diff --git a/lib/src/youtube_explode_base.dart b/lib/src/youtube_explode_base.dart
index 4a2daa6..a783da9 100644
--- a/lib/src/youtube_explode_base.dart
+++ b/lib/src/youtube_explode_base.dart
@@ -63,8 +63,10 @@ class YoutubeExplode {
         }
         url ??= Uri.parse(urlString);
 
-        var contentLength =
-            _parseContentLength(streamInfoJson['contentLength'], urlString);
+        var contentLength = await _parseContentLength(
+          streamInfoJson['contentLength'],
+          urlString,
+        );
 
         // Extract container
         var mimeType = MediaType.parse(streamInfoJson['mimeType'] as String);
@@ -125,8 +127,10 @@ class YoutubeExplode {
         }
         url ??= Uri.parse(urlString);
 
-        var contentLength =
-            _parseContentLength(streamInfoJson['contentLength'], urlString);
+        var contentLength = await _parseContentLength(
+          streamInfoJson['contentLength'],
+          urlString,
+        );
 
         // Extract container
         var mimeType = MediaType.parse(streamInfoJson['mimeType'] as String);
@@ -227,7 +231,7 @@ class YoutubeExplode {
           videoInfo['shortDescription'],
           ThumbnailSet(videoId),
           Duration(seconds: int.parse(videoInfo['lengthSeconds'])),
-          videoInfo['keywords'].cast<String>(),
+          videoInfo['keywords']?.cast<String>(),
           Statistics(int.parse(videoInfo['viewCount']), 0, 0));
 
       var streamingData = playerResponseJson['streamingData'];
@@ -293,7 +297,7 @@ class YoutubeExplode {
     var author = details['author'];
     var description = details['shortDescription'];
     var duration = Duration(seconds: int.parse(details['lengthSeconds']));
-    var keyWords = details['keywords'].cast<String>();
+    var keyWords = details['keywords']?.cast<String>();
     var viewCount = int.tryParse(details['viewCount'] ?? '0') ?? 0;
 
     var videoPageHtml = await _getVideoWatchPageHtml(videoId);
@@ -323,18 +327,31 @@ class YoutubeExplode {
         duration, keyWords, statistics);
   }
 
-  int _parseContentLength(String contentLengthString, String url) {
-    var contentLength = int.tryParse(contentLengthString) ?? -1;
+  Future<int> _parseContentLength(
+      String contentLengthString, String url) async {
+    var contentLength = int.tryParse(contentLengthString ?? '') ?? -1;
+
     if (contentLength <= 0) {
       contentLength = _contentLenRegexp?.firstMatch(url)?.group(1) ?? -1;
     }
 
     if (contentLength <= 0) {
-      // TODO: Implement get request to get length.
-//      print('Not implemented');
+      contentLength = await _requestContentLength(url);
+    }
+
+    return contentLength;
+  }
+
+  Future<int> _requestContentLength(String url) async {
+    var resp;
+    try {
+      resp = await http.head(url);
+    } on Exception catch (e) {
       return -1;
     }
-    return contentLength;
+    if (!resp.headers.containsKey('content-length')) return -1;
+    String contentLengthString = resp.headers['content-length'];
+    return int.tryParse(contentLengthString ?? '') ?? -1;
   }
 
   Future<Document> _getVideoWatchPageHtml(String videoId) async {