I had to convert about 1,100 mp3 files from 44.1 kHz to 22.05 kHz so I could get them from a total of 6 gigabytes to 3 gigabytes. I just thought I would share my process.
First I had to decide what software to use. There are two that came to mind: FFmpeg and LAME. I primarily use Windows 10, but I also administer several Linux systems. I try to pick whichever one will be most efficient. For tasks I do on my own computer, I sometimes do it “natively” in Windows, and sometimes I use the Windows Subsystem for Linux, which is a full-blown Debian installation.
This time, however, I just did it in Windows. Here is the batch file I wrote to do it. I will include comments afterward. The thing to know is that the folders with the audio all have the format NN-LLL (N=number; L=letter).
First I had to decide what software to use. There are two that came to mind: FFmpeg and LAME. I primarily use Windows 10, but I also administer several Linux systems. I try to pick whichever one will be most efficient. For tasks I do on my own computer, I sometimes do it “natively” in Windows, and sometimes I use the Windows Subsystem for Linux, which is a full-blown Debian installation.
This time, however, I just did it in Windows. Here is the batch file I wrote to do it. I will include comments afterward. The thing to know is that the folders with the audio all have the format NN-LLL (N=number; L=letter).
- @echo off
- for /d %%I in (??-???) do (
- for %%J in (%%I\*.mp3) do (
- if not exist _22kHz\%%~nxJ (
- ffmpeg -i %%J -ac 1 -ab 64000 -ar 22050 _22kHz\%%~nxJ
- )
- )
- )
I put it in a numbered list so I can refer to the line numbers.
Line 3 says to get a list of all directories that have the format XX-XXX and put them in a variable called ‘I.’ I often pick ‘I’ because that's what the examples at the end of “for /?” in command prompt use, so it's a no-brainer. The ‘/d’ is necessary because the ‘for’ command will ignore directories by default.
Line 4 looks in the directory stored in variable ‘I’ and gets a list of all the mp3 files and stores them (with pathname) in the variable ‘J.’
Line 5 indicates that my output folder is called ‘_22kHz.’ I had manually created this folder (an important step!). So it says that if the file doesn't already exist in that folder, go ahead and run line 6. The ~nx is important because it basically strips the full path name of the file and gives you just the file name, so we can accurately check for it.
Line 6 is the actual FFmpeg command to convert to 64k bit rate at 22.05 kHz sampling. It reads the file in the ‘J’ variable and outputs it to the new ‘_22kHz’ folder.
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