handbrake dvd ripping audio ac3/aac compatibility question

the default behavior in handbrake is to put 2 audio tracks in my mp4 dvd rip

track 1 is a stereo mixdown of the DVD audio (often a mixdown from 5.1 to stereo) in AAC format

track 2 is a passthrough of the audio (no transcode) in ac3 format

my question is:

why bother with both of these tracks? which devices potentially lack the capability to play 5.1 ac3 audio? Is it just iOS devices? If I play back in iTunes or other media software, will it play the lossless track by default? I'm considering dropping the stereo mixdown (track 1) to save some time and space while doing the encode.

 

I think this explains the reasoning.

https://trac.handbrake.fr/wiki/SurroundSoundGuide

 

perfect. +rep.

 

Also, you can actually check which soundtrack you want to play in a video file (so long as you are using the m4v extension and container, it is a little different from the standard mpeg-4 container and mp4 file name) right within iTunes. I believe it will play the surround sound option by default but you can always select which one you want. I also think that the iPad and iPad 2 can output 5.1 surround sound through the new HDMI adapter (Apple is calling it the Digital AV Accessory) that was released alongside the iPad 2. The 4G iPod touch and iPhone 4 may also have the same abilities as they too work with the HDMI adapter and are running the same hardware as the iPad (though the A4 is debatably running at a slower speed). I am not sure about those two devices though as I have only heard success stories with the iPad and iPad 2.

So, unless you have an iPod or iPhone, there really is no reason to keep using the downmixed transcoded AAC audio option alongside the passthrough 5.1 AC3 soundtrack.

 

I do have an iPhone, it only adds about 70 MB / hour to the movie size to include it - I just want to make sure that track doesn't play (hopefully by default it will play the better track) on devices that can handle it.

In iTunes, I see the button to change audio tracks, and the surround option is greyed out. Granted, this is on my laptop running on the internal speakers. Maybe if I send the audio through the mini DP, it will let me do surround?

 

Id assume for those who play it with a xbox 360 and other limited front end devices.

You can always remux the final file without the extra audio track to save some size or use a different encoder all together (MeGUI)

 

That is something I haven't tried out yet. I have a 3rd party mini displayport to HDMI adapter but I have yet to hook it up to my TV to playback video content with AC3 5.1 Dolby Digital audio. It might work, I will have to look into that later today after I get back from work.

Right now, I wouldn't do anything with the down mixed 2.0 track simply because you have an iPhone. As you said, it only an extra 70MB and that really isn't a whole lot in the grand scheme of things especially when you are already looking at 700+ MB videos.

 

by the way - is this a decent way to handle audio consistently? I'm trying to keep the file sizes relatively small. Basically, for compatibility, I'm sort of following the surround sound guide:

- audio track 1 is a pro logic II encode
- audio track 2 is ac3 (6 channel)

is it ok if I don't pick ac3 passthrough for the second track? What's the difference between specifying 6 channel discrete and the passthrough? Shouldn't that be the same? Also- does it matter if I pick the same source for the both? Specifically- if a 5.1 AC3 track already exists, I might want to do AC3 passthrough on track 2 from the AC3 source and do the pro logic 2 on track 1 from the lossless audio source. However, the implication in the handbrake guide seems to imply that the audio source must be the same for both tracks, but that doesn't make any sense to me.

To keep things consistent, can I just always select the lossless audio source and specify a pro logic 2 encode on track 1 and an ac3 6 channel encode on track 2?

Can someone help me swim through all of this?

 

Passthrough means that the audio is simply passed through to the resulting m4v file. It isn't transcoded or modified in any way, shape, or form. The audio in the final m4v file will be exactly the same as the source (likely a DVD). My main area of confusion comes from your ability to select a lossless source. I have some music video DVDs with 2.0 PCM WAV audio but that is about it. I have yet to come across a commercial DVD release with lossless audio (which would be 2.0 PCM WAV as a dual-layer DVD isn't enough to house lossless surround sound for an entire movie).

Theoretically going with the lossless audio would provide you the best results simply because the audio engineer behind the release has already mastered it down to two channels for you. Also, you would be working with a lossless source when encoding down to AAC. AC3 (Dolby Digital) is lossy. So, when you encode that down using AAC, you are going through a lossy-to-lossy transcode and it is generally frowned upon in the audio community. Whether or not you will actually hear the difference all depends on your blind listening test results.

So I would just go with passthrough for your second audio track as that is exactly what you want. You don't want Handbrake re-encoding another multi-channel AC3 audio track (lossy-to-lossy transcoding) or altering the original in any way. Just have it "copy and paste" the surround sound to the resulting movie. Then, for the first audio track, I suggest selecting the lossless audio source (which won't always be there) and encoding it to 2.0 AAC for iPhone compatibility.

I would be happy to show you my exact Handbrake encoding settings that I use to produce good results. I still haven't tried outputting 5.1 Dolby Digital audio from my MBP using the mini display port either. I was too busy yesterday but I can try it out tomorrow.

 

the lossless source would be from blu ray only. DVDs usually just have the AC3 audio track.

I'm going for good compression and high compatibility here, and I don't want handbrake to run into any issues. One thing that concerned me was that the surround sound guide made it seem like if you do 2 tracks the audio source must be the same.

So yeah, basically for DVD sources I'm convinced that I should be doing an AAC pro logic 2 mix on track one and a passthrough of the AC3 5.1 on track 2.

I don't know what the best option is for blu ray sources though. They often contain lossless 5.1 audio tracks. I've basically been using that track to generate the AAC pro logic 2 mix and the 5.1 AC3 mix at 448 kbps. I'm wondering what my best option is for track 2 (lossless is huge and not an option, but I want something of moderately high quality)

 

OK, I didn't realize you were ripping Blu-ray movies as well. You don't have much of a choice for the second option when it comes to ripping Blu-ray movies as you simply cannot go lossless with the passthrough option. You would have to transcode to 5.1 AC3. I wouldn't worry about the quality though since that should have roughly the same quality as commercially produced DVDs. Also, unless you have conducted a volume matched blind ABX test between a handful of 448kbps 5.1 AC3 tracks and the source lossless tracks and were able to distinguish between the two, I don't think you have much to worry about (this is something that the majority of people would fail).

So going with 2.0 AAC for one audio track and 5.1 AC3 448kbps for the second track is about your only option for encoding Blu-ray movies as going with anything higher would void iTunes, iPhone, iPad, AppleTV, etc. compatibility. Personally, I don't think it is essential either and would definitely be overkill. Your choices are pretty limited as to what Handbrake can do and I think you are taking the best route.

Edit: Alright, I just checked. Dolby Digital 5.1 output works on my 2011 13" MBP using a 3rd party mini displayport to HDMI adapter. I had a few m4v files (some downloaded from the iTunes Store, I encoded others) with 2.0 AAC audio and 5.1 AC3 (I think the bitrate for the AC3 audio for each video was at 448kbps). My receiver successfully registered that Dolby Digital 5.1 audio was being sent to it.

 

yeah, i was just worried that maybe handbrake had some sort of weird limitation that I was missing based on the surround sound guide.