SPC

SPC is an audio format for playing native SNES audio.

SPC File Format

Offset Size Description
00000h 33 File header "SNES-SPC700 Sound File Data v0.30"
00021h 2 0x26, 0x26
00023h 1 0x26 = Header Has ID666 Information<br/>0x27 = Header Has No ID666 Tag
00024h 1 Version Minor (i.e. 30)
SPC700 Registers 00025h 2 PC
SPC700 Registers 00027h 1 A
SPC700 Registers 00028h 1 X
SPC700 Registers 00029h 1 Y
SPC700 Registers 0002Ah 1 PSW
SPC700 Registers 0002Bh 1 SP (Lower Byte)
SPC700 Registers 0002Ch 2 Reserved
ID666 Tag (Text Format) 0002Eh 32 Song Title
ID666 Tag (Text Format) 0004Eh 32 Game Title
ID666 Tag (Text Format) 0006Eh 16 Name of Dumper
ID666 Tag (Text Format) 0007Eh 32 Comments
ID666 Tag (Text Format) 0009Eh 11 Date SPC was Dumped (MM/DD/YYYY)
ID666 Tag (Text Format) 000A9h 3 Number of Seconds to Play Song before Fading Out
ID666 Tag (Text Format) 000ACh 5 Length of Fade in Milliseconds
ID666 Tag (Text Format) 000B1h 32 Artist of Song
ID666 Tag (Text Format) 000D1h 1 Default Channel Disables<br/>0 = Enable<br/>1 = Disable
ID666 Tag (Text Format) 000D2h 1 Emulator used to dump SPC<br/>0 = Unknown<br/>1 = ZSNES<br/>2 = Snes9x
ID666 Tag (Text Format) 000D3h 45 Reserved (Set to 0x00)
ID666 Tag (Binary Format) 0002Eh 32 Song Title
ID666 Tag (Binary Format) 0004Eh 32 Game Title
ID666 Tag (Binary Format) 0006Eh 16 Name of Dumper
ID666 Tag (Binary Format) 0007Eh 32 Comments
ID666 Tag (Binary Format) 0009Eh 4 Date SPC was Dumped (YYYYMMDD)
ID666 Tag (Binary Format) 000A2h 7 Unused
ID666 Tag (Binary Format) 000A9h 3 Number of Seconds to Play Song before Fading Out (Numeric string)
ID666 Tag (Binary Format) 000ACh 5 Length of Fade in Milliseconds (Numeric string)
ID666 Tag (Binary Format) 000B1h 32 Artist of Song
ID666 Tag (Binary Format) 000D1h 1 Default Channel Disables<br/>0 = Enable<br/>1 = Disable
ID666 Tag (Binary Format) 000D2h 1 Emulator used to dump SPC<br/>0 = Unknown<br/>1 = ZSNES<br/>2 = Snes9x
ID666 Tag (Binary Format) 000D3h 45 Reserved (Set to 0x00)
00100h 65536 64KB RAM
10100h 128 DSP Registers
10180h 64 Unused
101C0h 64 Extra RAM (Memory Region used when the IPL ROM region is set to read-only)
10200h Extended ID666

Extended ID666 Format

Extended information is stored at the end of the SPC file as a RIFF chunk with an ID of xid6. Items that can be stored in the ID666 tag without any loss of data should not be stored in the extended area.

Offset Size Description
0 4 Chunk type, ie xid6
4 4 Chunk size, not including header

Sub-Chunk Header

Inside the chunk are sub-chunks. Each sub-chunk consists of a 4-byte header, and possibly data. All data is 32-bit aligned. If the data stored doesn't reach a 32-bit boundary, it will be padded with 0's.

Offset Size Description
0 1 ID: Song Name, Length, etc.
1 1 Type<br/>0 = Data is stored in the header<br/>Non-Zero = data is stored after header
2 2 Data<br/>If 'Type' = Zero, this contains the data<br/>If 'Type' is non-zero, this contains the length of the data following the header

Extended ID666 Items

ID:   00-0F - Items from original ID666 tag
      10-1F - Extended items
      30-3F - Items related to playback

Type: 00 Data    - Data is saved in the 'data' item of the sub-chunk header.
      01 String  - Data is stored as a null terminated string (max 256 characters including null). 
                   Strings are saved using 8-bit character encoding.
                   Support for unicode may be added in the future.
      04 Integer - Data is stored as a 32-bit integer.

Size: The minimum and maximum sizes of an item.

ID Type Size Description
01h String 4-256 Song Name
02h String 4-256 Game Name
03h String 4-256 Artist's Name
04h String 4-256 Dumper's Name
05h Integer 4 Date Song was Dumped (stored as YYYYMMDD)
06h Data 1 Emulator Used
07h String 4-256 Comments
10h String 4-256 Official Soundtrack Title
11h Data 1 OST Disc
12h Data 2 OST Track (upper byte is the number 0-99, lower byte is an optional ASCII character)
13h String 4-256 Publisher's Name
14h Data 2 Copyright Year
30h Integer 4 Introduction Length (lengths are stored in 1/64000th seconds)
31h Integer 4 Loop Length
32h Integer 4 End Length
33h Integer 4 Fade Length
34h Data 1 Muted Voices (a bit is set for each voice that's muted)
35h Data 1 Number of Times to Loop
36h Data 1 Mixing (Preamp) Level

Lengths are stored in ticks. A tick is 1/64000th of a second. The maximum length is 383999999 ticks. The End can contain a negative value.

This may seem like a messy way to implement a format, but I wanted to assure something that would be easily expandable. The source code to SNESAmp contains a C++ class for reading and writing ID666 and xid6 tags.

Addendum

  • Fixed the number of reserved bytes at offset 0002Ch
  • Changed the version number to v0.31
  • Detecting the format of the SPC file (binary or text) can be a bit tricky, since fields might contain ambiguous values and there's no format indicator. Some fields have different offsets depending of the format, which might help with the detection. The current Win32 version of ZSNES saves binary SPC files; SNES9x saves in text format.

RSN

RSN is a packed/grouped format for SPC files.

Solid Archives

Often, SPC files will only differ by a few KB, with the rest bit-identical. For example, several songs might all use the same playback code and set of samples, with only the module data (or even just the playback pointer) differing between songs. But because PKZIP always compresses each file as a separate object, it can't take advantage of similarities between files. Even tar.gz, which combines the files before compressing them into a "solid archive", could only reference data from the past 32768 bytes. RAR was the first widely used general data compression program that used a window bigger than a single SPC file, so SPC sets were often distributed as RAR files.

Why Specifically RAR

The one disadvantage of RAR is that it is not free software due to a license term prohibiting reverse-engineering the format to create a description of the compression method:

The UnRAR sources may be used in any software to handle RAR archives without limitations free of charge, but cannot be used to re-create the RAR compression algorithm, which is proprietary. Distribution of modified UnRAR sources in separate form or as a part of other software is permitted, provided that it is clearly stated in the documentation and source comments that the code may not be used to develop a RAR (WinRAR) compatible archiver.

7-Zip and tar.bz2 are free alternatives to RAR, but RAR had the first mover advantage, and music archives that already deal in non-free music have seen no need to repack in a free format.

Why the Rename to RSN

Windows Explorer (the file manager in Windows) uses the part of the filename after the last period character ("the extension") to determine file type. That's why various file formats based on PKZIP archives have different extensions: .zip for general data, .jar for Java applications, .smzip for StepMania, .cbz for sequences of JPEG or PNG images ("comic book zip"), .odt for OASIS text documents, .ods for OASIS spreadsheets, etc. Likewise, RAR has .rar for general data, .cbr for image sequences, and .rsn (RAR Super Nintendo) for sets of SPC files.

The first player to support RSN files was Winamp, which does not support playing files from archives in general. Input plug-ins for archives exist; they unpack an archive's contents to a temporary folder and then open the resulting files with the correct input plug-in.

Players such as foobar2000 do not require the RSN hack since the player itself can support RAR files directly. Of course, you probably don't want to associate RAR files with the audio player, but you can still drag the archives onto the player, as well as open them within the player, and they can contain more than just SPC files. Although most general purpose audio formats are already compressed, so they don't really benefit from being stuffed into other archive formats.

RSN Descriptions written by [[Tepples]] and [[kode54]]

SPC File Format v0.31 by creaothceann, 2006-02-27 21:48