More than 10 years ago, disappearing 'cdec' tags, written by Nero AAC Encoder, seem to have been a problem.
Here the link:
Just recently, when checking some Nero encoded files, I had to realize that the problem came back. The moment you press the save button in MP3tag, the cdec tag is gone.
Now, it seems that thousands of files are affected in my collection, as I recently updated most of the tags. Apart from the cdec tag, there is no way to ever retrieve the information again, which parameters have been used for encoding.
Of course there are backups - suffering from the lost tag, too. It's usually a piece of information in encoded files you don't worry about much. Only recently a situation came up that required to know the compression mode and rate, when duplicates of recordings occurred. Since different versions of the encoder (which is still possible to see in the files) have different output files, you cannot judge by the file size.
At present, it is difficult to tell how many files are affected, as the collection is part of a resource for an Internet radio station. And the cdec is one of the tags that most normal tag apps don't put on the screen.
Florian wrote that the tag was gone for quite a while and I cannot remember when I stopped using version 2.92. I am usually quite conservative with updating apps if newly added features don't really affect me.
The thing is that modifying tags is something you do possibly many times after the encoding of the original, which can be a very long time ago in the past...
Anyway, thanks to Florian for fixing again this old issue with mp3tag.
The information is available in v3.24b via an undocumented information field %_cdec% so you could use this with the Filter to identify files with the missing fields that need to be restored from backup.
Thanks for the immediate upate/fix of the problem, Florian. As previously mentioned to 'MotleyG', backups cannot be used as they also suffer from lost tags, considering that the cdec bug returned to the software some ten years ago. The backups, usually done annually, shall mainly reduce the risk of loss due to hardware failures, not software failures. Once an audio track is encoded, you assume the tag app won't touch that information, and modifications to tags are done relatively often. I would say that almost every file has undergone tag modifications within the last ten years.
Nevertheless, the audio part of files is not affected, it's only the loss of the individual compression parameters, which is bad news for the maintenance.
Also thanks for the hint about the filter but as I said, most backups will have lost the information, too. And checking some 40,000 AAC-encoded files would make some automatic processing necessary anyway.
Nevertheless, keep up the good work, Florian! And please make sure that, in the future, mp3tag will not touch any unknown/unidentified tags.
You could do this the other way around. Filter your current library for the files missing the %_cdec% tag. Then use the backup library to populate that tag back to the current files that have the other more recent tag edits.
Make sure you keep a true backup separate in this case, in case, you know...