I have numerous m4a files bought from Itunes and When I edit the date in the ID tag which apple has as 2009:29837272287 And I change it to just 2009

it will change my kbps from 256 to sometimes 258 or sometimes 252, why is that?



P.s. Not sure if m4a is considered AAC so I apologize if this is in wrong area.

You're in the right area. Songs from iTMS store that are encoded with the iTunes Plus setting are actually encoded with a variable bit rate setting. Play a song with foobar and you'll see they are not 256kbps constant.

Well winamp displays a song to be 256 kbps the whole time but if i edit the date tag it will change the kbps which will stay constant the whole time

Download and play it in foobar. The bitrate that is displayed in Winamp's main window will just round the bitrate to either 128, 192, 224, 256, 320, etc. So 252 & 258 will still be 256.

but why is changing the date changing that number, is a frame being removed or added or something?

try changing the year guys from an itunes store purchase