I would like to convert a large collection of WAV files to AAC using the "iTunes Plus" setting in iTunes. iTunes describes this setting as:
128 kbps (mono) / 256 kbps (stereo), 44.100 kHz, VBR, optimized for MMX/SSE2.
I would like to automate this import process.
Trial and error
afconvert command line tool can convert between audio file formats. I've tried a few settings and the closest I could get is:
afconvert -v -d aac -b 256000 -f m4af -q 127 -s 2 --soundcheck-generate input.wav output.m4a
So: be verbose (
-v), use the AAC data format (
-d aac), encode at 256 kbps (
-b 256000), store in the Apple MPEG-4 Audio file format (
-f m4af), use the highest quality (
-q 127), use VBR constrained (
-s 2) and add SoundCheck data to the file.
I've also created an
m4a file using the iTunes Plus setting.
m4a file created by
afconvert is about the same size as the iTunes file; just 65536 bytes smaller.
afinfo tool, I compared the file generated by iTunes to the file generated by
afconvert. There are two differences in the
- The file generated by iTunes has an
audio data file offsetof 131072, the one by
afconvert65536. This explains the difference in file size
Somehow the file generated by iTunes has different
sound checkvalues than the one converted by
sc ave perceived power coeff 343 407 sc max perceived power coeff 6873 8940 sc peak amplitude msec 154389 194861 sc max perceived power msec 194025 194025 sc peak amplitude 31129 30928
sc ave perceived power coeff 341 388 sc max perceived power coeff 6087 4157 sc peak amplitude msec 212509 152323 sc max perceived power msec 215481 185017 sc peak amplitude 31024 29857
sc peak amplitude msecand
sc max perceived power msecvalues differ quite a lot. These are the exact same input files, what could cause this difference?
Is there a way to get results even closer to the "iTunes Plus" setting?