AAC codec builds upon state-of-the art signal processing technology from Dolby Laboratories and brings true variable bit rate (VBR) audio encoding to QuickTime.The encoding settings in iTunes doesn't list VBR options.
Now if all AAC encoding rates are VBR (are they?) what do the bitrates mean? Guaranteed minimums? Rough middle ground? Never quite understood previous iTunes mp3 VBR settings either. Unlike LAME encoding which made much more sense (and was documented). Anyone have any ideas about the mp4 settings?
Maybe you should test it yourself with two different WAVs/AIFFs that you know are completely opposite in sound and resulting bitrates. If you get almost the same file size afterwards, QT 6 uses CBR.
Another test for this whole VBR question. I just recorded 5:32 of silence to a wav/aiff, burned to a CD-RW, then encoded to 224 kps mp4. Byte count is 9,382,203, nearly identical to both earlier tracks.
well, that's not true, i guess..try it and you'll find that this happens during the whole file.
i'm actually very convinced!but, i meant files, which i encoded on my own with iTunes 4.2.proof it yourself.
This is iTunes 188.8.131.52. No "VBR" in the classic sense here.