In Order to unlock all video and audio files you will need to not only complete all specialists training but also complete 13 Challenges,
You can see your challenge progress simply by pressing the options button when in the Specialist HQ
You can complete all challenges while getting all the stars for the Centennial Trophy
The Challenges are as Follows:
- Earn 10 Bronze Stars (Complete 10 skirmishes on Recruit)
- Get 15 consecutive kills in 1 round without dying
- Get 10 kills with each of the primary weapon classes
- Get 25 melee kills
- Get 50 kills with secondary weapons
- Earn 10 Silver Stars (Complete 10 skirmishes on Regular)
- Get 100 Headshot Kills
- Get 50 Kills using the Score-streaks
- Get top of the scoreboard 25 times
- Get 100 Kills using Specialist Weapons and Equipment
- Get 150 Kills on Veteran
- Earn 10 Gold Stars (Complete 10 Skirmishes on veteran)
- Complete all Combat Immersion Challenges
These Challenges should all come as you are attempting to get the gold stars on each of the specialists skirmishes :D but if you don't you can always go back and replay and skirmish to finish them off
Hopefully this helps you out :D