I talked a bit with my fellowlodger about several topics concerning mp3s & frames and we got stuck at the question if there is a program out there which can replace frames below a specified volume level (e.g. - 50.0 dB) with absolutely silent frames. I can't remember of a tool with this ability.

The starting point of our discussion was a 320 kbit CBR encoded radio drama which has a lot of short pauses. If these pauses (in this case all encoded with 320 kbit) would be replaced with '32 kbit silence' the whole filesize would be formidably reduced. This requires a threshold for the silence detection (every frame with volume level below the given value will be treated as silence) like mp3DirectCut's silence detection.
After that process the file will be VBR instead of CBR - a very unusual mp3, it only has 320 kbit and 32 kbit frames - so the file has to be scanned to determine the average bitrate which will be written in the new header.

After all we reduced the filesize of the mp3s (mp3s at any bitrate, CBR, ABR, VBR) without reencoding.

What's your opinion or statement?

Doing that is probably going to be a mess. I doubt anyone has written something to resize existing frames, but I don't see why you couldn't.

Wouldn't it be easier to do that when encoding instead using the already existing features of LAME. For example --abr 320 --athlower -30

Thank you for your replies.

@Mike Giacomelli:
Of course this method has to be used with care and in moderation and should only be applied to the right files (for instance those radio dramas) - music files will become mutilated (disfigured?).
As this method is still powerfull it has to be difficult of access (for instance click on the pic in about dialog to open a new dialog where this option can be enabled).
The threshold has to be low enough to preserve the lingering (or 'die away') of the last letter of any word (~echo) or quiet music playing in the background - any mistake will kill to much informations.

@ErikS:
I have never used such options relating ATH-curve but this is a possibility I didn't think of.
I also never have searched for the right commandline for radio dramas as I am only listining to it - for my music files --aps is the best way.
I don't want to reencode those files since there is no need for it (enough disk space, satisfying quality, no sharing of mutilated mp3s).

In my opinion such an option (replace silence - or quiet parts - unnecessarily encoded with high bitrate - with low bitrate) is quiet fine.

I will write a mail to Martin Pesch - maybe he like such a feature too and feel like spend some time with it.