There are two different types of PAK files used by the Modern Warfare series, Packfiles and Imagefiles. Packfiles store audio data and Imagefiles store image data.
Uses the same common header as all fastfiles do. After the header is nothing else but the data.
|Version||0x4||See fastfile versions|
On PS3, the compression method is the same as it is for fastfiles. Image data is concatenated as one file, split into blocks each 0x10000 bytes, then each block is compressed, and appended to the file.
On XBOX, each image's data is compressed, then appended to the file.
No image headers are stored in these files. It is currently unknown how they are loaded.
|Alignment||0x4|| PS3: 0x7FC|
After the header is the audio data. Each audio file is concatenated and aligned (by 0x800 on PS3). These sounds are known as streamed sounds. They are loaded through sound alias list assets by offsets.