Converting MP3 to WAV formats
In last lab we will learned how to play an audio file stored on the flash memory or SD card. We used an early version of a Python module that plays .WAV files in a fixed format: 8,000 samples per second using 16-bit encoding. Because there are hundreds of different formats of audio files, we need a consistent way to convert all of these formats to 8K samples/second 16-bit .WAV formats.
The audio data file conversions are done on your host PC, not the microcontroller. This allows us to use a rich library of tools that don't need to run on our microcontroller.
Method 1: Use the ffmpeg Command Line Tool
One of the easiest ways to get started is to go to the web site ffmpeg.org and download the program that does the conversion using a command line. Note that on a Mac you will need to go into your System Preferences and indicate that the following programs are trusted:
Here are the direct links for MacOS
This will download a zip file which you will need to unzip and place in a location such as
~/bin. After you do this make sure you add
`~/bin to your path by adding the following file to your .bash_profile:
After you source your .bash_profile type in the following:
This should return the location that it finds the ffmpeg shell script. You can then see the many file-format MPEG options:
Converting MP3 to 8K 16 bit WAV Files
To get the format we need for the MicroPython wave player class we just specific
-i for the input file and use the
-ar 8000 to specify the output bit rate of 8K samples per second. The final parameter is a file name that must in
.wav so the command knows to use WAV PCM encoding. The default value is 16 gits per sample.
We can use unix shell commands to do a batch conversion of all the . The following is an example of using awk and sed to convert all the .mp3 files in a directory and convert them to 8K Hz WAV files and put them in a sibling directory.
Inspect the Files Using the UNIX file command:
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Note that these are WAVE audio, Pulse-code Modulated (PCM), 16 bit and mono at 8K Hz.
Method 2: Use the pydub Python Module
This section is only for experienced Python developers.
Install Conda and the Python libraries
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Check your versions:
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Transferring the Files with Rshell
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