Trim opus without FFMPEG in JAVA

OpusFileUtil.java

// I had partial success, the file plays but in media players the duration will be shown of original audio and the position jumping to trimmed section

// with dependency on https://github.com/leonfancy/oggus

// See issue: https://github.com/leonfancy/oggus/issues/2


import org.chenliang.oggus.ogg.OggPage;
import org.chenliang.oggus.ogg.OggStream;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class OpusFileUtil {


    static long sampleRate = 48;
    static long streamPreskip = -1;
    static long streamGranulePosFirst;

    public static void trim(long fromMs, long toMs, InputStream source, File result) throws IOException {
        OggPage prevPage = null;

        Log.oneLine("OGGPAGETRIM START ======================");

        OutputStream outputStream = new FileOutputStream(result);

        OggStream oggStream = OggStream.from(source);


        outputStream.write(oggStream.readPage().dump()); //1st id page
        outputStream.write(oggStream.readPage().dump()); //2nd comment page
        outputStream.flush();

        while (true) {
            OggPage oggPage = oggStream.readPage();
            if (oggPage == null) break;
            long pageMsStart = prevPage == null ? 0 : getPageMsEnd(prevPage);
            long pageMsEnd = getPageMsEnd(oggPage);
            Log.oneLine("OGGPAGETRIM MS_START " + pageMsStart + "OGGPAGETRIM MS_END " + pageMsEnd);

            if(pageMsStart > toMs){
                break;
            }
            if (pageMsStart >= fromMs && pageMsEnd < toMs) {
                Log.oneLine("OGGPAGETRIM " + oggPage.getGranulePosition() + " IN RANGE --------------------");
                outputStream.write(oggPage.dump());
                outputStream.flush();
            }

            if (prevPage == null) {
                //this is first page
                streamGranulePosFirst = oggPage.getGranulePosition();
            }
            prevPage = oggPage;
        }



    }

    static long getPageMsEnd(OggPage page) {
        return (page.getGranulePosition() - streamGranulePosFirst - streamPreskip) / sampleRate;
    }
}