Add a default subtitles track in Google Cast.

src/api/basics/03-using-webvtt.md

@@ -23,7 +23,7 @@ video-subtitles:
     kind: captions
     label: Česky
     src: https://storage.googleapis.com/kino-assets/using-webvtt/cap-cz.vtt
-    srclang: cz
+    srclang: cs
 thumbnail: https://storage.googleapis.com/kino-assets/using-webvtt/thumbnail.png
 media-session-artwork:
   - sizes: 96x96

src/api/streaming/04-streaming-basics.md

@@ -21,7 +21,7 @@ video-subtitles:
     kind: captions
     label: Česky
     src: https://storage.googleapis.com/kino-assets/streaming-basics/cap-cz.vtt
-    srclang: cz
+    srclang: cs
 thumbnail: https://storage.googleapis.com/kino-assets/streaming-basics/thumbnail.png
 media-session-artwork:
   - sizes: 96x96

src/api/streaming/05-efficient-formats.md

@@ -21,7 +21,7 @@ video-subtitles:
     kind: captions
     label: Česky
     src: https://storage.googleapis.com/kino-assets/efficient-formats/cap-cz.vtt
-    srclang: cz
+    srclang: cs
 thumbnail: https://storage.googleapis.com/kino-assets/efficient-formats/thumbnail.png
 media-session-artwork:
   - sizes: 96x96

src/api/streaming/06-adaptive-streaming.md

@@ -21,7 +21,7 @@ video-subtitles:
     kind: captions
     label: Česky
     src: https://storage.googleapis.com/kino-assets/adaptive-streaming/cap-cz.vtt
-    srclang: cz
+    srclang: cs
 thumbnail: https://storage.googleapis.com/kino-assets/adaptive-streaming/thumbnail.png
 media-session-artwork:
   - sizes: 96x96

src/js/web-components/video-player/VideoPlayer.js

@@ -145,6 +145,30 @@ export default class extends HTMLElement {
             metadata.images = [videoThumbnail];
             mediaInfo.metadata = metadata;
 
+            const subtitles = this.internal.videoData['video-subtitles'] || [];
+            const defaultSubtitles = subtitles.find((subtitle) => subtitle.default);
+
+            /**
+             * AFAICT the Default Media Receiver doesn't implement any UI to
+             * select the subtitle track.
+             *
+             * We only add the subtitle track if there is a default one.
+             */
+            if (defaultSubtitles) {
+              const defaultSubtitlesTrack = new window.chrome.cast.media.Track(
+                1,
+                window.chrome.cast.media.TrackType.TEXT,
+              );
+
+              defaultSubtitlesTrack.trackContentId = defaultSubtitles.src;
+              defaultSubtitlesTrack.subtype = window.chrome.cast.media.TextTrackType.SUBTITLES;
+              defaultSubtitlesTrack.name = defaultSubtitles.label;
+              defaultSubtitlesTrack.language = defaultSubtitles.srclang;
+              defaultSubtitlesTrack.trackContentType = 'text/vtt';
+
+              mediaInfo.tracks = [defaultSubtitlesTrack];
+            }
+
             const request = new window.chrome.cast.media.LoadRequest(mediaInfo);
 
             try {