quest(audio-codecs): ADTS export refuses what it cannot label

quest/m1/audio-codecs/README.md

@@ -45,6 +45,7 @@ its own decode and encode quest so verification stays per host.
 
 - [AudioToolbox decode](/quest/m1/audio-codecs/decode-audiotoolbox.md) - macOS and iOS decode HE-AAC, multichannel AAC, and what else the framework offers
 - [Opus surround](/quest/m1/audio-codecs/opus-surround.md) - mapping family 1 decodes on every host through the multistream decoder
+- [ADTS refusals](/quest/m1/audio-codecs/adts-refusals.md) - the ADTS writer refuses channel counts and object types it cannot label instead of mislabeling them
 - [AudioToolbox encode](/quest/m1/audio-codecs/encode-audiotoolbox.md) - macOS and iOS encode AAC-LC
 
 ## Related

quest/m1/audio-codecs/adts-refusals.md

@@ -0,0 +1,25 @@
+# [S] ADTS export refuses what it cannot label
+
+## Goal
+
+`moq-mux`'s ADTS writer never labels an AAC track with the wrong layout or
+object type. A channel count ADTS cannot name is refused, not silently written
+as stereo, and an explicit SBR or PS description is written with the object
+type ADTS can carry or refused, not masked to two bits into a wrong profile.
+
+## Plan
+
+- `channel_config_from_count` falls back to stereo for counts it cannot
+  represent; refuse instead, the same way #4178 made channelConfiguration 11 to
+  14 refuse.
+- The ADTS header masks the object type to two bits, so an explicit HE-AAC
+  (object type 5) or HE-AACv2 (29) description is mislabeled. Decide per case:
+  signal the backward-compatible AAC-LC core (implicit SBR) when the description
+  allows it, otherwise refuse.
+- Tests for both with real fixtures, checked against ffprobe.
+
+Public API: none. Wire: none; TS output changes only for inputs it mislabeled.
+
+## Related
+
+- [#4178](https://github.com/moq-dev/moq/pull/4178) - the PCE export that found these