VBR/CBR File Size

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Level 1

70 points

VBR/CBR File Size

I am running into a perplexing issue regarding file sizes of VBR vs CBR encoding...

I have a my entire library of songs ripped from CDs that were encoded at AAC 256Kbs 44.1KHz. In the name of saving space (and after doing some reading), I re-ripped a few CDs using the same encoding settings, only selecting the VBR 256Kbs instead of strait 256Kbs (AAC of course). Now, I was expecting some slightly smaller files sizes, but what I found were files significantly larger than they were in the first place. Some gained 2MBs or more, depending on the length of the song. A possible variable in this, however, is that some of the songs in questions were ripped years ago...I'm guessing 2003 time frame using iTunes 4.x. Is it possible that with the years of iTunes updates that new/improved encoding techniques would result in larger files? Or am I wrong in my understanding that VBR files are "potentially" smaller than their CBR counterparts?

Thanks
G

15" Powerbook G4 1.25, Mac OS X (10.5.7), iPhone 3G w/ OS 3.0

Posted on Jul 27, 2009 6:30 PM

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Answer 1

Chris CA

Level 10

82,513 points

Jul 27, 2009 6:37 PM in response to ggarthe

When using VBR, the rate slected is the minimum rate.
Passages with more data will use a higher bitrate, so songs will be larger than CBR encoded songs.

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Answer 2

ed2345

Level 9

63,602 points

Jul 27, 2009 6:58 PM in response to ggarthe

+"Or am I wrong in my understanding that VBR files are "potentially" smaller than their CBR counterparts?"+

The argument you heard was probably more like "a smaller VBR file can have equivalent audio quality to a larger CBR file." This is because, as Chris notes, they spend more bits on the more sonically complex passages, and less on the sonically simple passages.

If you want to experiment, you can compare 192 w/ VBR (it's a custom setting) versus 256 w/ CBR. But, if you are shooting for a particular file size to save space, CBR will be more predictable.

Message was edited by: ed2345

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Answer 3

Chris CA

Level 10

82,513 points

Jul 28, 2009 8:28 AM in response to ed2345

they spend more bits on the more sonically complex passages, and less on the sonically simple passages.

My (little) understanding is the only time it actually goes less than the selected bitrate is if there is little/no audio for more than an extended period (more than x seconds).

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Answer 4

ed2345

Level 9

63,602 points

Jul 28, 2009 3:25 PM in response to Chris CA

Chris, That is correct. I meant "less" in the relative sense, not to mean "less than the nominal value."

Some players, such as Winamp, display the instantaneous bitrate during playback, so on a VBR file you can see it vary as the song plays. Sometimes it will change a couple of times a second.

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Answer 5

ggarthe Author

Level 1

70 points

Jul 30, 2009 4:34 PM in response to ggarthe

Well, I did some experimenting and you guys have it right. I tried a song with areas of little to no sonic activity (Pink Floyd's Shine On You Crazy Diamond), and the VBR file was smaller than CBR version, all other setting being equal. Other songs that are active from beginning to end were larger with VBR. At any rate, I guess I'll just stick with CBR. I was hoping VBR would save me some space, but I'll find other ways to trim corners cuz it won't be with my music.

Thanks guys!

G

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