However, torrents would be a lot smaller, and easier to share, if the pirates just ripped directly into multichannel AAC.

After all, you can now decode AC3 into multichannel AAC (via Handbrake). That’s all they’d need to do! AAC provides much better compression so by using AAC, torrents would be faster and easier to rip, upload, and download…and it would be easier to store more of them on your computer because they take up less space!

For instance, here’s what Dolby.com has to say about AAC:

AAC (Advanced Audio Coding) is a perceptual coding method used to compress digital audio files for efficient storage and transmission. Upon playback, the expanded files can provide sound quality nearly indistinguishable from the original sources. In principle, AAC is similar to MP3, but offers a number of advantages designed to improve audio quality. These include higher-efficiency compression, more channels, and better handling of audio frequencies above 16 kHz. The improved efficiency of AAC files makes AAC a particularly good choice for streaming audio over the Internet.
AAC, developed in part by Dolby Laboratories, is one of several audio coding systems defined by ISO MPEG standards, where it was first specified as MPEG-2 AAC, and then enhanced and extended within MPEG-4. Apple’s popular iTunes® music service employs the AAC format.

“Why wouldn’t Amazon/Walmart/etc. have standardized on AAC as well?”

Because companies are too lazy to do something different, and would rather play on the ignorance of their customer base.

When Amazon announced their store I called them in this, for what it’s worth:

http://thesmallwave.com/2007/05/21/amazon-to-sell-drm-free-music-online-in-the-wrong-format/

Indeed, you are correct. I ripped “Human” from the Killers at 256 kbps CBR in both AAC and MP3. The MP3 file is 7.5 MB. The AAC file is 5.7 MB. That’s a very significant difference.

What’s odd about AAC is that Apple are the only company to really jump on the format, despite its obvious advantages (and the length of time it’s been on the market now). Why wouldn’t Amazon/Walmart/etc. have standardized on AAC as well?

It appears the naming choice (Advanced Audio Coding (AAC)) was a tremendous marketing blunder by the founders.

“…The confusion over whether AAC is an “Apple format” is in some measure a byproduct of the format’s acronym, and that many people assume that one of the A’s in “AAC” stands for “Apple”. (It stands for “Advanced Audio Coding”.) If it were called, say, “MP4” instead, it might be more clear that it’s the successor to MP3.”

Well worth the read.

http://daringfireball.net/2007/04/some_facts_about_aac

“isn’t the bitrate the literal amount of data contained in a file?”

Not at all. Feel free to rip the same song at 256K MP3 and 256K AAC and you’ll see different files sizes. AAC files are smaller at the same sample rate (and sound better).

I think the argument should be that AAC sounds as good as MP3 at a *lower bitrate*, making for a smaller file size. But since we’re assumedly comparing iTunes Plus (256 kbps) AAC to Amazon MP3 (256 kbps), the file sizes should be similar if not identical. But the iTunes Plus song should sound *better*.