Videos: Append '&mpd_version=5' to DASH manifest URL

This makes Youtube return a MPD manifest with templates rather than
lengthy <SegmentList>. The returned  manifest is about 44 times smaller.

src/invidious/videos.cr

@@ -227,8 +227,22 @@ struct Video
     info.dig?("streamingData", "hlsManifestUrl").try &.as_s
   end
 
-  def dash_manifest_url
-    info.dig?("streamingData", "dashManifestUrl").try &.as_s
+  def dash_manifest_url : String?
+    raw_dash_url = info.dig?("streamingData", "dashManifestUrl").try &.as_s
+    return nil if raw_dash_url.nil?
+
+    # Use manifest v5 parameter to reduce file size
+    # See https://github.com/iv-org/invidious/issues/4186
+    dash_url = URI.parse(raw_dash_url)
+    dash_query = dash_url.query || ""
+
+    if dash_query.empty?
+      dash_url.path = "#{dash_url.path}/mpd_version/5"
+    else
+      dash_url.query = "#{dash_query}&mpd_version=5"
+    end
+
+    return dash_url.to_s
   end
 
   def genre_url : String?