Improves converters to remove some code duplication

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

@@ -1,7 +1,10 @@
 package net.knarcraft.ffmpegconverter.converter;
 
+import net.knarcraft.ffmpegconverter.streams.StreamObject;
+
 import java.io.File;
 import java.io.IOException;
+import java.util.List;
 
 /**
  * This interface describes a file converter
@@ -15,4 +18,15 @@ public interface Converter {
      * @throws IOException <p>If the file cannot be converted.</p>
      */
     void convert(File file) throws IOException;
+
+    /**
+     * Generates a command for a ProcessBuilder.
+     *
+     * @param executable <p>The executable file for ffmpeg.</p>
+     * @param file       <p>The input file.</p>
+     * @param streams    <p>A list of ffprobe streams.</p>
+     * @param outFile    <p>The output file.</p>
+     * @return <p>A list of commands</p>
+     */
+    String[] builderCommand(String executable, File file, List<StreamObject> streams, String outFile);
 }