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I have a few thousand MP3 files and they are all of mixed bitrate.

I would like to run a program that can batch encode them all to 128 kbps. Are there any decent and free solutions for this for Windows?

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Any particular reason why? They'll likely sound worse than when going directly to 128 kbit/s from the CD if you re-encode them. And hard drive space is quite cheap these days –  Јοеу Jun 27 '10 at 17:10
    
My sister-in-law has about 9gb of music on the family computer and she continually screws up the machine. I then have to come over, transfer the music to a laptop, and then transfer it back after a reformat. She won't notice the difference in quality between 256 kbps and 128 kbps and the transfer time for her music collection will be almost cut in half. –  FireFly Jun 27 '10 at 17:42
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4 Answers

Simple: here's a free one: http://winff.org
Run it and add all your files then go to options button and the audio settings tab and change audio bitrate to 128.

It will take a while and bring up a command prompt where it does its magic with ffmpeg

Advanced: if you are into command lines, you can download ffmpeg and use the below command line to convert a file: ffmpeg -i source.mp3 -vn -ar 44100 -ac 2 -ab 128 -f mp3 output.mp3

If you put it into a batch file, you can convert a whole bunch at once. mine looks like this:

---convert.bat----

set formats=*.mp4 *.flv
set presets=-vn -ar 44100 -ac 2 -ab 192k -vol 400 -f mp3
set outputext=mp3

for %%g in (%formats%) do start /b /wait "" "%~dp0bin\ffmpeg.exe" -i "%~dp0%%g" %presets% "%~dp0%%~ng.%outputext%" && TITLE "Converted: "%%g

--end---
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dbPowerAmp is what I use. There is a 21 day fully functional trial, and it can handle everything in batches.

http://www.dbpoweramp.com/dmc.htm

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Dbpoweramp is such a well written program. Thanks! –  Matthew Lock Dec 6 '13 at 9:39
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My sister-in-law has about 9gb of music on the family computer and she continually screws up the machine. I then have to come over, transfer the music to a laptop, and then transfer it back after a reformat. She won't notice the difference in quality between 256 kbps and 128 kbps and the transfer time for her music collection will be almost cut in half.

I don't think the problem you have is converting mp3, but having a fast recovery process from your sister-in-law machine.

So, I suggest the following:

  • Create another partition (D: for example). C: is where you install your OS (I'm assuming it's Windows) and D: is where you keep all personal files. It's possible to move "My Documents" to another folder.
  • After formatting the machine, create a Ghost Image from your C: drive, and record a dvd with it or store on the D: partition. (You can try an OSS alternative to Ghost named Clonezilla as well)

When your sister-in-law screws up the machine, you just need to restore the Ghost Image (in 10 minutes) in your C: drive. All files in D: are kept intact.

(If you don't like my suggestion and still want to reencode the mp3s, you can use foobar2000, a free windows audio player (it can convert files too) application.)

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Converting MP3 to MP3 can cause serious audio quality problems, it is best to convert them to .wav files first, then encode them back to your desired bit rate. Regardless of what method you use, the converted files will be of lesser quality than the original MP3.

DB PowerAmp is probably the best solution to keep the directory structures intact and is great for batch work.

DB Poweramp use to be free, there may be old versions (Version 10) of it floating around on the internet somewhere, http://www.videohelp.com/tools/dBpowerAMP, you will need to download codecs and install them After DB is installed.

http://www.dbpoweramp.com/legacy/codec-central-legacy.htm

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While you're right that transcoding from .mp3 to .mp3 will reduce quality, converting back to .wav and then re-encoding to .mp3 isn't going to help anything. In fact, almost every transcoder already does exactly this behind the scenes. –  afrazier Jun 28 '10 at 1:08
    
Not the ones I have used like DB or CDEX, I can hear the difference using both methods, at least that has been my observation. –  Moab Jun 28 '10 at 13:02
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