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VGS BGM Decoder

  • decodes: VGS's .BGM file to PCM
  • platform free

License

The BSD 2-Clause License

How to use

  • Create Context
  • Load BGM data (from file or memory)
    • Get Meta Information (optional)
    • Decode
    • Get/Set Register (optional)
  • Release Context

Create Context

prototyping

void* vgsdec_create_context();

return value

  • !NULL : context
  • NULL : error

Load BGM data

prototyping

int vgsdec_load_bgm_from_file(void* context, const char* path);
int vgsdec_load_bgm_from_memory(void* context, void* data, size_t size);

arguments

  • context : context
  • path : path of the .BGM or .vgs file
  • data : pointer of memory area that BGM or .vgs file data stored.
  • size : size of the .BGM or .vgs file

return value

  • 0 : success
  • -1 : failed

Get Meta Information

prototyping

struct VgsMetaHeader* vgsdec_get_meta_header(void* context);
struct VgsMetaData* vgsdec_get_meta_data(void* context, int index);

arguments

  • context : context
  • index : index of the meta data

return value

  • NULL: if meta header or data is not exist.
  • !NULL: meta header or data

Decode (BASIC)

prototyping

void vgsdec_execute(void* context, void* buffer, size_t size);

arguments

  • context : context
  • buffer : stores decoded PCM data
  • size : size of buffer

remarks

  • this function stores decoded PCM data to the buffer.
  • The format of the PCM are fixed by the following:
    • sampling rate: 22050Hz
    • bit rate: 16bit
    • channels: 1 (monoral)
  • ex: 1 second = 44100 byte (22050 * 16 * 1 / 8)
  • use to sequentially call

Decode (ASYNC)

Async decoder function provides only for the senior programmer that fully understanding both of multiple threading mechanism and vgsdec.c. Please DO NOT USE, if you cannot the both or the either.

prototyping

int vgsdec_async_start(void* context);
int vgsdec_async_enqueue(void* context, void* buffer, size_t size, void (*callback)(void* context, void* buffer, size_t size));
void vgsdec_async_stop(void* context);
  • vgsdec_async_start function
    • start async decoder thread
  • vgsdec_async_enqueue function
    • enqueue a decode task
  • callback function:
    • called by async decoder thread after decoded.
  • vgsdec_async_stop function
    • stop async decoder thread

arguments

  • context : context
  • buffer : input/output buffer
  • size : size of buffer
  • callback : function pointer of callback after decoded

return value

  • 0 : success
  • -1 : failed

remarks

  • you must not call vgsdec_execute while running async decoder thread.

Get/Set Register

prototyping

int vgsdec_get_value(void* context, int type);
void vgsdec_set_value(void* context, int type, int value);

arguments

  • context : context
  • type : register type
  • value : register value

return value

  • register value

type

define get set description
VGSDEC_REG_KEY_{0~5} o - get the scale value of Ch{0~5}
VGSDEC_REG_TONE_{0~5} o - get the tone value of Ch{0~5}
VGSDEC_REG_VOL_{0~5} o - get the average volume of Ch{0~5}
VGSDEC_REG_PLAYING o - current playing status: 0 = not playing, 1 = playing
VGSDEC_REG_INDEX o - get the playing note-index
VGSDEC_REG_LOOP_INDEX o - get the note index of the loop-label (acyclic song: -1)
VGSDEC_REG_LENGTH o - get the count of the notes
VGSDEC_REG_TIME o o get or set the playing time (1sec = 22050)
VGSDEC_REG_LOOP_TIME o - get the time of the loop-label (1sec = 22050)
VGSDEC_REG_TIME_LENGTH o - get the time-length (1sec = 22050)
VGSDEC_REG_LOOP_COUNT o - get the loop-count
VGSDEC_REG_RESET - o set none-zero: reset to the state after loading the data.
VGSDEC_REG_FADEOUT - o set none-zero: start fadeout.
VGSDEC_REG_FADEOUT_COUNTER o - get fadeout counter
VGSDEC_REG_VOLUME_RATE_{0~5} o o get or set the channel volume rate (0~100)
VGSDEC_REG_VOLUME_RATE o o get or set the master volume rate (0~100)
VGSDEC_REG_SYNTHESIS_BUFFER o o set none-zero: does not clear the buffer when called vgsdec_execute
VGSDEC_REG_KEYON_{0~5} o - get key-on status of Ch{0~5}: 0 = key-off, 1 = key-on
VGSDEC_REG_MUTE_{0~5} o o get or set the mute of Ch{0~5}: 0 = sound, 1 = mute
VGSDEC_REG_ADD_KEY_{0~5} o o get or set the scale up/down of Ch{0~5}
VGSDEC_REG_KOBUSHI o o get or set the Kobushi mode: 0 = not kobushi, 1 = kobushi

scale value

Octave A A# B C C# D D# E F F# G G#
0 0 1 2 3 4 5 6 7 8 9 10 11
1 12 13 14 15 16 17 18 19 20 21 22 23
2 24 25 26 27 28 29 30 31 32 33 34 35
3 36 37 38 39 40 41 42 43 44 45 46 47
4 48 49 50 51 52 53 54 55 56 57 58 59
5 60 61 62 63 64 65 66 67 68 69 70 71
6 72 73 74 75 76 77 78 79 80 81 82 83
7 84 - - - - - - - - - - -

scale up/down

  • set VGSDEC_REG_ADD_KEY = 5: C major -> F major
  • set VGSDEC_REG_ADD_KEY = -1: C major -> B major
  • please exclude rhythm channel (but specific rhythm channel is impossible...)

tone value

value name
0 Sin wave
1 Square ware
2 Saw wave
3 Noize wave

fadeout counter

means of counter value
  • 0 : noop
  • 1 ~ 99 : in-progress
  • 100 : finished
mechanism
  • set VGSDEC_REG_FADEOUT --> VGSDEC_REG_FADEOUT_COUNT to be 1
  • VGSDEC_REG_FADEOUT_COUNT increments per 1024Hz (about 0.04643990929705 seconds) , if not 0 or 100
  • VGSDEC_REG_FADEOUT_COUNT equals 100 --> VGSDEC_REG_PLAYING to be zero

Release Context

prototyping

void vgsdec_release_context(void* context);

arguments

  • context : context

Build

example decoder

$ cd example
$ make

DLL (Windows only)

# nmake /f makedll.mak