Overview
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
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x4 | MAGIC "CSAR" |
| 0x4 | 0x2 | Byte order mark (0xFEFF = Big Endian, 0xFFFE = Little Endian) |
| 0x6 | 0x2 | Length of BCSAR header |
| 0x8 | 0x4 | 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? |
Partitions
STRG
STRG contains the names of the audio files in the BCSAR.
Header
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x4 | MAGIC "STRG" |
| 0x4 | 0x4 | Length of STRG partition (also in CSAR header) |
| 0x8 | 0x4 | String table type magic (always 0x2400) |
| 0xC | 0x4 | This + 8 points to the string table (always 0x10) |
| 0x10 | 0x4 | String table lookup type magic (always 0x2401) |
| 0x14 | 0x4 | This + 8 points to the string lookup table |
| 0x18 | 0x4 | Filename count |
| 0x1C | 0xC * count | String offset table |
String offset table entry
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x4 | Type of the node (should be 0x1F01) |
| 0x4 | 0x4 | Offset to data from the end of the STRG header (sizeof 0x18) |
| 0x8 | 0x4 | Length of the data buffer (includes NUL terminator) |
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.
String lookup table
Header
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x4 | Index of the root entry |
| 0x4 | 0x4 | Entry count |
| 0x8 | 0x14 * count | Lookup entry |
Entry
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x2 | Is 1 if contains data |
| 0x2 | 0x2 | Unknown |
| 0x4 | 0x4 | Next index? (-1 if invalid) |
| 0x8 | 0x4 | Data index? (-1 if invalid) |
| 0xC | 0x8 | Unknown data, -1 if contains no data |
INFO
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.
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x0 | 0x4 | MAGIC "INFO" |
| 0x4 | 0x4 | Length of INFO partition (also in CSAR header) |
| 0x8 | 0x4 | Unknown magic 0x2100 |
| 0xC | 0x4 | This + 8 points to unknown |
| 0x10 | 0x4 | Unknown magic 0x2104 |
| 0x14 | 0x4 | This + 8 points to unknown |
| 0x18 | 0x4 | Unknown magic 0x2101 |
| 0x1C | 0x4 | This + 8 points to unknown |
| 0x20 | 0x4 | Unknown magic 0x2103 |
| 0x24 | 0x4 | This + 8 points to unknown |
| 0x28 | 0x4 | Unknown magic 0x2105 |
| 0x2C | 0x4 | This + 8 points to unknown |
| 0x30 | 0x4 | Unknown magic 0x2102 |
| 0x34 | 0x4 | This + 8 points to unknown |
| 0x38 | 0x4 | Unknown magic 0x2106 |
| 0x3C | 0x4 | This + 8 points to unknown |
| 0x40 | 0x4 | Unknown magic 0x220B |
| 0x44 | 0x4 | This + 8 points to unknown |
FILE
FILE contains all of the audio data in the BCSAR.
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 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.
Tools
- vgmtoolbox's Advanced Cutter/Offset Finder tool can extract BCWAVs without filenames