std_callback
if (NULL != dev->ext_vv_data->std_callback)
dev->ext_vv_data->std_callback(dev, vv->standard);
.std_callback = &std_callback,
.std_callback = &std_callback,
.std_callback = &std_callback,
.std_callback = &std_callback,
.std_callback = &std_callback,
int (*std_callback)(struct saa7146_dev*, struct saa7146_standard *);