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re-encoding an mp3 doesn't do much Sure it does, typically. It’s no different from video in this way: ideally, all of the image features that would get thrown
by celoyd 16y ago
re-encoding an mp3 doesn't do much
Sure it does, typically. It’s no different from video in this way: ideally, all of the image features that would get thrown out were thrown out the first time, but the codec isn’t that smart.
Most implementations of lossy compression algorithms don’t have stability under re-encoding as a goal. (A few do – some image editors are smart about passing through unchanged JPEG blocks, for example, and I think mp3wrap will join MP3s cleanly.)
I’m too lazy to look into exactly how he did this, but it’s not impossible that the audio artifacts came from pure MP3^n re-encoding. It’s a case that most compressors ignore.
- jerf 16y agoWhy hypothesize? Create a directory. Copy your favorite MP3 into it as both "source.mp3" and "orig.mp3". (orig.mp3 is just for convenient comparison later.) Then: for i in {1..100}; do lame source.mp3 dest.mp3; mv -f dest.mp3 source.mp3; done Then listen to the resulting "source.mp3" at the end. Send whatever params to lame you want in that command line, though the defaults strike me as pretty good for this test. BTW, when people point out that scripting this is easy, they're not kidding. We're talking shell one-liner here, forget even hitting perl. I'm on about iteration 7 as I write this and it's definitely breaking down.
- ars 16y agoSo I tried it. The biggest problem is that it gets quieter each pass. Not sure why. I tried adding --noreplaygain but it didn't help. The quality seemed to preserve OK, but as the signal get quieter and quieter the noise started becoming more obvious.
- orborde 16y agoI got silence after about 400 generations. Maybe throw a gain balancing step in there somewhere?
- celoyd 16y agoKudos for actually checking, but of course this only proves it for lame with certain flags. There are several popular compressors and many many options. As someone mentioned, YouTube doesn’t say what it uses, but it may be possible to figure it out. Learning how to do for loops in shell was a big Unix productivity breakthrough for me. I just wish the syntax were cleaner – silly things like quoting rules and not using $ on variables on the LHS keep tripping me up. I’m probably wasting my own time in the long run by not getting good with something like http://www.scsh.net/ http://www.scsh.net/ .
- deleted 16y ago[deleted]
- jokermatt999 16y agohttp://www.reddit.com/r/technology/comments/86yiq/hear_what_happens_when_you_reencode_an_mp3_600/ http://www.reddit.com/r/technology/comments/86yiq/hear_what_... A reddit post on that exact experiment. Sadly, the file is down. As a side note, I had a post here that I deleted about this, worded something like "Yes, they used that song". I went back to read the topic, and found I'd made nearly the exact same comment on the story over a year ago. I guess I'm a tad predictable. Edit: Aha! A megaupload link was posted that still works. http://www.megaupload.com/?d=ALZY0LCD http://www.megaupload.com/?d=ALZY0LCD Also related, the same experiment but for .jpg: http://www.reddit.com/r/technology/comments/86v2z/see_what_happen_when_saving_600_times_a_jpg_image/ http://www.reddit.com/r/technology/comments/86v2z/see_what_h...
- deleted 16y ago[deleted]
- ars 16y agoThat file only increased my questions on what happened to the audio on this vid. The song is quite recognizable. So why did the youtube one turn into garble? And the jpg one is just incorrect. He kept increasing the compression ratio, which proves nothing at all. For a more accurate view see http://hackerfactor.com/blog/index.php?/archives/355-How-I-Met-Your-Mother-Through-Photoshop.html http://hackerfactor.com/blog/index.php?/archives/355-How-I-M... which shows that after a certain point the jpeg stops changing. (Which is what I expected the mp3 to do, but I guess it doesn't.)
- jokermatt999 16y agoThe mp3 is probably using a different audio codec than the youtube video/mp4.