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Converting videos - better to mixdown 5.1 or 2.0 audio track?

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bwh79

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I'm using HandBrake to convert some of my DVD movies to import into iTunes and play on my Apple TV and iPod Touch. I don't (currently) have a 5.1-channel speaker setup (but nothing says that can't change in the future.) I've heard that 5.1 audio doesn't sound very good when played through standard Stereo equipment. (That is, I've heard people say that, I haven't heard it with my own ears...) Some DVDs only have a 2.0 audio track, and some only have 5.1, but sometimes they have both. When both are available, would I be better off using the 2.0 or 5.1 track? Or maybe use the 5.1 for the AC3 passthru and 2.0 for the AAC mixdown (ATV2 preset makes 2 audio tracks, one a straight passthru of the AC3 audio direct from the DVD, and the other an AAC mixdown [to Dolby ProLogic II -- also should I leave that as is, or go down to plain old Stereo?] for devices that don't support AC3 passthru)?

I don't know much about the subject, just enough to know that I don't really know what I'm doing, so if you could give me any reasoning behind your answers, or links to any guides on the subject, it'd be appreciated.
 
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Sparkee

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If you choose the Apple/Universal or an ATV preset in Handbrake it should automatically create both a 5.1 and a stereo mix down if the 5.1 is available on the DVD. Both audio tracks are present in the video file and the appropriate track is selected automatically when played by the device. When you play the movie on the ATV connected to a home theater the 5.1 track is used. If you transfer it to an ipod touch and play it the stereo track is selected. The 5.1 audio can be disabled on the ATV's Settings if it is not properly detected when preferring the stereo track.
 

bwh79

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If you choose the Apple/Universal or an ATV preset in Handbrake it should automatically create both a 5.1 and a stereo mix down if the 5.1 is available on the DVD.
[Pre-Edit: Wow, I got a little long-winded there. It's amazing how many words it can take to nail down an idea that's just like *that* in your mind. Here's the TL>DR version -- is it best to just always use the 5.1 source track from the DVD when it's available, or am I better off selecting the 2.0 source when I'm mixing down to 2.0 output file and/or playback equipment?]

Thanks, but maybe I wasn't totally clear in my question. Handbrake does make two tracks on the Apple TV preset -- one is just a straight passthrough of the source track with no compression (AC3 Passthru) and the other (AAC Mixdown) is compressed to AAC and converted to Dolby ProLogic II (by default, though you can select other mixdowns like Stereo, Mono, or Dolby Surround.) My question is about which track from the DVD to use as a source for these two tracks in the output file, particularly the mixdown.

Several of the DVDs I've come across so far have only either 2.0 or 5.1 audio, so with those ones there's no question. However, a few of them have both tracks available (as well as additional tracks for other languages, director's commentary, etc., but I'm not concerned with those), and for each track in the final output file, you can individually select which source it comes from. I don't think Handbrake has any sort of default behavior as far as preferring 5.1 or anything when it comes to selecting a source, it just chooses whichever one is labeled "Track 1," and uses that as the default source for both of the output tracks.

So one track that Handbrake makes is the AC3 Passthru. This is a bit-for-bit reproduction of the audio stream from the DVD. I understand that it (Apple TV) won't play this track unless it's connected to a home theater system. Does it have to be a 5.1 system? Is there even such a thing as a home theater system that's not 5.1? I don't imagine there would be much sense in using the DVD's 2.0 track as a source for this whenever there's a 5.1 track available. I might as well use the 5.1 here and then I'll have it available if and when I get a better setup.

Or do I have that wrong, and it will only play through a home theater if it's an actual 5.1 track, but otherwise would play the AC3 Passthru track just fine through my TV set if it comes from a 2.0 source? If that's the case I could use the 2.0 track and it would play the uncompressed audio through my TV insetad of the AAC mixdown. What kind of difference would you expect in quality, then, between this 2.0 passthru and the compressed AAC?

The other track that Handbrake makes is the AAC Mixdown. This is for playback on devices that don't support the AC3 Passthru, like my TV set, or basically anything else I have (VLC will play the 5.1 tracks on my computer, but it's only got a pair of desktop speakers attached...) This is what I'm mostly wondering about, because it applies to the movies I'll be watching on my TV right now, instead of movies I might be watching on some possible home theater system in the future.

I've heard that 5.1 audio doesn't sound good (something about levels, and maybe being out of phase?, etc. I'm not up on all the technical details of it), when played back through 2.0 equipment. Now, I'm guessing this means like if I put the movie in my DVD player and chose the 5.1 track, and played it just through my TV speakers. That wouldn't sound good, and I'd be better off using the 2.0 mix. But it can't sound too bad, though, because many (ok, some. A few? At least one of my) DVDs only have a 5.1 track, and you don't even get to select a 2.0 if you wanted it.

So, how does this apply to mixing down the audio? I can select the 5.1 track, and mix it down to Dolby ProLogic II. This I understand is a way of encoding surround sound info into just two channels of audio. Then, when you play it back on suitable equipment, it decodes the signal into its component parts and plays them back in surround sound. But this I don't quite understand -- I mean it makes sense if you're working in a medium that only has two channels available like a VHS or a cassette tape, but in a digital file it doesn't make much sense to me -- if you've got the surround sound home theater setup, wouldn't you just use the AC3 Passthru track anyway? And if you don't have the surround sound setup, does that encoding leave any artifacts that get in the way when playing back through 2.0 equipment? Is that what people are talking about when they say it doesn't sound good? Would I be better off using the 2.0 source track, and just choosing the "Stereo" mixdown in handbrake?

Basically, I want to know which of these is best to use for playback on my TV set:

5.1 -> Dolby ProLogic II
2.0 -> Dolby ProLogic II (would this just be the same as 2.0 -> Stereo?)
2.0 -> Stereo
(there's also 5.1 -> Stereo, but that doesn't seem like it'd be good for anything.)
 
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Sparkee

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For the most part I think you are complicating thing more than you need to. The default presets in Handbrake do a pretty good job at keeping things simple for the user (I'm all about keeping things simple these days). Sure there may be better options, but you'll probably need to be the 1% of the population with "golden ears" to hear the difference, especially on low end audio conversion (I would consider even the best TV's on board audio to be low end and I do not have golden ears).

I am no expert here but I would guess using the 5.1 option mixed down to Prologic as well as adding the 5.1 for the future to be a good option. Prologic is basically a stereo track that will sound good on a stereo TV which most have fairly poor speaker systems anyways. A Prologic track should allow any multi speakers receiver to simulate a reasonably good surrond sound out of the sound track no matter how many speakers they have. The way most devices work these days, if the ATV detects it is connected to a 5.1 receiver it will choose that track activating all the speakers. A 7.1 receiver will typically take the 5.1 track and mix the rear surround channels into the 2 additional rear channels it has.

Most good home theater receivers will detect the source audio and automatically decode the audio in the best way it can for the amount of speakers it has. My guess is anything above stereo should include a prologic mix along with the ac3 passthrough (5.1). Mixing 2.0 to prologic would be over kill and should be left to stereo. Leave that conversion to the receiver which will probably mix it up to prologic, good home theater receivers are designed well to make this conversion and sound good. Basically I recommend staying with the options the Handbrake presets choose which in my experience already do what I explained, if it makes sense.
 
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bwh79

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Ok so it looks like you are saying I should stick with the 5.1 source track whenever that's available, and only fallback to the 2.0 track when there is no 5.1? And in that case, go ahead and mixdown to stereo, not the default ProLogic?
 

Sparkee

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Like I stated above, for the most part sticking with the presets already in Handbrake will give you the best results. Namely the Universal or ATV presets. Always add the 5.1 track or AC3 pass through for the future when you may add a surround sound system to your set up. Handbrake will take the 5.1 and mix it down to a prologic mix which is great for stereo or other receivers that can not handle the full AC3 stream. If all there is is a stereo track there is no additional information for it to create a prologic track so Handbrake will automatically set the output to stereo. There is no need for you to choose anything different. I have not tried the ATV presets which I would imagine will work on any reset touch or iPhone. I always use the Universal preset which does perfect fine choosing the right audio options automatically creating movie files with the 5.1 passthrough which plays great on my home theater as well as the prologic mix which plays fine in stereo on my touch and iPhone.

A lot of smart people already put the time in to creating the presets in Handbrake which already automatically choose the best options. Trying to create you own presets will cost you a lot of time and experimentation and probably only give you a tiny, if any, improvement over the presets already there.
 

bwh79

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So, in a nutshell:

-Use the 5.1 source from the DVD for all output tracks when it's available. (This was really all I wanted to know)

-Don't change the preset settings. (I never really meant to, except as noted below)

-When there is no 5.1 and the DVD only has 2.0, it's not necessary to change "ProLogic II" in the mixdown settings to "Stereo" because the output will be the same? (This was my secondary concern. I'm pretty sure it doesn't actually change automatically to Stereo when you select a 2.0 source, it still says ProLogic in the settings. On the other hand, if you're converting a video file with AAC audio and your preset is set for MP3 passthru, for example, it will select a different conversion option. If you run a 2.0 Stereo track through ProLogic, do you end up with a plain 2.0 Stereo track, or does it somehow attempt to "upmix" or "ProLogic-ify" the track in some way?)

...correct?
 
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