feat: per-recorder audio_offset_ms dial for A/V alignment

Adds a per-recorder audio offset (ms) control, applied as an ffmpeg -itsoffset
on the audio input: positive delays audio (fixes audio-ahead), negative
advances, 0 = none. Flows DB (migration 037) -> mam-api (RECORDER_FIELDS +
env AUDIO_OFFSET_MS + start body) -> capture.js (sets process.env per session)
-> capture-manager audioOffsetArgs() -> ffmpeg. UI: number field in the
recorder config modal. Verified end-to-end (setting 120 -> -itsoffset 0.1200 on
the live ffmpeg). Default 0, clamped +/-1000ms, non-destructive.

Note: this is an interim trim control; the root-cause A/V fix (Deltacast JOINED
single-slot embedded-audio extraction) is tracked separately.

services/capture/src/routes/capture.js

@@ -330,6 +330,7 @@ router.post('/start', async (req, res) => {
       growing_smb_password,
       growing_smb_vers,
       growing_codec,
+      audio_offset_ms,
     } = req.body;
 
     if (!project_id || !clip_name) {
@@ -415,6 +416,13 @@ router.post('/start', async (req, res) => {
     if (growing_smb_password) process.env.GROWING_SMB_PASSWORD = growing_smb_password;
     if (growing_smb_vers)     process.env.GROWING_SMB_VERS     = growing_smb_vers;
     if (growing_codec)        process.env.GROWING_CODEC        = growing_codec;
+    // Per-recorder A/V trim. Always set (incl. 0) so a standby sidecar that
+    // carried a stale offset from a prior session is reset. capture-manager
+    // reads AUDIO_OFFSET_MS and applies it as -itsoffset on the audio input.
+    if (audio_offset_ms !== undefined && audio_offset_ms !== null)
+      process.env.AUDIO_OFFSET_MS = String(audio_offset_ms);
+    else
+      process.env.AUDIO_OFFSET_MS = '0';
 
     const session = await captureManager.start({
       projectId: project_id,

services/mam-api/src/db/migrations/037-recorder-audio-offset.sql

@@ -0,0 +1,7 @@
+-- 037-recorder-audio-offset.sql
+-- Per-recorder A/V alignment trim. The capture pipeline applies this as an
+-- ffmpeg -itsoffset on the audio input: a POSITIVE value delays audio (use when
+-- audio is ahead of video), NEGATIVE advances it. Clamped to +/-1000 ms in the
+-- API/capture layers. Default 0 = no shift.
+ALTER TABLE recorders
+  ADD COLUMN IF NOT EXISTS audio_offset_ms integer NOT NULL DEFAULT 0;

services/mam-api/src/routes/recorders.js

@@ -155,6 +155,7 @@ const RECORDER_FIELDS = [
   'proxy_container',
   'project_id', 'node_id', 'device_index',
   'growing_enabled', 'growing_codec', 'label',
+  'audio_offset_ms',
 ];
 
 function pickRecorderFields(body) {
@@ -801,6 +802,10 @@ router.post('/:id/start', requireRecorderEdit, async (req, res, next) => {
       `RECORDING_AUDIO_BITRATE=${recorder.recording_audio_bitrate || ''}`,
       `RECORDING_AUDIO_CHANNELS=${recorder.recording_audio_channels ?? 2}`,
       `RECORDING_CONTAINER=${recorder.recording_container || 'mov'}`,
+      // Per-recorder A/V alignment trim. capture-manager applies this as an
+      // -itsoffset on the audio input (positive delays audio = fixes audio-ahead).
+      // Clamped to +/-1000ms. Default 0.
+      `AUDIO_OFFSET_MS=${Math.max(-1000, Math.min(1000, parseInt(recorder.audio_offset_ms, 10) || 0))}`,
 
       // Proxy codec controls
       `PROXY_ENABLED=${recorder.proxy_enabled !== false ? 'true' : 'false'}`,
@@ -919,6 +924,7 @@ router.post('/:id/start', requireRecorderEdit, async (req, res, next) => {
           growing_smb_password:      growingInfra.growing_smb_password || '',
           growing_smb_vers:          growingInfra.growing_smb_vers || '3.0',
           growing_codec:             ['vc3_220','vc3_90'].includes(recorder.growing_codec) ? recorder.growing_codec : 'vc3_90',
+          audio_offset_ms:           Math.max(-1000, Math.min(1000, parseInt(recorder.audio_offset_ms, 10) || 0)),
         };
         const captureRes = await fetch(captureStartUrl, {
           method: 'POST',

services/web-ui/public/screens-ingest.jsx

@@ -627,6 +627,10 @@ function RecorderConfigModal({ recorder, onClose, onSaved }) {
      ['vc3_220','vc3_90'].includes(recorder.growing_codec) ? recorder.growing_codec : 'vc3_90'
    );
    const [projectId, setProjectId] = React.useState(recorder.project_id || PROJECTS[0]?.id || '');
+   // Per-recorder A/V alignment trim (ms). Positive delays audio (fixes audio-ahead).
+   const [audioOffsetMs, setAudioOffsetMs] = React.useState(
+     Number.isFinite(parseInt(recorder.audio_offset_ms, 10)) ? parseInt(recorder.audio_offset_ms, 10) : 0
+   );
    const [saving, setSaving]     = React.useState(false);
    const [err, setErr]           = React.useState(null);
 
@@ -647,6 +651,7 @@ function RecorderConfigModal({ recorder, onClose, onSaved }) {
       growing_enabled: growing,
       growing_codec: growing ? growingCodec : undefined,
       project_id: projectId || null,
+      audio_offset_ms: Math.max(-1000, Math.min(1000, parseInt(audioOffsetMs, 10) || 0)),
     };
     if (showBitrate && bitrate) body.recording_video_bitrate = String(bitrate).replace(/M$/i, '') + 'M';
 
@@ -793,6 +798,19 @@ function RecorderConfigModal({ recorder, onClose, onSaved }) {
             </select>
           </div>
 
+          <div className="field">
+            <label className="field-label">Audio offset (ms)</label>
+            <div style={{ display: 'flex', alignItems: 'center', gap: 8 }}>
+              <input className="field-input" type="number" min="-1000" max="1000" step="1"
+                value={audioOffsetMs} disabled={isRec}
+                onChange={e => setAudioOffsetMs(e.target.value)}
+                style={{ width: 110 }} />
+              <span className="mono" style={{ fontSize: 10.5, color: 'var(--text-3)' }}>
+                + delays audio (use if audio is ahead) · − advances · 0 = none
+              </span>
+            </div>
+          </div>
+
           {err && <div style={{ fontSize: 12, color: 'var(--danger)', marginTop: 4 }}>{err}</div>}
         </div>
         <div className="modal-foot">
@@ -838,6 +856,7 @@ function _normRecorder(r) {
     framerate: r.recording_framerate || 'native',
      growing: r.growing_enabled === true,
      growingCodec: (['vc3_220','vc3_90'].includes(r.growing_codec) ? r.growing_codec : 'vc3_90'),
+     audio_offset_ms: Number.isFinite(parseInt(r.audio_offset_ms, 10)) ? parseInt(r.audio_offset_ms, 10) : 0,
     nodeId: r.node_id || null,
     node: r.node_id ? r.node_id.slice(0, 8) : 'primary',
     deviceIndex: portIdx ?? null,