Rewrite ttml conversion

app/src/main/java/org/schabi/newpipe/download/DownloadDialog.java

@@ -832,7 +832,6 @@ private void continueSelectedDownload(@NonNull StoredFileHelper storage) {
                     psArgs = new String[]{
                             selectedStream.getFormat().getSuffix(),
                             "false",// ignore empty frames
-                            "false",// detect youtube duplicate lines
                     };
                 }
                 break;

app/src/main/java/org/schabi/newpipe/streams/SrtFromTtmlWriter.java

@@ -0,0 +1,95 @@
+package org.schabi.newpipe.streams;
+
+import org.jsoup.Jsoup;
+import org.jsoup.nodes.Document;
+import org.jsoup.nodes.Element;
+import org.jsoup.nodes.Node;
+import org.jsoup.nodes.TextNode;
+import org.jsoup.parser.Parser;
+import org.jsoup.select.Elements;
+import org.schabi.newpipe.streams.io.SharpStream;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * @author kapodamy
+ */
+public class SrtFromTtmlWriter {
+    private static final String NEW_LINE = "\r\n";
+
+    private SharpStream out;
+    private boolean ignoreEmptyFrames;
+    private final Charset charset = StandardCharsets.UTF_8;
+
+    private int frameIndex = 0;
+
+    public SrtFromTtmlWriter(SharpStream out, boolean ignoreEmptyFrames) {
+        this.out = out;
+        this.ignoreEmptyFrames = ignoreEmptyFrames;
+    }
+
+    private static String getTimestamp(Element frame, String attr) {
+        return frame
+                .attr(attr)
+                .replace('.', ',');// SRT subtitles uses comma as decimal separator
+    }
+
+    private void writeFrame(String begin, String end, StringBuilder text) throws IOException {
+        writeString(String.valueOf(frameIndex++));
+        writeString(NEW_LINE);
+        writeString(begin);
+        writeString(" --> ");
+        writeString(end);
+        writeString(NEW_LINE);
+        writeString(text.toString());
+        writeString(NEW_LINE);
+        writeString(NEW_LINE);
+    }
+
+    private void writeString(String text) throws IOException {
+        out.write(text.getBytes(charset));
+    }
+
+    public void build(SharpStream ttml) throws IOException {
+        /*
+         * TTML parser with BASIC support
+         * multiple CUE is not supported
+         * styling is not supported
+         * tag timestamps (in auto-generated subtitles) are not supported, maybe in the future
+         * also TimestampTagOption enum is not applicable
+         * Language parsing is not supported
+         */
+
+        // parse XML
+        byte[] buffer = new byte[(int) ttml.available()];
+        ttml.read(buffer);
+        Document doc = Jsoup.parse(new ByteArrayInputStream(buffer), "UTF-8", "", Parser.xmlParser());
+
+        StringBuilder text = new StringBuilder(128);
+        Elements paragraph_list = doc.select("body > div > p");
+
+        // check if has frames
+        if (paragraph_list.size() < 1) return;
+
+        for (Element paragraph : paragraph_list) {
+            text.setLength(0);
+
+            for (Node children : paragraph.childNodes()) {
+                if (children instanceof TextNode)
+                    text.append(((TextNode) children).text());
+                else if (children instanceof Element && ((Element) children).tagName().equalsIgnoreCase("br"))
+                    text.append(NEW_LINE);
+            }
+
+            if (ignoreEmptyFrames && text.length() < 1) continue;
+
+            String begin = getTimestamp(paragraph, "begin");
+            String end = getTimestamp(paragraph, "end");
+
+            writeFrame(begin, end, text);
+        }
+    }
+}