TASK 22: global audio sync offset (positive delay at the mixer out)

Adds AudioSyncOffsetMs (0..500ms, default 0) that delays the whole interleaved-stereo mix so audio lands on the video when it runs ahead — OBS's documented lip-sync fix. Positive-only: advancing audio needs a video-side delay and is out of the audio layer's scope. - Services/Audio/AudioSyncDelay.cs: pure delay line, flushed on Configure - AudioMixer: Func<int> syncOffsetMs seam + delay applied post-limiter - LayoutStore.Settings + MainViewModel.Audio/VM: load/save + binding - PreviewPane mic bar: SYNC slider + status dot (IntToSyncBrushConverter) - AudioSyncDelayTests: identity, negative/beyond-500 clamps, 10ms→960 samples Reference (external scan): https://obs-versions.com/blog/how-to-fix-audio-delay-on-obs (audio ahead => positive delay). Verified: build 0 warnings; 3/3 delay tests pass.
2026-08-31 18:30:03 -07:00
parent 670fe3a10a
commit e8ff4df05f
12 changed files with 295 additions and 128 deletions
@@ -0,0 +1,77 @@
+using Xunit;
+using ytLive.Services.Audio;
+
+namespace ytLive.Tests;
+
+/// <summary>
+/// TASK 22: the global audio-sync delay line. It is a pure fixed positive
+/// delay on the interleaved stereo mix — the OBS fix for audio running ahead
+/// of video. Positive-only: advancing audio needs a video-side delay and is
+/// out of the audio layer's scope.
+/// </summary>
+public class AudioSyncDelayTests
+{
+    [Fact]
+    public void ZeroDelay_PassesThroughUnchanged()
+    {
+        var delay = new AudioSyncDelay(48000);
+        delay.Configure(0);
+
+        var input = new float[16];
+        for (var i = 0; i < input.Length; i++)
+            input[i] = i - 8;
+        var output = new float[16];
+
+        delay.Process(input, output);
+
+        Assert.Equal(input, output);
+    }
+
+    [Fact]
+    public void ConfigureClampsNegativeToZero_AndBeyond500msTo500ms()
+    {
+        var delay = new AudioSyncDelay(48000);
+        delay.Configure(-50);
+        Assert.Equal(0, MarkerShift(delay, 1000));
+
+        // 500 ms at 48 kHz = 24000 frames = 48000 interleaved samples.
+        delay.Configure(6000);
+        Assert.Equal(48000, MarkerShift(delay, 48000));
+    }
+
+    [Fact]
+    public void TenMsDelay_EmitsTheSignal960SamplesLater()
+    {
+        // 10 ms at 48 kHz = 480 frames; interleaved stereo = 960 samples.
+        var delay = new AudioSyncDelay(48000);
+        Assert.Equal(960, MarkerShift(delay, 480 * 2, configureMs: 10));
+    }
+
+    private static int MarkerShift(AudioSyncDelay delay, int chunkLen, int configureMs = -1)
+    {
+        if (configureMs >= 0)
+            delay.Configure(configureMs);
+
+        var chunk = new float[chunkLen];
+        var output = new float[chunkLen];
+        chunk[0] = 1f; // sole non-zero: left of frame 0
+
+        var foundAt = -1;
+        var total = 0;
+        for (var c = 0; c < 4 && foundAt < 0; c++)
+        {
+            delay.Process(chunk, output);
+            for (var i = 0; i < chunkLen; i++)
+            {
+                if (output[i] != 0f)
+                {
+                    foundAt = total + i;
+                    break;
+                }
+            }
+            total += chunkLen;
+        }
+        Assert.True(foundAt >= 0, "marker never appeared in the delayed output");
+        return foundAt;
+    }
+}