Editing lossy files

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Editing lossy files

2014-10-20 23:12:06

I've discovered a very annoying artifact in an iTunes purchase and I'm wondering about the best way to get rid of it. I was thinking of converting the file to a waveform, editing it, and then reencoding it back into AAC.

As it's the same codec being applied to the file twice (assuming the iTunes store uses the same encoder they include in the iTunes software), will this subject my file to further lossiness?

Editing lossy files

Reply #1 – 2014-10-20 23:19:30

Quote from: UnderFalseFlags on 2014-10-20 23:12:06

As it's the same codec being applied to the file twice (assuming the iTunes store uses the same encoder they include in the iTunes software), will this subject my file to further lossiness?

Yes.

Editing lossy files

Reply #2 – 2014-10-20 23:24:58

There will be theoretical quality loss, but it might not be noticeable and it may be preferable to the artifact you are now hearing.

AAC was designed for minimal "damage" from re-encoding, and it's not as bad as MP3 in this regard.

I'm not sure if using a different encoder will make a difference.

I'm not sure what quality setting is used for the iTunes store, but if your re-compressed file ends-up significantly smaller than the original, try a higher quality setting to minimize the amount of data that's thrown-away. And if file size is of no concern, it wouldn't hurt to use the highest quality setting for re-encoding.

The general advice is always to avoid re-compressing lossy files, but sometimes we don't have a choice.

Editing lossy files

Reply #3 – 2014-10-20 23:38:11

http://www.squared5.com/svideo/mpeg-streamclip-win.html apparently allows cutting of iTunes (mp4/m4a) audio without re-encoding. I'm not 100% sure about that. Might be worth a try. Requires QuickTime or an old QT Alternative.

Editing lossy files

Reply #4 – 2014-10-21 06:30:35

Despite the name, mp3DirectCut (http://mpesch3.de1.cc/mp3dc.html) is supposed to be able to edit AAC files without re-encoding. I used to use it for cutting MP3 files a few years ago and it always worked well. I just gave mp3DirectCut a go with a few AAC files (which I hadn't tried before) and had very little success as it kept crashing (NB: you have the rename the file extension to *.aac in order to open them). You might have more success than I did, so it's an option at least.

Editing lossy files

Reply #5 – 2014-10-21 10:49:09

I heard a small artefact in an iTunes purchase once. I highlighted it to Apple who refunded the purchase within days (though I could keep the file) and alerted the record label of the issue. I should probably delete the original file and purchase it again to see if it was fixed by the record label in the mean time but it was such a minor issue that I haven't bothered to do that yet.

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