Option to set output quality to original quality

This is not a bug. Re-compressing a lossy file always results in generation loss, especially recompressing a low quality file with poor quality would result in horrible quality. See http://en.wikipedia.org/wiki/Generation_loss#Techniques_that_cause_generation_loss_in_digital_systems

Stefan, I think Carlos want something like "80% of the quality of the original file", so you can assign a target bitrate for each file, based on the original one.
That's not so easy to do, it's not a feature I can manage to add at the moment (how do you handle lossless->lossy?, etc...).
But all patches and ideas are welcomed :)

It depends.
If you by quality mean the actual sound quality, then 80% pretty much means "low" quality (or some other constant setting) in the current interface.

But if you mean bitrate (as soundconverter currently does) I don't think this would be a useful setting for 3 reasons.

1) Let's say I want to convert a 192kb/s AAC and a 96kb/s vorbis to mp3. So I convert them to 154kb/s and 77kb/s respectively. The former still is probably quite close to CD quality while the second is by far less than "very low quality".

2) Generation loss highly depends on the techniques used in both the compression and the re-compression.

3) It would not be accessible to the user what 80% means in that context and especially the higher settings like "120% of original quality" would need a lot of explanation. So even if this is hypothetically useful to some, it would be confusing for most users to see that option.