190 ->   11614402 (7 duplicates) 89.2%

Edit: BSAs produced by NIFopt work fine.