I"m on the process of removing the ADTS header from a raw aac+ frame and put it inside an m4a container. The issue come when the container needs a fixed or variable flag set for the raw aac+ frame sizes.

How could I modify this frames to be fixed sized without loosing or breaking any audio quality? I'm doing this programatically...

According to ISO standard for MPEG-4 max raw aac frame size is 2^13

Help?
Thanks!