“I noticed in iTunes Movie, those HD video on sale or rent carries Dolby Digital 5.1 audio track. I thought iPad only play AAC? Does that mean these HD videos available in iTunes Store can't be play on iPad or iPad in fact can play Dolby Digital 5.1 audio track?”
The M4V video from iTunes contains multiple audio tracks. Not only does the video have an AC3 track, but also an AAC stereo track. When you play back iTunes movies and TV shows on your iPad, it will use the AAC stereo track instead of the AC3 track.
Can iPad play the AC3 track in iTunes movies and TV shows? Yes and No. Check the new iPad/iPad 2 specifications and you’ll find that the new iPad and iPad 2 actually support “Dolby Digital 5.1 surround sound pass-through with Apple Digital AV Adapter”. The word pass-through means your iPad delivers Dolby Digital 5.1 audio to an AV receiver/amplifier that decodes AC3 rather than decodes the audio on its own. Since iPad does not have an HDMI out port, you need to use an AV Adapter to connect iPad with HDMI.
How to have new iPad play HD movies with Dolby Digital 5.1 audio?
Basically, here is what you need:
1. Your new iPad/iPad 2
2. Apple Digital A/V adapter (buy one from Apple Store)
3. An HDMI cable
4. An AV receiver that supports AC3 decoding.
And to watch iPad video on HDTV, you’ll need a 2nd HDMI cable to connect AV receiver with HDTV.
[Step-by-step Guide] iPad Connection for Dolby Digital Pass-through
1. Plug the Digital A/V adapter in to your iPad 2. Make sure the adapter is seated well.
2. Plug the HDMI cable into the smaller of the two slots of the adapter.
3. Next, insert the plug on the other end of the HDMI cable into an open HDMI port on your AV receiver/amplifier.
4. If you’d like to mirror iPad screen to your HDTV, connect AV receiver with HDTV using another HDMI cable.
5. Now press play on your iPad’s Videos app, you’ll get HD video and Dolby Digital 5.1-channel surround sound through a single cable.
If the HDTV does not show iPad screen, check if you have switched the input on your HDTV to the right HDMI connection port. Use your dock-to-USB cable and USB power adapter to keep your iPad charged while connected if necessary.
iPad to play MP4 with Dolby Digital 5.1 sound?
Nowadays lots of movie fans rip their DVD and Blu-ray movies to MP4 video in HD 720p/1080p with Dolby Digital 5.1 sound. Such kind of video may play well with VLC media player and various other media center app (XBMC, PLEX, Tiversity, etc), but it is not compatible with iPad. The iTunes simply would not accept MP4 video with AC3 – seems confusing but it is true – it only lets you add M4V videos with both AC3 and AAC audio track, or with AAC stereo exclusively. This rule also applies to Apple TV. And you can find the following passages from an Apple support page on encoding video for Apple TV :
“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
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.”
If you want to keep original AC3 audio and still enjoy the movies on iPad and Apple TV, convert your videos to M4V and ensure there’re both AAC stereo and AC3 5.1 audio track included. Learn more details at Convert Blu-ray for streaming to ATV 3 with Dolby Digital 5.1 pass-through .