Fix recording truncation and rate mismatch causing static

The recording pipeline had two bugs that combined to produce
buzzing/static in recorded audio:

1. NormalizeStereoFrame truncated incoming audio frames to
   frameSize*AudioChannels samples. When the Opus decoder produced
   20ms frames (1920 stereo samples) but the recorder used a 10ms
   frameSize (960 samples), half the audio from every packet was
   silently dropped.

2. The recorder's run() loop dequeued one fixed-length frame per
   source per tick. After truncation, the remaining 10ms of each
   20ms packet was gone, so every other tick produced silence.
   This 50 Hz on/off pattern sounded like static.

Fixes:
- NormalizeStereoFrame no longer truncates; it only converts mono
  to stereo and preserves all audio data
- RecordAudioFrame now accepts an explicit stereo flag from callers
  instead of guessing from sample count (which failed for even-length
  mono data like 480-sample mic frames)
- run() accumulates variable-length frames per source and consumes
  them in fixed-size chunks, preserving any leftover for the next tick

gumble/gumbleopenal/stream.go

@@ -45,7 +45,7 @@ type FilePlayer interface {
 }
 
 type Recorder interface {
-	RecordAudioFrame(source uint32, samples []int16)
+	RecordAudioFrame(source uint32, samples []int16, stereo bool)
 }
 
 const recorderOutgoingSource uint32 = ^uint32(0)
@@ -742,7 +742,7 @@ func (s *Stream) processAudioPacket(packet *gumble.AudioPacket, user *gumble.Use
 		}
 	}
 	if recorder != nil && recordPtr > 0 {
-		recorder.RecordAudioFrame(user.Session, recordBuffer[:recordPtr])
+		recorder.RecordAudioFrame(user.Session, recordBuffer[:recordPtr], true)
 	}
 
 	if len(emptyBufs) == 0 {
@@ -932,7 +932,7 @@ func (s *Stream) sourceRoutine(inputDevice *string, stop chan bool, done chan st
 				// Send stereo buffer when file is playing
 				outgoing <- gumble.AudioBuffer(outputBuffer)
 				if recorder := s.getRecorder(); recorder != nil {
-					recorder.RecordAudioFrame(recorderOutgoingSource, outputBuffer)
+					recorder.RecordAudioFrame(recorderOutgoingSource, outputBuffer, true)
 				}
 			} else if hasMicInput {
 				// Send mic when no file is playing. If the microphone is
@@ -949,7 +949,7 @@ func (s *Stream) sourceRoutine(inputDevice *string, stop chan bool, done chan st
 				}
 				outgoing <- gumble.AudioBuffer(outBuf)
 				if recorder := s.getRecorder(); recorder != nil {
-					recorder.RecordAudioFrame(recorderOutgoingSource, outBuf)
+					recorder.RecordAudioFrame(recorderOutgoingSource, outBuf, false)
 				}
 			}
 		}

recording/recorder.go

@@ -152,14 +152,14 @@ func (r *Recorder) Path() string {
 	return r.path
 }
 
-func (r *Recorder) RecordAudioFrame(source uint32, samples []int16) {
+func (r *Recorder) RecordAudioFrame(source uint32, samples []int16, stereo bool) {
 	if r == nil || len(samples) == 0 {
 		return
 	}
 	if len(r.input) >= cap(r.input) {
 		return
 	}
-	frame := NormalizeStereoFrame(samples, r.frameSize)
+	frame := NormalizeStereoFrame(samples, stereo)
 	select {
 	case r.input <- sourceFrame{source: source, samples: frame}:
 	default:
@@ -192,31 +192,35 @@ func (r *Recorder) run() {
 	defer close(r.done)
 	ticker := time.NewTicker(r.interval)
 	defer ticker.Stop()
-	queues := make(map[uint32][][]int16)
-	frame := make([]int16, r.frameSize*gumble.AudioChannels)
+	// Per-source accumulated stereo samples. Incoming frames of any size are
+	// appended and then consumed in frameSize*AudioChannels chunks each tick.
+	queues := make(map[uint32][]int16)
+	chunkSize := r.frameSize * gumble.AudioChannels
+	chunk := make([]int16, chunkSize)
 	for {
 		select {
 		case <-r.stop:
 			r.closeEncoder()
 			return
 		case item := <-r.input:
-			queues[item.source] = append(queues[item.source], item.samples)
+			queues[item.source] = append(queues[item.source], item.samples...)
 		case <-ticker.C:
-			clear(frame)
-			for source, queue := range queues {
-				if len(queue) == 0 {
+			clear(chunk)
+			for source, buffer := range queues {
+				if len(buffer) == 0 {
 					delete(queues, source)
 					continue
 				}
-				mix(frame, queue[0])
-				queue = queue[1:]
-				if len(queue) == 0 {
+				// Mix one chunk worth of samples from this source.
+				if len(buffer) <= chunkSize {
+					mix(chunk, buffer)
 					delete(queues, source)
 				} else {
-					queues[source] = queue
+					mix(chunk, buffer[:chunkSize])
+					queues[source] = buffer[chunkSize:]
 				}
 			}
-			if err := writePCM(r.stdin, frame); err != nil {
+			if err := writePCM(r.stdin, chunk); err != nil {
 				r.setError(err)
 				r.closeEncoder()
 				return
@@ -248,19 +252,19 @@ func (r *Recorder) setError(err error) {
 	}
 }
 
-func NormalizeStereoFrame(samples []int16, frameSize int) []int16 {
-	out := make([]int16, frameSize*gumble.AudioChannels)
-	if len(samples) >= frameSize*gumble.AudioChannels && len(samples)%gumble.AudioChannels == 0 {
-		copy(out, samples[:frameSize*gumble.AudioChannels])
-		return out
+// NormalizeStereoFrame ensures samples are in stereo interleaved format.
+// If stereo is true the samples are returned as-is (already interleaved).
+// Mono input is duplicated to both channels. The returned slice preserves
+// all input audio without truncation.
+func NormalizeStereoFrame(samples []int16, stereo bool) []int16 {
+	if stereo {
+		return samples
 	}
-	limit := frameSize
-	if len(samples) < limit {
-		limit = len(samples)
-	}
-	for i := 0; i < limit; i++ {
-		out[i*2] = samples[i]
-		out[i*2+1] = samples[i]
+	// Convert mono to stereo by duplicating each sample.
+	out := make([]int16, len(samples)*gumble.AudioChannels)
+	for i, s := range samples {
+		out[i*2] = s
+		out[i*2+1] = s
 	}
 	return out
 }

recording/recorder_test.go

@@ -93,16 +93,36 @@ func TestReservePathPreventsConcurrentRecordingCollisions(t *testing.T) {
 }
 
 func TestNormalizeStereoFrame(t *testing.T) {
-	mono := NormalizeStereoFrame([]int16{1, -2}, 3)
-	wantMono := []int16{1, 1, -2, -2, 0, 0}
+	// Mono input duplicating each sample to both channels.
+	mono := NormalizeStereoFrame([]int16{1, -2, 3}, false)
+	wantMono := []int16{1, 1, -2, -2, 3, 3}
+	if len(mono) != len(wantMono) {
+		t.Fatalf("mono len = %d, want %d", len(mono), len(wantMono))
+	}
 	for i := range wantMono {
 		if mono[i] != wantMono[i] {
 			t.Fatalf("mono[%d] = %d, want %d", i, mono[i], wantMono[i])
 		}
 	}
 
-	stereo := NormalizeStereoFrame([]int16{1, 2, 3, 4, 5, 6}, 2)
-	wantStereo := []int16{1, 2, 3, 4}
+	// Even-length mono must not be mistaken for stereo.
+	monoEven := NormalizeStereoFrame([]int16{1, -2}, false)
+	wantMonoEven := []int16{1, 1, -2, -2}
+	if len(monoEven) != len(wantMonoEven) {
+		t.Fatalf("monoEven len = %d, want %d", len(monoEven), len(wantMonoEven))
+	}
+	for i := range wantMonoEven {
+		if monoEven[i] != wantMonoEven[i] {
+			t.Fatalf("monoEven[%d] = %d, want %d", i, monoEven[i], wantMonoEven[i])
+		}
+	}
+
+	// Stereo input passes through unchanged.
+	stereo := NormalizeStereoFrame([]int16{1, 2, 3, 4, 5, 6}, true)
+	wantStereo := []int16{1, 2, 3, 4, 5, 6}
+	if len(stereo) != len(wantStereo) {
+		t.Fatalf("stereo len = %d, want %d", len(stereo), len(wantStereo))
+	}
 	for i := range wantStereo {
 		if stereo[i] != wantStereo[i] {
 			t.Fatalf("stereo[%d] = %d, want %d", i, stereo[i], wantStereo[i])