Adds new converters

Adds a MKV to HEVC converter which aims to reduce file-sizes
Adds a MKV to MP4 transcoder which allows selection of each type of stream

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

@@ -41,7 +41,7 @@ public class WebVideoConverter extends AbstractConverter {
 
         //Get first streams from the file
         SubtitleStream subtitleStream = getNthSubtitleStream(streams, 0);
-        VideoStream videoStream = getFirstVideoStream(streams);
+        VideoStream videoStream = getNthVideoStream(streams, 0);
         AudioStream audioStream = getNthAudioSteam(streams, 0);
 
         //Add streams to output