Call pre-connect urls before gvideo url

src/main/java/com/sedmelluq/discord/lavaplayer/source/youtube/YoutubeAudioSourceManager.java

@@ -106,6 +106,8 @@ public YoutubeAudioSourceManager(boolean allowSearch, HttpRoutePlanner routePlan
     signatureCipherManager = new YoutubeSignatureCipherManager();
 
     HttpRequestModifier requestModifier = request -> {
+      if(request.getURI().toString().contains("generate_204"))
+        return;
       request.setHeader("x-youtube-client-name", "1");
       request.setHeader("x-youtube-client-version", "2.20191008.04.01");
     };
@@ -221,12 +223,12 @@ private AudioItem loadItemOnce(AudioReference reference) {
    */
   public AudioItem loadTrackWithVideoId(String videoId, boolean mustExist) {
     try (HttpInterface httpInterface = getHttpInterface()) {
-      JsonBrowser info = getTrackInfoFromMainPage(httpInterface, videoId, mustExist);
-      if (info == null) {
+        final YoutubeJsonResponse jsonResponse = getTrackInfoFromMainPage(httpInterface, videoId, mustExist);
+        if (jsonResponse.getPlayerInfo() == null) {
         return AudioReference.NO_TRACK;
       }
 
-      JsonBrowser args = info.get("args");
+      JsonBrowser args = jsonResponse.getPlayerInfo().get("args");
       boolean useOldFormat = args.get("player_response").isNull();
 
       if (useOldFormat) {
@@ -380,7 +382,7 @@ private AudioItem loadLinkedPlaylistWithId(String playlistId, String videoId) {
    *         <code>false</code>.
    * @throws IOException On network error.
    */
-  public JsonBrowser getTrackInfoFromMainPage(HttpInterface httpInterface, String videoId, boolean mustExist) throws IOException {
+  public YoutubeJsonResponse getTrackInfoFromMainPage(HttpInterface httpInterface, String videoId, boolean mustExist) throws IOException {
     String url = getWatchUrl(videoId) + "&pbj=1&hl=en";
 
     try (CloseableHttpResponse response = httpInterface.execute(new HttpGet(url))) {
@@ -396,10 +398,13 @@ public JsonBrowser getTrackInfoFromMainPage(HttpInterface httpInterface, String
         JsonBrowser json = JsonBrowser.parse(responseText);
         JsonBrowser playerInfo = null;
         JsonBrowser statusBlock = null;
+        JsonBrowser preConnectUrls = null;
 
         for (JsonBrowser child : json.values()) {
           if (child.isMap()) {
-            if (!child.get("player").isNull()) {
+            if(!child.get("preconnect").isNull()) {
+              preConnectUrls = child.get("preconnect");
+            } else if (!child.get("player").isNull()) {
               playerInfo = child.get("player");
             } else if (!child.get("playerResponse").isNull()) {
               statusBlock = child.get("playerResponse").safeGet("playabilityStatus");
@@ -413,7 +418,7 @@ public JsonBrowser getTrackInfoFromMainPage(HttpInterface httpInterface, String
           throw new RuntimeException("No player info block.");
         }
 
-        return playerInfo;
+        return new YoutubeJsonResponse(playerInfo, preConnectUrls);
       } catch (Exception e) {
         throw new FriendlyException("Received unexpected response from YouTube.", SUSPICIOUS,
             new RuntimeException("Failed to parse: " + responseText, e));
@@ -626,6 +631,32 @@ private static UrlInfo getUrlInfo(String url, boolean retryValidPart) {
     }
   }
 
+  static class YoutubeJsonResponse {
+    private final JsonBrowser playerInfo;
+    private final String[] preConnectUrls;
+
+    private YoutubeJsonResponse(final JsonBrowser player, final JsonBrowser preConnectUrls) {
+      this.playerInfo = player;
+      if(preConnectUrls == null) {
+        this.preConnectUrls = new String[0];
+        return;
+      }
+      final List<JsonBrowser> entries = preConnectUrls.values();
+      this.preConnectUrls = new String[entries.size()];
+      for (int i = 0; i < entries.size(); i++) {
+        this.preConnectUrls[i] = entries.get(i).as(String.class);
+      }
+    }
+
+      public JsonBrowser getPlayerInfo() {
+          return playerInfo;
+      }
+
+      public String[] getPreConnectUrls() {
+          return preConnectUrls;
+      }
+  }
+
   private static class UrlInfo {
     private final String path;
     private final Map<String, String> parameters;

src/main/java/com/sedmelluq/discord/lavaplayer/source/youtube/YoutubeAudioTrack.java

@@ -54,15 +54,16 @@ public class YoutubeAudioTrack extends DelegatedAudioTrack {
           .build();
 
   private final YoutubeAudioSourceManager sourceManager;
+  private final String refererUrl;
 
   /**
    * @param trackInfo Track info
    * @param sourceManager Source manager which was used to find this track
    */
   public YoutubeAudioTrack(AudioTrackInfo trackInfo, YoutubeAudioSourceManager sourceManager) {
     super(trackInfo);
-
     this.sourceManager = sourceManager;
+    this.refererUrl = "https://www.youtube.com/watch?v=" + trackInfo.identifier;
   }
 
   @Override
@@ -126,16 +127,19 @@ private Tuple<FormatWithUrl, Boolean> loadBestFormatWithUrl(HttpInterface httpIn
       return new Tuple<>(cachedPlaybackFormat, true);
     }
 
-    JsonBrowser info = getTrackInfo(httpInterface);
+    final YoutubeAudioSourceManager.YoutubeJsonResponse jsonResponse = getTrackInfo(httpInterface);
 
-    String playerScript = extractPlayerScriptFromInfo(info);
-    List<YoutubeTrackFormat> formats = loadTrackFormats(info, httpInterface, playerScript);
+    String playerScript = extractPlayerScriptFromInfo(jsonResponse.getPlayerInfo());
+    List<YoutubeTrackFormat> formats = loadTrackFormats(jsonResponse.getPlayerInfo(), httpInterface, playerScript);
     YoutubeTrackFormat format = findBestSupportedFormat(formats);
 
     URI signedUrl = sourceManager.getCipherManager().getValidUrl(httpInterface, playerScript, format);
     FormatWithUrl bestFormat = new FormatWithUrl(format, signedUrl);
 
     playbackFormatCache.put(videoId, bestFormat);
+
+    callPreconnectUrls(httpInterface, jsonResponse.getPreConnectUrls());
+
     return new Tuple<>(bestFormat, false);
   }
 
@@ -149,7 +153,17 @@ public AudioSourceManager getSourceManager() {
     return sourceManager;
   }
 
-  private JsonBrowser getTrackInfo(HttpInterface httpInterface) throws Exception {
+  private void callPreconnectUrls(final HttpInterface httpInterface, final String[] preConnectUrls) throws IOException {
+    for (final String url : preConnectUrls) {
+      final HttpGet httpGet = new HttpGet(url);
+      httpGet.setHeader("Accept", "image/webp, */*");
+      httpGet.setHeader("Referer", this.refererUrl);
+      final CloseableHttpResponse response = httpInterface.execute(httpGet);
+      response.close();
+    }
+  }
+
+  private YoutubeAudioSourceManager.YoutubeJsonResponse getTrackInfo(HttpInterface httpInterface) throws Exception {
     return sourceManager.getTrackInfoFromMainPage(httpInterface, getIdentifier(), true);
   }