Editing a lossy music file

[Rincewind]

This question does not apply to a specific OS version of Audacity, nor (possibly) to Audacity alone. I'm posting in the Windows forum because it seems like they will be more 'viewers' here.

I have an .m4a (lossy) music file, created in Audacity. It is about 90 minutes long. I am interested in only the middle 20 minutes or so. How can I 'top' and 'tail' the file without losing fidelity?

If my understanding is correct, when I load the .m4a file it is converted into an Audacity Project file format. If I then truncate this file I must save it in an accepted audio file format - such as .m4a. But I am concerned that this is directly analogous to editing and saving a jpeg photo - each save operation of a lossy jpeg files causes some small, additional, loss of fidelity.

Is there no way of editing a .m4a files and saving it again such that there is no loss of fidelity?

[DVDdoug]

You are correct. Audacity (and all "regular" audio editors) decompress the audio when you load the file and if you re-export in a lossy format you are going through another generation of lossy compression.

However, MP4 (AAC) was designed to minimize the damage from multiple encodes and you should be fine. I can't find the link at the moment, but I somebody did about 100 generations and there was little or no damage (not the case with MP3!).

Or, mp3DirectCut can do limited edits on MP3 and MP4 files without decoding.

[Rincewind]

Thanks for this re-assuring confirmation.

Just out of interest are there any audio editors which can edit an MP4 (AAC) file directly, without the need for a decompression/recompression cycle?