AC3 Dolby and AC3 2.0

[PuzZLeR]

I'm running HandBrake in Windows, but Mac users can help I'm sure. In the Audio Track menu I sometimes get two sources.

What is the difference between?
1 English (AC3) (Dolby)
and
2 English (AC3) (2.0)

I can't understand the difference, and why there's two tracks, and why only one episode may have this on the entire disc when the rest just have the "(Dolby)" option. If it was a choice between 2/6 channels fine, but this? I did read the HandBrake guide (well done, thanks!), and do understand Dolby, but what is this multiple thing?

Question 2:

This has been asked but the answers aren't satisfying to be honest. I too want to "future proof" my stuff.

Let's say the DvD source has a Dolby 5.1 AC3 track. An obvious choice is the AAC 6 channel option. Right?

Lets' say though you don't have the decoders for AAC 5.1, but are confident they will be much more abundant in the future, will AAC 5.1 be fully backward compatible to 2 channels with a 2 channel decoder in the meantime?

Thanks so much for reading.

[realityking]

Question 1:
The 2-Channels Track has only 2 two tracks (duh), Dolby could mean anything. ProLogic (4 Channels, matrix encoded), Prologic 2 (5 Channels, matrix encoded) or real surround sound with up to 7 Channels (however the maximum HandBrake can preserve are 6 Channels). Dolby is definitively better then stereo, just how much better isn't clear from what you give us

Question 2:
No 6-Channels AAC aren't backward compatible. (Perfect example: iPod), however at least ?TV and QuickTime are able to perform a downmix to stereo.

[PuzZLeR]

Thanks for your answers.

Just to give you an idea, the track labeled “English (AC3) (2.0)” is really a voice-over narration where the directors/producers do a discussion over the one chosen episode of the disc, which is what I should have clarified earlier. That’s why one episode has two tracks and others don’t.

Nobody’s really sure what the difference between “(AC3) (2.0)” and “(AC3 (Dolby)” really is technically, but I’m assuming they’re both two channels, and feel safe encoding them using the AAC Dolby Pro Logic II option.

Of course my iPod version will be only encoded to “Stereo”.

[hawkman]

Looks like you may have a couple of misconceptions here.

You don't need a stereo track in order to have stereo output. Obviously, encoding to more channels than are in your source material is pointless as you can't add information that's not there. However, encoding to fewer channels is not a problem at all. Handbrake happily downmixes the channels, so it can make your 5.1 audio into 2.0 stereo. No need to worry.

Not only that, but Dolby Pro Logic II is actually a stereo track. That means your iPod will play it fine. It's got some clever engineering that means if you play it back through a compatible encoder - such as in your DVD's surround sound system - you'll get surround sound (though not as good as with discrete 5.1). However, if you play it though a "dumb" device, it won't see anything but a stereo track.

[PuzZLeR]

It's clear now, thank you folks.

Yes, encoding to a 6 channel output from a 2 channel source is obviously unnecessary.

As far as I'm concerned, with this thread's info, and as the HB guide says, to be safe I will stick with Dolby Pro Logic II for everything except if the source if definitely 5.1. Then I can obviously go with AAC 6 Channel Discrete.

Makes sense to me now. Thanks!