Add VAG struct

VAG.md

@@ -28,6 +28,25 @@ wav2vag tmp.dat output.vag -sraw16 -freq=44100
 
 You can find a graphical editor in the [PsyQ sdk](http://psx.arthus.net/sdk/Psy-Q/PSYQ_SDK.zip) named `VAGEDIT.exe`.
 
+## C VAG structure
+
+Here is a structure definition to access the VAG header :
+
+See [FileFormat47.pdf](http://psx.arthus.net/sdk/Psy-Q/DOCS/FileFormat47.pdf), p.209 for full description.  
+
+```c
+typedef struct VAGhdr {                 // All the values in this header must be big endian
+        char id[4];                     // VAGp         4 bytes -> 1 char * 4
+        unsigned int version;           // 4 bytes
+        unsigned int reserved;          // 4 bytes
+        unsigned int dataSize;          // (in bytes) 4 bytes
+        unsigned int samplingFrequency; // 4 bytes
+        char  reserved2[12];            // 12 bytes -> 1 char * 12
+        char  name[16];                 // 16 bytes -> 1 char * 16
+        // Waveform data after that
+} VAGhdr;
+``` 
+
 ## VAG & SPU Docs
 
 See