Damaged mp3s
July 13, 2007 8:57 AM   Subscribe

Why do mp3s get damaged?

Over the course of years, going back to pre-Napster (1st generation) days and ripping a very large collection of CDs, I have amassed a fairly large mp3 library. I currently use ITunes on a Mac but, in my PC days, I used other software, including MusicMatch, foobar and I-Tunes. At various times, I have noticed that files have somehow got damaged. This has been noticed, e.g. on an individual basis or when (re-)uploading the whole collection to the music-playing software or when checking the files, e.g. with IVolume as suggested the other day on AskMeFi (http://ask.metafilter.com/33334/iTunes-Sound-Levels-for-Burning-a-CD). When I last checked (which I did about a year ago by playing every file in my player) everything seemed OK or was fixed. IVolume, however, has spotted various errors, including No Tags (though tags seem to show), which is easy to fix, QT error (which needs fixing, e.g. with DBPowerAmp or re-ripping) and Silent (which needs re-ripping). My question is a) how do those files get damaged (I have not had any crashes or other disasters) and b) why do IVolume and DBPowerAmp show errors though ITunes does not, i.e. tags are shown, the file plays perfectly?
posted by TheRaven to Computers & Internet (6 answers total) 1 user marked this as a favorite
With modern operating systems, files rarely become damaged without a hint that the actual hard drive is damaged. I think you are seeing different programs handle error conditions differently and handle different tag versions inconistently.
posted by mzurer at 9:04 AM on July 13, 2007

There were a lot of buggy encoders out around the year 2000. Xing and BladeEnc particularly were problematic. Of course at the time all the players had to support whatever crap you threw at them (I know because I worked on Sonique). I think in the last five years the number of encoders has shrunk, and the ones out there have become much higher quality. I definitely have some mp3s that windows media player won't play, but foobar2000 will.

So even without the possibility of filesystem corruption, you could have a bunch of mp3s that were never very good, but some players accept.
posted by aubilenon at 9:17 AM on July 13, 2007

I've certainly thought I'd noticed this phenomenon, but aubilenon's explanation could certainly fit my situation. Also I think some CD drives I've used have introduced errors into the resulting MP3s whereas others never do.
posted by dance at 10:30 AM on July 13, 2007

have you tried a stripped-down and free of BS mediaplayer like Media Player Classic?
posted by jimmyhutch at 10:47 AM on July 13, 2007

Media Player Classic uses the same codec that the big awful version uses.

But if you have access to a PC, try foobar2000 or winamp or something to at least see if the files are just sketchy.

You might be able to decode them and then reencode them, but that will cause quality loss. Probably no matter what the cause of the problem you're stuck with reencoding them.
posted by aubilenon at 12:06 PM on July 13, 2007

"including No Tags (though tags seem to show)"

iTunes is probably using some sort of internal database to store the metadata and not writing back to ID3v1/ID3v2 tags.

Also, foobar2000 used to like writing MP3 tags as ID3v1+APEv2 by default, which some players may interpret as damage.

Other errors may be indicative of a hardware problem; for example, most memory in desktop systems etc isn't ECC protected, so is vulnerable to being flipped by cosmic rays or manufacturing defects.

Another fairly common problem is network corruption; TCP uses checksums to keep the probability of errors low, but some network chipsets (especially modern GigE ones) support checksum offloading; basically, performing checksum generation and verification in hardware so the CPU doesn't need to bother. Sadly it's quite common for manfuacturers to get it wrong, leading to potential data corruption; this goes for other offload technologies too, like Large Send Offload and TCP Segmentation Offload, but they're somewhat less common.

Hard disks and optical drives have fairly extensive error correction systems, but again it's probabilistic, and won't catch absolutely everything, especially with failing or marginal media. Some disk controllers are also somewhat notorious for munging data before it even hits a disk, and may be the cause for more widespread undetected corruption.

Probably more likely, as aubilenon said, is you simply have marginally broken MP3's produced by buggy encoders like Xing, and probably been through broken systems, buggy P2P software, and so forth. Less forgiving codecs are likely to have problems with them.

Second the foobar2000 recommendation; it's got a "Rebuild MP3 Stream" option which may be of use, and if you've got any old APEv2 tags, you can have it migrate them to the rather more compatible ID3v2 format.
posted by Freaky at 12:16 PM on July 13, 2007

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