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PAK (Metroid Prime) (view source)

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Note that the Metroid Prime 3 E3 prototype uses this pak format as well, but has 64-bit file IDs. This is the only difference; the version number is still the same, so there isn't an easy way to check for this variation of the format.
Note that the Metroid Prime 3 E3 prototype uses this pak format as well, but has 64-bit file IDs. This is the only difference; the version number is still the same, so there isn't an easy way to check for this variation of the format.
{{researchminor
|reason = Some minor research is needed to figure out the optimal way to order files to optimize load times.
}}


__TOC__
__TOC__
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{| class="wikitable"
{| class="wikitable"
! Offset
! Offset
! Size
! Type
! Description
! Name
! Notes
|-
|-
| 0x0
| 0x0
| 4
| int16
| '''Version number'''. Always 0x00030005.
| '''Version Number Major'''
| Always 3
|-
| 0x2
| int16
| '''Version Number Minor'''
| Always 5
|-
|-
| 0x4
| 0x4
| 4
| int32
| '''Unused'''; always 0
| '''Unused'''
| Always 0
|-
|-
| 0x8
| 0x8
| colspan=2 {{unknown|End of header}}
| colspan=3 {{unknown|End of header}}
|}
|}


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{| class="wikitable"
{| class="wikitable"
! Offset
! Offset
! Size
! Type
! Description
! Count
! Name
! Notes
|-
|-
| 0x0
| 0x0
| 4
| {{FourCC}}
| '''File type''' fourCC.
| 1
| '''Asset Type'''
| Indicates the type of asset (texture, model, area, etc) and usually doubles as the asset's cooked file extension.
|-
|-
| 0x4
| 0x4
| 4
| int32
| '''File ID'''.
| 1
| '''Asset ID'''
| Unique identifier for this asset.
|-
|-
| 0x8
| 0x8
| 4
| int32
| '''Name length''' (NL)
| 1
| '''Name Length'''
| Length of the name string
|-
|-
| 0xC
| 0xC
| NL
| char
| '''Name'''; not zero-terminated
| ''Name Length''
| '''Name String'''
| Name of the asset. Not zero-terminated. This name usually corresponds to a hardcoded string that the game uses to look up the asset, so this generally can't be changed.
|-
|-
| 0xC + NL
| colspan=5 {{unknown|End of entry}}
| colspan=2 {{unknown|End of entry}}
|}
|}


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{| class="wikitable"
{| class="wikitable"
! Offset
! Offset
! Size
! Type
! Description
! Name
! Notes
|-
|-
| 0x0
| 0x0
| 4
| int32
| '''Compression flag'''; this will either be 0 or 1, with 1 denoting a compressed file.
| '''Compression Flag'''
| Value will be either 0 or 1, with 1 denoting that the asset is compressed.
|-
|-
| 0x4
| 0x4
| 4
| {{FourCC}}
| '''File type''' fourCC.
| '''Asset Type'''
| Indicates the type of asset (texture, model, area, etc) and usually doubles as the asset's cooked file extension.
|-
|-
| 0x8
| 0x8
| 4
| int32
| '''File ID'''
| '''Asset ID'''
| Unique identifier for this asset. This ID is used by other assets to reference this one.
|-
|-
| 0xC
| 0xC
| 4
| int32
| '''Size''' (note: always a multiple of 32. The end of the file is padded with 0xFF in order to be 32-byte aligned.)
| '''Size'''
| Size of the asset data in the pak. This is always 32-byte-aligned. The end of the asset is padded with 0xFF.
|-
|-
| 0x10
| 0x10
| 4
| int32
| '''Offset'''
| '''Offset'''
| Offset of the asset data within the pak. This is an absolute offset.
|-
|-
| 0x14
| 0x14
| colspan=2 {{unknown|End of entry}}
| colspan=4 {{unknown|End of entry}}
|}
|}


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* [[CRSC (File Format)|CRSC]]
* [[CRSC (File Format)|CRSC]]


Additionally, in Prime 2 any files can be left uncompressed if the compressed file is larger than the uncompressed one. This is not the case in Prime 1 (although custom repacking implementations should probably do this regardless).
Additionally, in Prime 2 any files can be left uncompressed if the compressed file is larger than the uncompressed one. This is not the case in Prime 1 (although custom repacking implementations should probably do this regardless, as there's no benefit to the compression in this scenario).
 
== Optimizing Load Times ==
 
When rebuilding new paks, it's extremely important that asset order be optimized in order to minimize the distance the game has to seek on the disc in order to load any given asset. A poorly optimized pak can easily have 30+ second load times on small rooms. There are three main things that are done in order to keep load times fast.
 
* In world paks, assets are often duplicated so they appear multiple times within the pak; if an asset is used by a lot of different areas this can help reduce seek distance, but has the downside of bloating the total file size of the pak. To ensure the best balance between the two, asset duplication was flagged on a per-area basis, as larger areas take longer to load and would benefit from the faster load speed, whereas small rooms tend to load quickly anyway even without duplicates. The flag that was used for this only existed in Retro's raw files and isn't present in the final game's cooked data. You can recreate it by analyzing the pak and noting down which rooms have duplicate assets (bearing in mind that the assets used by a room always precede that room's MREA asset). If you are working strictly from a pre-unpacked pak, you can't replicate the flag.
* Assets are generally grouped by load order - things that are used together are adjacent in the pak, and an asset's dependencies typically appear immediately preceding the asset itself. This grouping helps ensure that even when assets aren't duplicated the game will still be able to do just one large seek and then load a bunch of assets at once, instead of having to do a separate seek for each asset.
* Once you have assets stored in the pak in the right order, you need to make sure the game actually reads them in that order! The exact order that assets are loaded in is specified by the dependency list in the [[MLVL (File Format)|MLVL]] file; as such, the MLVL list should also have assets grouped in the same way and the same order and should at least roughly match the order files are positioned in the pak.


== File Order ==
For every asset loaded, the game checks every copy of the asset in the pak and loads whichever duplicate is the shortest distance from the last read position (the end of the last asset that was loaded). When loading an area, this is the order the game loads assets in:
* First the game goes down the area dependency list in the [[MLVL (File Format)|MLVL]] file and loads every file in the list for every active layer. The game follows the exact order specified by the list.
* After loading all area dependencies, the area itself is loaded.
* Finally the game loads assets being used by the new area that are missing from the list. This primarily means [[SCAN (File Format)|SCAN]] files (in MP1), the skybox model, and assets being used by PlayerActor animsets (this avoids loading PlayerActor assets for suits that the player doesn't have). If any other assets were missing from the list, they are loaded here. It's very important to know that contrary to the previous steps, assets that still aren't in memory at this point are loaded ''synchronously'', which means the game will hang until loading is complete; therefore, you want as few assets as possible to be left to load at this point. (You can observe this hang even in the base game - there is a small freeze towards the end of loading Artifact Temple.)
* Note that any assets that are already in memory will be skipped.


File order matters significantly and easily makes the difference between a pak loading quickly and optimally, or taking 30+ seconds on every door. While more research is required to figure out exactly how files should be ordered to optimize loading, the game generally clusters together resources that are used together, and a file's dependencies generally appear directly before the file itself. The game also often duplicates assets that are used multiple times within the same pak; there might be 10-11 copies of the same model file in order to allow the game to more easily find and load that file when it needs it.
'''Note:''' There are some discrepancies between the order assets appear in the pak and the actual load order specified by the MLVL file. There might be some more research needed to fully explain all the quirks behind Retro's pak optimization.


== Tools ==
== Tools ==


* [https://drive.google.com/file/d/0B9MLV21H7SDvcGc1QjRfSTFJNk0/view?usp=sharing PakTool] by Parax
* [https://www.dropbox.com/s/bba2n9jzj719by4/PakTool.rar?dl=0 PakTool] by Aruki


[[Category:File Formats]]
[[Category:File Formats]]
[[Category:Metroid Prime]]
[[Category:Metroid Prime]]
[[Category:Metroid Prime 2: Echoes]]
[[Category:Metroid Prime 2: Echoes]]
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