Advice on ffmpeg, aac and mp4

I have some music downloads which are in the form of .m4a files and I want to cut them up using ffmpeg.

I find that something like

Quote:

ffmpeg -ss 309 -i input.m4a -to 982 -c copy output.aac

does the trick but I have the problem that I am unable to put tags on the .aac file. Easytag for instance will not write to them so I need to convert to mp4.

ffmpeg does seem to able to output directly to mp4 but I found that my software does not behave proerly with these files. What does work is going from aac to mp4.

Quote:

ffmpeg -i input.aac -c:a copy output.mp4

Now I come to the real question. The aac filesize is slightly larger than the mp4 filesize. If mp4 is a container for aac why should that be?

Is my approach correct?