feat(cast): music on the TV, the music bar as its remote

A cast button in Music's toolbar and in the music bar. With a television
chosen, each decrypted track goes to the relay with its cover — found as the
album card finds it — and plays there as music with its title, artist and
album; the bar's play, pause, seek, previous and next drive the receiver, its
clock is the receiver's, and the end of a track there moves the queue on.
A film or a photo taking the television pauses the bar; stopping the cast
carries the track on locally.

Photos and tracks now share one path: a whole file sent to the relay in
pieces (binary frames on Android, written to disk there), served at /file
with byte ranges and its cover at /cover, and loaded as what the relay says
it is. cast:image is gone; cast:chromecast:seek is new.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 37 insertions, 11 deletions

diff --git a/packages/meshbay-client/src/cast-chromecast.js b/packages/meshbay-client/src/cast-chromecast.js
index 4c8ddf0..8c6c9c6 100644
--- a/packages/meshbay-client/src/cast-chromecast.js
+++ b/packages/meshbay-client/src/cast-chromecast.js
@@ -42,17 +42,30 @@ const TEXT_TRACK_STYLE = Object.freeze({
 
 /**
  * What to hand `player.load()` for a stream, with or without subtitles, or
- * for a photo.
+ * for a whole file the relay serves.
  *
  * `streamType: 'LIVE'` because the relay has no beginning to seek back to —
  * the film's own timeline lives on this side, and a seek restarts the relay.
- * A photo is not a stream at all.
+ * A file is the relay's to describe (`file`: its type and what to show with
+ * it), never the page's: a photo is not a stream at all, and a music track is
+ * an ordinary buffered file the receiver seeks in itself.
  */
-function mediaFor(mediaUrl, subtitle, contentType) {
-  if (contentType && contentType.startsWith('image/')) {
-    return { contentId: mediaUrl, contentType, streamType: 'NONE',
+function mediaFor(mediaUrl, subtitle, file) {
+  if (file && file.contentType.startsWith('image/')) {
+    return { contentId: mediaUrl, contentType: file.contentType, streamType: 'NONE',
              metadata: { metadataType: 4 } };   // PhotoMediaMetadata
   }
+  if (file) {
+    const meta = file.meta || {};
+    return {
+      contentId: mediaUrl, contentType: file.contentType, streamType: 'BUFFERED',
+      metadata: {
+        metadataType: 3,                         // MusicTrackMediaMetadata
+        title: meta.title || '', artist: meta.artist || '', albumName: meta.album || '',
+        images: meta.cover ? [{ url: meta.cover }] : [],
+      },
+    };
+  }
   const media = {
     contentId: mediaUrl,
     contentType: 'video/mp4',
@@ -73,11 +86,14 @@ function mediaFor(mediaUrl, subtitle, contentType) {
   return media;
 }
 
-function loadOptionsFor(subtitle) {
-  return {
+function loadOptionsFor(subtitle, startAt) {
+  const options = {
     autoplay: true,
     activeTrackIds: subtitle && subtitle.url ? [TEXT_TRACK_ID] : [],
   };
+  // Where in a track to begin: a cast started mid-song carries on from there.
+  if (startAt > 0) options.currentTime = startAt;
+  return options;
 }
 
 class CastChromecast {
@@ -145,7 +161,7 @@ class CastChromecast {
     }
   }
 
-  async connect(deviceId, mediaUrl, subtitle, contentType) {
+  async connect(deviceId, mediaUrl, subtitle, file, startAt) {
     const device = this._devices.get(deviceId);
     if (!device) throw new Error(`Unknown device: ${deviceId}`);
 
@@ -185,7 +201,7 @@ class CastChromecast {
 
     debug(`[cast-chromecast] loading with ${subtitle?.url ? 'subtitles' : 'no subtitles'}`);
     const status = await new Promise((resolve, reject) => {
-      player.load(mediaFor(mediaUrl, subtitle, contentType), loadOptionsFor(subtitle),
+      player.load(mediaFor(mediaUrl, subtitle, file), loadOptionsFor(subtitle, startAt),
         (err, s) => {
           if (err) return reject(err);
           resolve(s);
@@ -197,12 +213,12 @@ class CastChromecast {
     return { deviceName: device.name, playerState: status.playerState };
   }
 
-  async reload(mediaUrl, subtitle, contentType) {
+  async reload(mediaUrl, subtitle, file, startAt) {
     if (!this._player) throw new Error('Not connected');
     debug(`[cast-chromecast] reloading stream on "${this._connectedDevice?.name}"`
       + ` with ${subtitle?.url ? 'subtitles' : 'no subtitles'}`);
     const status = await new Promise((resolve, reject) => {
-      this._player.load(mediaFor(mediaUrl, subtitle, contentType), loadOptionsFor(subtitle),
+      this._player.load(mediaFor(mediaUrl, subtitle, file), loadOptionsFor(subtitle, startAt),
         (err, s) => {
           if (err) return reject(err);
           resolve(s);
@@ -256,6 +272,16 @@ class CastChromecast {
     return { playerState: status && status.playerState };
   }
 
+  /** Where in a track the receiver should be; a film seeks by restarting the relay instead. */
+  async seek(seconds) {
+    if (!this._player) throw new Error('Not connected');
+    const status = await new Promise((resolve, reject) => {
+      this._player.seek(Math.max(0, Number(seconds) || 0), (err, s) => (err ? reject(err) : resolve(s)));
+    });
+    this._noteStatus(status);
+    return { playerState: status && status.playerState };
+  }
+
   async play() {
     if (!this._player) throw new Error('Not connected');
     const status = await new Promise((resolve, reject) => {