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Topic: Apple Lossless 5.1 (Read 10799 times) previous topic - next topic
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Apple Lossless 5.1

Hey there guys. I have been searching the net high and low and i am findling it difficult to get a clear cut answer to my question so i figured asking you guys will most likely point me in the right direction.

I have 5.1 WAV's that i wish to play on my ipod/itunes. ALAC is my chosen lossless format as it is fully compatible with itunes/ipod and i can plug it straight into my car stereo. I wish to play to files in itunes and also keep them on my ipod. I normally use dbpoweramp but the ALAC codec doesnt support it and Mediacoder doesn't have an ALAC option. I have also tried AIFF, this almost worked as i was able to import them to itunes and on my ipod but there was no playback.

So, my question is... can ALAC handle 5.1 audio and is there a program that will convert these files? If not, is there a lossless format that is playable on itunes/ipod and will support 5.1?

Cheers guys.

Apple Lossless 5.1

Reply #1
You can do multichannel aiff (not sure about wav) but not multichannel ALAC.  You can import a high resolution aiff/wav and convert to ALAC within iTunes, but if you import a multichannel aiff, if will error out when it starts the conversion.

Apple Lossless 5.1

Reply #2
So, my question is... can ALAC handle 5.1 audio and is there a program that will convert these files?

It's possible to have more than two channels in ALAC. You can use XLD (on OS X) to convert between various lossless formats. But, is the iPod essentially a stereo playback device? How will it handle 5.1? A downmix?

- Kewl

Apple Lossless 5.1

Reply #3
I'm pretty sure XLD doesn't actually generate multichannel ALAC files.  Last time I tested it, XLD would indicate multiple channels in the stream info atom, but only 2 channels were present in the stream itself.  It was a definite  moment when I found that out.

While the ALAC frame headers support up to 8 channels in the stream, there's no defined way on how to handle anything above 2.  And it's a moot point so long as iTunes and iPods don't handle multichannel audio at all.

Apple Lossless 5.1

Reply #4
Quicktime is able to load 6-channel WAV file and export it to .MOV file with ALAC compressed audio.

Don't know how to demux alac from mov and mux it into standard mp4 container.

Apple Lossless 5.1

Reply #5
I'm pretty sure XLD doesn't actually generate multichannel ALAC files.

I'm pretty sure it does. I tried it before I wrote my initial post and I just tried it again.

- Kewl

Apple Lossless 5.1

Reply #6
ALAC will support up to 8 channels. You can use afconvert to encode and convert.

CAF, on the other hand, is said to support one thousand (possibly more) channels. Has anyone been crazy enough to actually attempt to confirm this, I wonder?

Apple Lossless 5.1

Reply #7
CAF, on the other hand, is said to support one thousand (possibly more) channels. Has anyone been crazy enough to actually attempt to confirm this, I wonder?
I'm not *that* crazy, but I've tested CAF up to 64 ch. with BoomRecorder. Works fine, but be prepared for large files

Apple Lossless 5.1

Reply #8
I see XLD's been updated in the past few months and it's handling of multichannel is very interesting.  It's punting ALAC encoding to CoreAudio by looking at its source code, so that's not very helpful.  But from dumping its mdat atom output I can see that it's actually using multiple 1-2 channel ALAC frames, concatenated and without any byte alignment or trailing footer between them to represent a single set of multichannel samples.  For instance, it turns a single 6 channel block into frame1(1ch)->frame2(2ch)->frame3(2ch)->frame4(1ch)->footer->align - similar to how WavPack's blocks work.  Since the channel count field is 3 bits and the footer is also 3 bits, it serves as a sort of "stop" indicator depending on whether its value is 0, 1, or 7 (all set).

Now I'm going to have to update my ALAC decoder and encoder to handle these

Apple Lossless 5.1

Reply #9
Umm... What is actually the point in having files with more than two channels on your iPhone / iPod? Neither the headphone output nor the dock connector support multichannel playback.

Apple Lossless 5.1

Reply #10
Umm... What is actually the point in having files with more than two channels on your iPhone / iPod? Neither the headphone output nor the dock connector support multichannel playback.


Not having to convert songs to have the same files on your computer/Ipod/media center/etc...
That's probably the reason to have lossless at all on a portable player.

Apple Lossless 5.1

Reply #11
Even then I don't really see a purpose.  Storage is so inexpensive these days that most people can afford an additional internal/external hard drive.  They can always expand the storage capabilities of their notebooks/desktops.  However, on a portable device such as an iPod, it really doesn't make sense to carry around a 5.1 lossless file as the size will be huge.  You can't expand the storage capacity of an iPod so it would make more sense to have two different versions of the same file: a 5.1 version for home playback and a 2.0 version for the iPod.  There are far more negatives to carrying around a 5.1 lossless file on a portable device when compared to the positives.  Then again, I am also a firm believer that lossless is not needed on a portable device in general.

 
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