Android's `audio/opus` MediaCodec encoder emits `BUFFER_FLAG_CODEC_CONFIG`
output buffers BEFORE any audio buffer — typically the 19-byte OpusHead
identification header per RFC 7845, and (on some Codec2 stacks) the
OpusTags comment header. These are decoder-config blobs, NOT audio
frames. We weren't filtering them, so the first 1–2 wire frames every
encoder lifetime were OpusHead bytes wrapped in our legacy-container
varint(timestamp_us) prefix.
The web watcher's WebCodecs `AudioDecoder` handles this by burning
warmup slots (`@moq/watch/src/audio/decoder.ts`'s `warmed <= 3` policy)
— so the listener mostly recovers — but on Android Codec2 stacks that
emit BOTH OpusHead AND OpusTags as separate CSD buffers, two of the
three warmup slots get absorbed by metadata and the listener hears a
tiny click on the next group rollover. The hot-swap path
(`ReconnectingNestsSpeaker`) repeats the warmup on every JWT refresh,
so this fired once every 9 minutes in production.
Filter via `bufferInfo.flags and MediaCodec.BUFFER_FLAG_CODEC_CONFIG`
inside `encode`'s output-drain loop. CSD buffers are released and the
loop continues to the next dequeue rather than returning the bytes.
Logged once per encoder lifetime via `loggedCsdSkip` so we have proof
the path fired without flooding logcat — a stack that emits CSD on
every frame would otherwise be noisy.
Returning `ByteArray(0)` for the first call (because the only output
was a CSD + format-change pair) is unchanged behaviour and the
broadcaster's `if (opus.isEmpty()) continue` already handles it.
https://claude.ai/code/session_014JfZJHSTvyYYWJbC9VbB47
Claude
96cfa1235a