Why does it take time to write data to DVD writable media?

• In disc-at-once mode, it may take about 20 to 40 minutes to complete the writing process after the progress bar reaches 100%. This is normal and does not indicate a malfunction, so wait until the process is complete.
  Because disc-at-once mode writes all the data to a disc at one time, the optical disc drive writes 1 GB of dummy data to a disc even when the actual data size is less than 1 GB to ensure playback compatibility.
  Some players can play only discs that are created in disc-at-once mode. When you play the created disc on a player other than your VAIO computer, make sure if the player supports disc writing mode you selected.