5.1 Sound on Apple TV - Thoughts Scratchpad

[EvilRob]

But if so, why would there be reports of 'cut and paste' AC3 audio tracks into a .mov container working?

Because a Quicktime MOV container and an MPEG-4 container are not the same thing. There are strict rules on what the public streams in an MPEG-4 container must contain.

The Quicktime MOV container has no such rules, and permits you to jam all manner of crazy data into it, including an AC3 audio track.

 

[BobVB]

Because a Quicktime MOV container and an MPEG-4 container are not the same thing. There are strict rules on what the public streams in an MPEG-4 container must contain.

The Quicktime MOV container has no such rules, and permits you to jam all manner of crazy data into it, including an AC3 audio track.

You misunderstood my question: if the mp4 container method was required, why would the .movs be working....

But we now know from the demo VisualHub .mov file that an AC3 stream will work. Either the Handbrake .mkv AC3 settings are inherently incompatible or Perian does something when it saves the movie as a .mov tom make the AC3 track unavailable to AppleTV.

 

[gopher]

Still it Handbrake is able to add AC3 audio tracks from a movie DVD that has had them encoded to an M4V file which AppleTV will then recognize and output as 5.1 sound. I've tested and proven this myself.

 

[BobVB]

Still it Handbrake is able to add AC3 audio tracks from a movie DVD that has had them encoded to an M4V file which AppleTV will then recognize and output as 5.1 sound. I've tested and proven this myself.

well my copy of Handbrake 0.9.1 won't let me do that and I don't have one as old as 0.7.1. Mine only allows Dolby Prologic II in MP4 files and the AC3 passthru of .MKV files aren't recognized by iTunes.

 

[EvilRob]

You misunderstood my question: if the mp4 container method was required, why would the .movs be working...

They're not mutually exclusive. There are three different things we know work:

1. Quicktime MOV containers with appropriately named and prepared AC3 audio streams work. We know this because there are working samples, including the VisualHub sample file.
2. Quicktime MOV containers with with a losslessly encoded AC3 PCM stream work. We know this because it's worked since AppleTV 1.0.
   
3. MPEG-4 containers with an appropriately named and prepared AC3 audio stream work. We know this because this is the format that the Apple movies with AC3 use. Incidentally, the Apple movies store the AC3 track in a private stream, and put a normal stereo track into the audio stream, thus making a legal MPEG-4 file.

Does that answer your question?

 

[BobVB]

They're not mutually exclusive. There are three different things we know work:

1. Quicktime MOV containers with appropriately named and prepared AC3 audio streams work. We know this because there are working samples, including the VisualHub sample file.
2. Quicktime MOV containers with with a losslessly encoded AC3 PCM stream work. We know this because it's worked since AppleTV 1.0.
   
3. MPEG-4 containers with an appropriately named and prepared AC3 audio stream work. We know this because this is the format that the Apple movies with AC3 use. Incidentally, the Apple movies store the AC3 track in a private stream, and put a normal stereo track into the audio stream, thus making a legal MPEG-4 file.

Does that answer your question?

Actually if you read my note you realize I no longer had any of those questions. My only one now is how to get an AppleTV playable file out of Handbrake.

 

[gopher]

Looks like downgrading Handbrake may be the only option unless you can get these settings out of the newer versions. As I saw a newer version of Handbrake came out, my encoded files were not encoded as well, were choppier, or Handbrake unexpectedly quit in the middle of encoding.
These settings I used with my version of Handbrake:

Average Bitrate 1800 kbps
Sample rate 48000 Hz
Bitrate 128 kbps
File Format MP4
Codec AVC/H.264 Video/AAC Audio
Audio Language AC3, or Dolby II/Digital

 

[BobVB]

Looks like downgrading Handbrake may be the only option unless you can get these settings out of the newer versions. As I saw a newer version of Handbrake came out, my encoded files were not encoded as well, were choppier, or Handbrake unexpectedly quit in the middle of encoding.

Well I found a copy of Handbrake 0.7.1 and I found the settings are only about the source. It gives you no choice of the output which is 2 channel AAC for the MP4 selection.

Open one of the files you created in Quicktime Player and use the Movie Inspector - you will see that the sound is just a 2 channel AAC track.

 

[csimon2]

But if so, why would there be reports of 'cut and paste' AC3 audio tracks into a .mov container working?

Dunno. Did this work with the 1.x version of aTV sw? I don't have an aTV so I am really just speculating off of what I know to work in most other environments where H264 and AC-3 have to be married into a single file. I thought I had read though that people reported that this method wasn't working. But if this has been enabled from the beginning, then I don't know why more people weren't targetting this method. I know I would have been at least.

Either the Handbrake .mkv AC3 settings are inherently incompatible or Perian does something when it saves the movie as a .mov to make the AC3 track unavailable to AppleTV.

Most likely answer is that with the default version aTV sw, mkv isn't recognized properly. And when you are saving as a .mov directly to from a .mkv, there is either some header information in the way or not present that aTV expects. Have you ever tried the following?:

1. Use MKVExtract to extract the H264 to a .264 and the AC-3 to a .ac3 elementary stream
2. Use YAMB to mux the .h264 to a .mp4
3. Open the h264 .mp4 and ac-3 .ac3 in QT and then copy and paste those two tracks into a newly saved .mov file

They're not mutually exclusive... There are three different things we know work:

Thanks for the roundup. So, I had some followup questions, in respective order to your list. (This aTV update and price drop has finally got me to consider getting one.):

1. I assume that this is going to work with the default version of the aTV sw? No hacking required?
2. What sw was used that was capable of doing this before? Just curious...
3. So it sounds like what Apple is officially doing for their rentals is .mp4 with stereo aac and private ac3. Correct?

 

[EvilRob]

Thanks for the roundup. So, I had some followup questions, in respective order to your list. (This aTV update and price drop has finally got me to consider getting one.):

I assume that this is going to work with the default version of the aTV sw? No hacking required?

Yes, this works with the default software. I'm willing to hack my own AppleTV, but I want something that works for friends and family as well.

What sw was used that was capable of doing this before? Just curious...

The only one that worked prior to AppleTV 2.0 was number 2 from my list, the losslessly encoded AC3 track. There was no easy software to do that, you had to extract the AC3 track and encode it yourself, then mux it back into the file to be played. It was ugly. ;-)

So it sounds like what Apple is officially doing for their rentals is .mp4 with stereo aac and private ac3. Correct?

Yes, that's correct. There may be more than just stereo in the AAC soundtrack (ie. ProLogic II), but that's what is inside the MPEG-4 containers from Apple. If you want a close look at one without the DRM baggage from a rental, the new AppleTV intro movie is also in this format and can be extracted from the update image, which can be downloaded with some hackery.

 

[BobVB]

That was quick

There is a patch in the HB source that allows for the creation of mp4 with AC-3 passthru. Did a test compile and it does work.

This does NOT create a file like the HD rentals that have a Pro Logic II and a DD5.1 audio track which could possibly come in the future.

 

[dynaflash]

... which could possibly come in the future.

very possibly

 

[Cave Man]

very possibly

dyna, you're such a tease.

 

[dynaflash]