Grub frames preview from youtube

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeStreamExtractor.java

@@ -1035,4 +1035,29 @@ public class YoutubeStreamExtractor extends StreamExtractor {
             }
         };
     }
+
+    @Nullable
+    public StreamFrames getFrames() {
+        try {
+            final String script = doc.select("#player-api").first().siblingElements().select("script").html();
+            int p = script.indexOf("ytplayer.config");
+            if (p == -1) {
+                return null;
+            }
+            p = script.indexOf('{', p);
+            int e = script.indexOf("ytplayer.load", p);
+            if (e == -1) {
+                return null;
+            }
+            JsonObject jo = JsonParser.object().from(script.substring(p, e - 1));
+            final String resp = jo.getObject("args").getString("player_response");
+            jo = JsonParser.object().from(resp);
+            final String[] spec = jo.getObject("storyboards").getObject("playerStoryboardSpecRenderer").getString("spec").split("\\|");
+            final String url = spec[0];
+            final List<String> opts = Arrays.asList(spec).subList(1, spec.length);
+            return new StreamFrames(url, opts);
+        } catch (Exception e) {
+            return null;
+        }
+    }
 }

extractor/src/main/java/org/schabi/newpipe/extractor/stream/StreamFrames.java

@@ -0,0 +1,113 @@
+package org.schabi.newpipe.extractor.stream;
+
+import javax.annotation.Nullable;
+import java.util.ArrayList;
+import java.util.List;
+
+public class StreamFrames {
+
+	private final List<Frameset> frames;
+
+	public StreamFrames(String baseUrl, List<String> params) {
+		frames = new ArrayList<>(params.size());
+		for (int i = 0; i < params.size(); i++) {
+			String param = params.get(i);
+			final String[] parts = param.split("#");
+			frames.add(new Frameset(
+					baseUrl.replace("$L", String.valueOf(i)).replace("$N", parts[6]) + "&sigh=" + parts[7],
+					Integer.parseInt(parts[0]),
+					Integer.parseInt(parts[1]),
+					Integer.parseInt(parts[2]),
+					Integer.parseInt(parts[3]),
+					Integer.parseInt(parts[4])
+			));
+		}
+	}
+
+	public int getVariantsCount() {
+		return frames.size();
+	}
+
+	public Frameset getVariant(int index) {
+		return frames.get(index);
+	}
+
+	@Nullable
+	public Frameset getDefaultVariant() {
+		for (final Frameset f : frames) {
+			if (f.getUrl().contains("default.jpg")) {
+				return f;
+			}
+		}
+		return null;
+	}
+
+	public static class Frameset {
+
+		private String url;
+		private int frameWidth;
+		private int frameHeight;
+		private int totalCount;
+		private int framesPerPageX;
+		private int framesPerPageY;
+
+		private Frameset(String url, int frameWidth, int frameHeight, int totalCount, int framesPerPageX, int framesPerPageY) {
+			this.url = url;
+			this.totalCount = totalCount;
+			this.frameWidth = frameWidth;
+			this.frameHeight = frameHeight;
+			this.framesPerPageX = framesPerPageX;
+			this.framesPerPageY = framesPerPageY;
+		}
+
+		public String getUrl() {
+			return url;
+		}
+
+		public String getUrl(int page) {
+			return url.replace("$M", String.valueOf(page));
+		}
+
+		public int getTotalPages() {
+			if (!url.contains("$M")) {
+				return 0;
+			}
+			return (int) Math.ceil(totalCount / (double) (framesPerPageX * framesPerPageY));
+		}
+
+		/**
+		 * @return total count of frames
+		 */
+		public int getTotalCount() {
+			return totalCount;
+		}
+
+		/**
+		 * @return maximum frames count by x
+		 */
+		public int getFramesPerPageX() {
+			return framesPerPageX;
+		}
+
+		/**
+		 * @return maximum frames count by y
+		 */
+		public int getFramesPerPageY() {
+			return framesPerPageY;
+		}
+
+		/**
+		 * @return width of a one frame, in pixels
+		 */
+		public int getFrameWidth() {
+			return frameWidth;
+		}
+
+		/**
+		 * @return height of a one frame, in pixels
+		 */
+		public int getFrameHeight() {
+			return frameHeight;
+		}
+	}
+}

extractor/src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeStreamExtractorDefaultTest.java

@@ -231,4 +231,29 @@ public class YoutubeStreamExtractorDefaultTest {
             assertFalse(extractor.getDescription().contains("https://youtu.be/U-9tUEOFKNU?list=PL7..."));
         }
     }
+
+    public static class FramesTest {
+        private static YoutubeStreamExtractor extractor;
+
+        @BeforeClass
+        public static void setUp() throws Exception {
+            NewPipe.init(Downloader.getInstance(), new Localization("GB", "en"));
+            extractor = (YoutubeStreamExtractor) YouTube
+                    .getStreamExtractor("https://www.youtube.com/watch?v=HoK9shIJ2xQ");
+            extractor.fetchPage();
+        }
+
+        @Test
+        public void testGetFrames() {
+            final StreamFrames frames = extractor.getFrames();
+            assertNotNull(frames);
+            assertNotNull(frames.getDefaultVariant());
+            for (int i=0;i<frames.getVariantsCount();i++) {
+                final StreamFrames.Frameset frameset = frames.getVariant(i);
+                final int pages = frameset.getTotalPages();
+                final String url = pages == 0 ? frameset.getUrl() : frameset.getUrl(pages - 1);
+                assertNotNull(url);
+            }
+        }
+    }
 }