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The BCSAR (CTR Sound ARchive) format is the 3DS's equivalent of the Wii's BRSAR format. They're not the same structures, though, but they do have the same purpose.

BCSAR are located in the RomFS, this is usually stored under "romfs:/sound/<name>.bcsar". This contains various audio formats, such as CSTM, CWSD, and CWAV.

BCSAR Header

0x0 0x4 MAGIC "CSAR"
0x4 0x2 Byte order mark (0xFEFF = Big Endian, 0xFFFE = Little Endian)
0x6 0x4 Length of BCSAR header
0xA 0x2 Version
0xC 0x4 Length of the entire BCSAR (starting from 0x0)
0x10 0x4 Amount of main partitions in the BCSAR [STRG + INFO + FILE = 0x03 (= 3)]
0x14 0x4 Partition header length [same for each partition? (ie STRG,INFO,and FILE header lengths)]
0x18 0x4 Location of STRG partition
0x1C 0x4 Length of STRG partition
0x20 0x4 Unknown (always 0x01200000?)
0x24 0x4 Location of INFO partition
0x28 0x4 Length of INFO partition
0x30 0x4 Location of main FILE partition
0x34 0x4 Length of main FILE partition
0x38 0x4 Reserved for 4th main partition location?
0x3C 0x4 Reserved for 4th main partition length?



STRG contains the names of the audio files in the BCSAR.


0x0 0x4 MAGIC "STRG"
0x4 0x4 Length of STRG partition (also in CSAR header)
0x18 0x4 Count of audio names (since each file should have a name you could also say this is essentially a file count)

Then for each name:

0x0 0x4 Type of the file...?
0x4 0x4 Offset of the filename...?
0x8 0x4 Size of the filename

Then every filename is rawly setted. You can set up a dictionary that contains, using a simple counter, the size of every filename in order. Then, using the same type of counter, get the values of the size of the filename in a correct order.


INFO presumably contains information on the audio files? Possibly used to connect names from STRG to data from FILE?

For now I only know some information in the header for this partition, but I'm working on figuring the rest out.

0x0 0x4 MAGIC "INFO"
0x4 0x4 Length of INFO partition (also in CSAR header)


FILE contains all of the audio data in the BCSAR.

0x0 0x4 MAGIC "FILE"
0x4 0x4 Length of FILE partition (also in CSAR header)

There isn't a whole lot else I can document about the FILE partition, since the data in it will most definitely vary depending on the game. (since audio is more than likely to change in each game)

There is no table in FILE so a different partition (presumably INFO) must be used to connect the data in FILE with the names from STRG.

After some more research, there are multiple FILE partitions, but only 1 of them is the 'main' FILE partition (it's the one you get from the BCSAR header). The 'main' FILE partition contains all of the other sub FILE partitions.