where to find fev file header?

just to clean up your assumption there

#ifdef FMOD_SUPPORT_PRAGMAPACK
#pragma pack(1)
#endif
struct FSB5_HEADER
{
char id[4]; // ‘FSB5’
unsigned int subVersion; // Extended FSB version
int numSubSounds; // Number of subsounds in the file
unsigned int headerChunkSizeBytes; // Size in bytes of all of the sub-sound headers including metadata
unsigned int namesChunkSizeBytes; // Size in bytes of all the original source file names
unsigned int dataChunkSizeBytes; // Size in bytes of compressed sample data
FMOD_FSB_FORMAT dataFormat; // Compression format
unsigned int dataFormatVersion; // Version number of compression format
unsigned int mode; // Flags that apply to all subsounds in the FSB
FMOD_UINT64 compatibilityHash; // Deprecated
FMOD_GUID guid; // MD5 hash based unique identifier using all header information
} FMOD_PACKED;
#ifdef FMOD_SUPPORT_PRAGMAPACK
#pragma pack()
#endif