Java - Downsampling from 22050 to 8000 gives zero bytes

Question

I'm trying to downsample a .wav audio from 22050 to 8000 using AudioInputStream but the conversion returns me 0 data bytes. Here is the code:

AudioInputStream ais;
AudioInputStream eightKhzInputStream = null;
ais = AudioSystem.getAudioInputStream(file);
if (ais.getFormat().getSampleRate() == 22050f) {
    AudioFileFormat sourceFileFormat = AudioSystem.getAudioFileFormat(file);
    AudioFileFormat.Type targetFileType = sourceFileFormat.getType();
    AudioFormat sourceFormat = ais.getFormat();
    AudioFormat targetFormat = new AudioFormat(
        sourceFormat.getEncoding(),
        8000f,
        sourceFormat.getSampleSizeInBits(),
        sourceFormat.getChannels(),
        sourceFormat.getFrameSize(),
        8000f,
        sourceFormat.isBigEndian());
    eightKhzInputStream = AudioSystem.getAudioInputStream(targetFormat, ais);
    int nWrittenBytes = 0;
    nWrittenBytes = AudioSystem.write(eightKhzInputStream, targetFileType, file);

I already checked AudioSystem.isConversionSupported(targetFormat, sourceFormat) and it returns true. Any idea?

Answer 1

I have just tested your code with different audio files and everything seems to work just fine. I can only guess, that you are either testing your code with an empty audio file (bytes == 0) or, that the file you try to convert is not supported by the Java Audio System.

Try using another input file and/or convert your input file to a compatible file, and it should work.

Here is the main method, that worked for me:

public static void main(String[] args) throws InterruptedException, UnsupportedAudioFileException, IOException {
    File file = ...;
    File output = ...;

    AudioInputStream ais;
    AudioInputStream eightKhzInputStream = null;
    ais = AudioSystem.getAudioInputStream(file);
    AudioFormat sourceFormat = ais.getFormat();
    if (ais.getFormat().getSampleRate() == 22050f) {
        AudioFileFormat sourceFileFormat = AudioSystem.getAudioFileFormat(file);
        AudioFileFormat.Type targetFileType = sourceFileFormat.getType();

        AudioFormat targetFormat = new AudioFormat(
                sourceFormat.getEncoding(),
                8000f,
                sourceFormat.getSampleSizeInBits(),
                sourceFormat.getChannels(),
                sourceFormat.getFrameSize(),
                8000f,
                sourceFormat.isBigEndian());
        if (!AudioSystem.isFileTypeSupported(targetFileType) || ! AudioSystem.isConversionSupported(targetFormat, sourceFormat)) {
              throw new IllegalStateException("Conversion not supported!");
        }
        eightKhzInputStream = AudioSystem.getAudioInputStream(targetFormat, ais);
        int nWrittenBytes = 0;

        nWrittenBytes = AudioSystem.write(eightKhzInputStream, targetFileType, output);
        System.out.println("nWrittenBytes: " + nWrittenBytes);
    }
}