Fixes a bug in the getMatching method causing the input list to lose all matching elements

src/main/java/net/knarcraft/ffmpegconverter/converter/AudioConverter.java

@@ -13,19 +13,19 @@ import java.util.List;
  * A converter for converting audio files
  */
 public class AudioConverter extends AbstractConverter {
-    private final String newExt;
+    private final String newExtension;
 
     /**
      * Instantiates a new audio converter
      *
      * @param ffprobePath <p>Path/command to ffprobe.</p>
      * @param ffmpegPath  <p>Path/command to ffmpeg.</p>
-     * @param newExt      <p>The extension of the new file.</p>
+     * @param newExtension      <p>The extension of the new file.</p>
      */
-    public AudioConverter(String ffprobePath, String ffmpegPath, String newExt) {
+    public AudioConverter(String ffprobePath, String ffmpegPath, String newExtension) {
         this.ffprobePath = ffprobePath;
         this.ffmpegPath = ffmpegPath;
-        this.newExt = newExt;
+        this.newExtension = newExtension;
     }
 
     /**
@@ -76,6 +76,6 @@ public class AudioConverter extends AbstractConverter {
 
     @Override
     public void convert(File file) throws IOException {
-        processFile(file.getParentFile(), file, newExt);
+        processFile(file.getParentFile(), file, newExtension);
     }
 }

src/main/java/net/knarcraft/ffmpegconverter/utility/ListUtil.java

@@ -40,6 +40,7 @@ public final class ListUtil {
      * @return <p>A new list containing all matching elements.</p>
      */
     static <T> List<T> getMatching(List<T> list, Predicate<T> predicate) {
+        list = new ArrayList<>(list);
         List<T> copy = new ArrayList<>(list);
         list.removeIf(predicate);
         copy.removeAll(list);