Apple TV will pass through 5.1 surround sound audio encoded in Dolby Digital AC-3. The AC-3 audio must be properly included in the movie in order for it to pass through correctly.
To create content for use with Apple TV, the movie must have two audio tracks:
- Advanced Audio Coding (AAC) stereo
- AC-3 track for surround
Note: Both tracks should have the same sample rate (48 kHz is normal).
For compatibility, the following is required:
- Both tracks must be provided.
- The AAC track should be first and it must be enabled.
- The AC-3 track should appear after the AAC track and it should be disabled by default.
- The AC-3 track must also use the appropriate MPEG-4/ISO standard.
Apple TV uses the AC-3 track as a pass-through mode only. For example, it passes data out to an A/V receiver capable of Dolby Digital playback. The AC-3 audio is sent over the HDMI and the optical audio output of Apple TV.
To select AC-3 data through these ports, go to Settings > Audio > Dolby Digital Out and select On.
These movies can be created using applications such as FinalCut Express and FinalCut Pro.
Note: The AAC track is used in any situation where just stereo output is required.