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.

2 files changed, 13 insertions, 1 deletions

diff --git a/packages/meshbay-common/src/meshbay_common/__init__.py b/packages/meshbay-common/src/meshbay_common/__init__.py
index 3ed1ed2..ecf51fd 100644
--- a/packages/meshbay-common/src/meshbay_common/__init__.py
+++ b/packages/meshbay-common/src/meshbay_common/__init__.py
@@ -31,5 +31,11 @@ __version__ = "0.7.0"
 # `thumb_hash`/`display_title` rather than declaring new ones. Additive:
 # an older client simply doesn't render the new fields or send the new
 # messages.
-MNP_VERSION = "0.8"
+# 0.9: added `audio_transcode_req`/`_resp` — WMA and Musepack tag/cover
+# fine but decode in no mainstream browser's <audio> element at all, so
+# the node transcodes to AAC/M4A on request and caches the result the same
+# way a TMDB poster or MusicBrainz cover is cached. Additive: an older
+# client never sends the request, and simply can't play those two formats,
+# same as before this existed.
+MNP_VERSION = "0.9"
 MHP_VERSION = "0.1"
diff --git a/packages/meshbay-common/src/meshbay_common/protocol.py b/packages/meshbay-common/src/meshbay_common/protocol.py
index 3b5d428..8f29c38 100644
--- a/packages/meshbay-common/src/meshbay_common/protocol.py
+++ b/packages/meshbay-common/src/meshbay_common/protocol.py
@@ -113,6 +113,12 @@ class MNP:
     MUSICBRAINZ_ENABLED_ACK = "musicbrainz_enabled_ack"  # node → this group: new enabled state
     MUSIC_META_REQ = "music_meta_req"                    # client → node: metadata for a path
     MUSIC_META_RESP = "music_meta_resp"                  # node → client: metadata (or none)
+    # A file whose format the browser's own <audio> element cannot decode at
+    # all (WMA, Musepack) — resolved to a cached, browser-playable AAC/M4A
+    # copy on request, the same "computed once, reused forever" shape as a
+    # TMDB poster or a MusicBrainz cover.
+    AUDIO_TRANSCODE_REQ = "audio_transcode_req"          # client → node: transcode this file id
+    AUDIO_TRANSCODE_RESP = "audio_transcode_resp"        # node → client: cache hash/size/mime
     # Device linking. A new device files a request bound to a code it displays;
     # an already-pinned device of the same account approves it. Neither the hub
     # nor the node can produce the countersignature.