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m4a files from iTunes

Mar 22, 2016 at 10:16 PM
m4a files from iTunes return IsVBR=false, while MediaInfo (SourceForge) shows that they are in fact VBR.

Other evidence also suggests the m4a files I am testing are VBR:
1) ATL and MediaInfo both show non-standard bitrates.
2) I understand that the default iTunes profile is to download in VBR format.
Mar 30, 2016 at 5:33 AM
Alright. I'll look into it in the next days.

M4A specification clearly mention VBR-specific parameters that ATL needs to recognize better.

Thanks for pointing this, dowdybrown
Mar 30, 2016 at 10:59 PM
Edited Mar 30, 2016 at 11:01 PM
That's done !

Contrary to what I thought, VBR detection on M4A files is especially tricky, and relies on analyzing individual sample sizes variations to "infer" the use of variable bitrate.

As of MediaInfo behaviour, ATL now considers "VBR" any M4A audio whose sample size variation is over 1%.

M4A sample and test case has been included in the project for VBR detection.
I have yet to find a CBR M4A on my hard drive...


Out of curiosity, what kind of project are you using ATL for ?
Marked as answer by Zeugma440 on 2/13/2017 at 7:50 AM