AAC music files are “lossless” yet fairly compact - very useful for those who want the highest fidelity yet small sized music files.
Unfortunately, exporting such files is a one-at-a-time manual process, because there is currently no “Export as AAC” in the macro list of commands.
Please add this file type in the “Manage Macros… Insert…Choose Command” list, thereby enabling batch processing exports for multiple music files with this format.
Thank you for considering this Audacity enhancement. I suspect this improvement is going to be highly valued by Audiology users, but likely will require relatively little effort to complete.
AAC is a “lossy” format, though there is a related format called ALAC (Apple Lossless Audio Codec) which is “lossless”.
(If you have a “lossless AAC” file, then it is probably an MP4 container with ALAC encoded audio)
If you want a lossless compressed format that is supported natively by Audacity, use FLAC.
I think you are greatly underestimating the difficulty of adding this feature.
AAC support in Audacity is provided by FFmpeg, which supports a huge number of options (many, but not all of the options are available via Custom FFmpeg Export Options. ALAC is not currently supported by Audacitys FFmpeg implementation.
I agree that it would be nice for Audacity to have more flexible options for exporting via macros / scripting, but I don’t think that the case for “lossless AAC” is stronger than, for example, Opus, WMA, AAC (lossy), AC3, APE, or many other audio formats. A possible solution might be to provide a scripting command for “Export with external encoder”, taking command line arguments to use any codec that the user has installed on their machine.