Type 4 : Marker

 ┌────┬──┬──┬──┬───┬───┐
 │ 04 │ BLKLEN │ MARKER│
 └────┴──┴──┴──┴───┴───┛

 This is a special sub-block that specifies a Marker (MARKER, 2 bytes) in
 the voice data.

 During voice output, the CT-VOICE driver updates the status word
 ct_voice_status with this marker value. Your program may check for the
 desired MARKER value to perform synchronization with the voice output
 process.

 The Marker value must be within the range of 1 to 0FFFE hex. Note that 0
 and FFFF hex are reserved by the CT-VOICE driver. Also refer to the
 following section Essentials of using the CT-VOICE driver.

 The BLKLEN field is always set to 2.