Season 4 DVD Audio Commentary

Update: 8th August I've just learnt that The Beginning of The End will also feature Audio Commentary.

We've just learnt that the Episodes Ji Yeon and The Constant will feature additional Audio Commentary to go alongside the Episode on the DVD.

USA Version - DVD
USA Version - Blu-Ray
UK Version - DVD
UK Version - Blu-Ray
Canadian Version - DVD
Canadian Version - Blu-Ray

Source: DarkUFO