Remove demo signal generator

Audio capture only — shows NO SIGNAL when libav can't connect.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/osc.nim

@@ -66,8 +66,6 @@ proc main() =
         of gsGrid: gsCross
         of gsCross: gsOff
         of gsOff: gsGrid
-    of Key.D:
-      audio.cyclePreset()
     else:
       discard
 

src/osc/audio.nim

@@ -1,7 +1,6 @@
-## Audio capture via libavdevice/libavformat (dlopen at runtime),
+## Audio capture via libavdevice/libavformat (dlopen at runtime).
-## with fallback to demo signal.
 
-import osproc, strutils, math
+import osproc, strutils
 import scope
 
 # ── libav C helper bindings ──────────────────────────────────────────
@@ -10,8 +9,8 @@ import scope
 {.passL: "-ldl".}
 
 type
-  AVFormatContext = object  # opaque, only used as pointer
+  AVFormatContext = object
-  AVPacket = object         # opaque, only used as pointer
+  AVPacket = object
 
 proc av_helper_init(): cint {.importc, cdecl.}
 proc av_helper_open_pulse(ctx: ptr ptr AVFormatContext,
@@ -46,102 +45,62 @@ proc findMonitorSource(): string =
   except: discard
   ""
 
-# ── Audio capture types ──────────────────────────────────────────────
+# ── Audio capture ────────────────────────────────────────────────────
 
 type
-  AudioMode* = enum
-    amLive   ## Direct libav capture
-    amDemo   ## Built-in synthesized waveforms
-
   AudioCapture* = object
-    mode*: AudioMode
     fmtCtx: ptr AVFormatContext
     packet: ptr AVPacket
     streamIdx: cint
-    phase: float
+    live*: bool
-    demoFreqL*, demoFreqR*: float
-    demoPreset*: int
-
-# ── Start / stop ─────────────────────────────────────────────────────
 
 proc startAudio*(): AudioCapture =
   let monitor = findMonitorSource()
-  if monitor.len > 0:
+  if monitor.len == 0: return
-    block libav:
-      if av_helper_init() < 0: break libav
-      var ctx: ptr AVFormatContext = nil
-      if av_helper_open_pulse(addr ctx, monitor.cstring) < 0: break libav
-      if av_helper_find_stream_info(ctx) < 0:
-        av_helper_close(addr ctx)
-        break libav
-      let idx = av_helper_find_audio_stream(ctx)
-      let pkt = av_helper_packet_alloc()
-      if pkt != nil:
-        return AudioCapture(
-          mode: amLive, fmtCtx: ctx, packet: pkt,
-          streamIdx: idx.cint,
-          demoFreqL: 440.0, demoFreqR: 330.0)
-      av_helper_close(addr ctx)
 
-  AudioCapture(mode: amDemo, demoFreqL: 440.0, demoFreqR: 330.0)
+  if av_helper_init() < 0: return
+
+  var ctx: ptr AVFormatContext = nil
+  if av_helper_open_pulse(addr ctx, monitor.cstring) < 0: return
+  if av_helper_find_stream_info(ctx) < 0:
+    av_helper_close(addr ctx)
+    return
+
+  let idx = av_helper_find_audio_stream(ctx)
+  let pkt = av_helper_packet_alloc()
+  if pkt == nil:
+    av_helper_close(addr ctx)
+    return
+
+  AudioCapture(fmtCtx: ctx, packet: pkt, streamIdx: idx.cint, live: true)
 
 proc stop*(cap: var AudioCapture) =
-  if cap.mode == amLive:
+  if cap.live:
     if cap.packet != nil: av_helper_packet_free(addr cap.packet)
     if cap.fmtCtx != nil: av_helper_close(addr cap.fmtCtx)
 
 proc sourceLabel*(cap: AudioCapture): string =
-  if cap.mode == amLive: "LIVE" else: "DEMO"
+  if cap.live: "LIVE" else: "NO SIGNAL"
-
-# ── Preset cycling ───────────────────────────────────────────────────
-
-proc cyclePreset*(cap: var AudioCapture) =
-  if cap.mode != amDemo: return
-  cap.demoPreset = (cap.demoPreset + 1) mod 4
-  case cap.demoPreset
-  of 0: cap.demoFreqL = 440.0; cap.demoFreqR = 330.0   # 4:3
-  of 1: cap.demoFreqL = 440.0; cap.demoFreqR = 440.0   # 1:1
-  of 2: cap.demoFreqL = 440.0; cap.demoFreqR = 220.0   # 2:1
-  of 3: cap.demoFreqL = 440.0; cap.demoFreqR = 293.3   # 3:2
-  else: discard
-
-# ── Sample reading ───────────────────────────────────────────────────
 
 proc readSamples*(cap: var AudioCapture, scope: var Scope) =
-  case cap.mode
+  if not cap.live: return
-  of amLive:
-    const frameSize = 4  # 2ch × 16-bit
-    var totalSamples = 0
-    while totalSamples < scope.samplesL.len:
-      let ret = av_helper_read_frame(cap.fmtCtx, cap.packet)
-      if ret < 0: break
-      if av_helper_packet_stream(cap.packet) == cap.streamIdx:
-        let data = av_helper_packet_data(cap.packet)
-        let size = av_helper_packet_size(cap.packet)
-        let frames = size div frameSize
-        for i in 0..<frames:
-          if totalSamples >= scope.samplesL.len: break
-          let off = i * frameSize
-          let left = cast[int16]((data[off + 1].uint16 shl 8) or data[off].uint16)
-          let right = cast[int16]((data[off + 3].uint16 shl 8) or data[off + 2].uint16)
-          scope.samplesL[totalSamples] = left.float / 32768.0
-          scope.samplesR[totalSamples] = right.float / 32768.0
-          totalSamples += 1
-      av_helper_packet_unref(cap.packet)
-      if totalSamples > 0: break
-    scope.sampleCount = totalSamples
 
-  of amDemo:
+  const frameSize = 4  # 2ch × 16-bit
-    scope.sampleCount = scope.samplesL.len
+  var total = 0
-    let cycles = 3.0 / scope.timeDiv
+  while total < scope.samplesL.len:
-    let drift = sin(cap.phase * 0.3) * 0.1
+    let ret = av_helper_read_frame(cap.fmtCtx, cap.packet)
-    let rL = cap.demoFreqL / 440.0
+    if ret < 0: break
-    let rR = cap.demoFreqR / 440.0
+    if av_helper_packet_stream(cap.packet) == cap.streamIdx:
-    for i in 0..<scope.sampleCount:
+      let data = av_helper_packet_data(cap.packet)
-      let t = cap.phase + (i.float / scope.sampleCount.float) * cycles * 2.0 * PI
+      let size = av_helper_packet_size(cap.packet)
-      scope.samplesL[i] = sin(t * rL) * 0.7 +
+      for i in 0..<(size div frameSize):
-                           sin(t * rL * 2.0) * 0.15 +
+        if total >= scope.samplesL.len: break
-                           sin(t * rL * 3.0 + drift) * 0.08
+        let off = i * frameSize
-      scope.samplesR[i] = sin(t * rR + 0.5) * 0.7 +
+        let left = cast[int16]((data[off + 1].uint16 shl 8) or data[off].uint16)
-                           sin(t * rR * 2.0 + 0.3) * 0.2
+        let right = cast[int16]((data[off + 3].uint16 shl 8) or data[off + 2].uint16)
-    cap.phase += 0.05
+        scope.samplesL[total] = left.float / 32768.0
+        scope.samplesR[total] = right.float / 32768.0
+        total += 1
+    av_helper_packet_unref(cap.packet)
+    if total > 0: break
+  scope.sampleCount = total