Android Question How to read and write external storage through RandomAccessFile

    Dim FileName As String
   Dim Dir As String
   ' this path is for test
   Dir = "/storage/7764832/test"
   FileName = "v.mp4"
   
   Dim buffer1(256) As Byte
   
   Dim raf As RandomAccessFile
   ' error for this line
   raf.Initialize(Dir, FileName, False)
   raf.ReadBytes(buffer1, 0, buffer1.length,0)
   
   raf.Close

this is error
java.io.FileNotFoundException: /storage/7764832/test/v.mp4: open failed: EACCES (Permission denied)