pcm音量计算

int pcm_db_count(const unsigned char* ptr, size_t size)
{
int ndb = 0;

short int value;

int i;
long v = 0;
for(i=0; i<size; i+=2)
{
memcpy((char*)&value, ptr+i, 1);
memcpy((char*)&value+1, ptr+i+1, 1);
v += abs(value);
}

v = v/(size/2);

if(v != 0) {
ndb = (int)(20.0*log10((double)v / 65535.0 ));
}
else {
ndb = -96;
}

return ndb;
}