feat(music): transcode WMA/Musepack to AAC so they actually play

Tagging and covers for these two formats landed already, but neither one
decodes in any mainstream browser's <audio> element at all — a real
library scan turned up 273 such files that would show up correctly in the
Music app and then simply fail on click. This closes that gap: the node
transcodes to AAC/M4A on request (a one-shot whole-file conversion, not
live-piped like video's fMP4 segments — an audio file is small enough that
streaming it buys nothing), caches the result under its own content hash
the same way a TMDB poster or a MusicBrainz cover is cached, and serves it
back through the ordinary file_req/chunk path. That path used to assume
anything in the media cache was thumbnail-sized (single chunk, always);
generalized it to slice a cached blob the same way a real file on disk
gets sliced, since a transcoded track can be several MB.

New MNP pair (`audio_transcode_req`/`_resp`, version bump to 0.9), shares
its concurrency cap with video's transcode pool rather than getting its
own — both are real ffmpeg processes on the same node. Every other audio
format is untouched: this only fires for .wma/.mpc, the two extensions
that need it.

1 files changed, 31 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/transport.js b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
index e0e4a64..4f8e3b5 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/transport.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
@@ -620,6 +620,23 @@ class MeshBayTransport {
   }
 
   /**
+   * Server-side transcode of a Music-app file the browser's own <audio>
+   * element cannot decode at all (WMA, Musepack) into AAC/M4A. Returns
+   * `{ hash, size, mime }` — the *cache* hash to pull through the normal
+   * file_req/chunk path (fetchChunk/pipelinedDownload), not the file's own
+   * id, the same indirection already used for a TMDB poster or a
+   * MusicBrainz cover. Cached node-side after the first call, but ffmpeg
+   * still has to run at least once and a transcode slot can be busy, so
+   * this gets a longer timeout than the metadata lookups above.
+   */
+  async requestAudioTranscode(fileId) {
+    const msg = await this._sendAndWait(
+      { type: 'audio_transcode_req', v: '0.9', file_id: fileId }, 120000);
+    if (msg.type === 'error') throw new Error(msg.detail);
+    return msg;
+  }
+
+  /**
    * Set/clear the node-wide MusicBrainz contact string — the User-Agent
    * identity MusicBrainz's usage policy asks for, not a credential (there
    * is none, docs/musicbay.md §3.1). Signed like setTmdbConfig: this turns
@@ -1386,6 +1403,9 @@ class MeshBayTransport {
           // search box can have more than one of these in flight at once.
           : obj.type === 'season_meta_req' ? `season_meta:${obj.tmdb_id}:${obj.season}`
           : obj.type === 'tmdb_search_req' ? `tmdb_search:${obj.media_type}:${obj.query}`
+          // Same reordering hazard as media_meta_req: the player prefetches
+          // the next track while the current one may still be transcoding.
+          : obj.type === 'audio_transcode_req' ? `audio_transcode:${obj.file_id}`
           : null,
         resolve: (msg) => { clearTimeout(timeout); this._pending.delete(id); resolve(msg); },
         reject: (err) => { clearTimeout(timeout); this._pending.delete(id); reject(err); },
@@ -1641,6 +1661,17 @@ class MeshBayTransport {
       return;
     }
 
+    // Same reasoning as music_meta_resp: keyed, not arrival-order — the
+    // player can have a transcode of the current track and a prefetch of
+    // the next one in flight together.
+    if (msg.type === 'audio_transcode_resp') {
+      const key = `audio_transcode:${msg.file_id}`;
+      for (const [, handler] of this._pending) {
+        if (handler._key === key) { handler.resolve(msg); return; }
+      }
+      return;
+    }
+
     // Same reasoning as media_meta_resp: keyed, not arrival-order, and
     // "nobody's waiting any more" must not fall through either.
     if (msg.type === 'season_meta_resp') {