fix(worker): conform — lock fps + sample rate in concat filter graph

After the demuxer → filter switch, concat still failed with
  [fc#0] Error sending frames to consumers: Invalid argument
on Job 8. The filter graph normalised pixels (scale+pad+yuv420p) but
left the time-domain axes mixed:

  segment-1: 23.98 fps video, 44100 Hz audio
  segment-2: 60    fps video, 48000 Hz audio
  segment-3: …

ffmpeg 8's concat filter requires identical frame rate + audio sample
rate + channel layout across inputs. Force them on each leg:

  video: fps=<seqFps>, setpts=PTS-STARTPTS
  audio: aresample=48000,
         aformat=channel_layouts=stereo:sample_fmts=fltp,
         asetpts=PTS-STARTPTS

setpts/asetpts re-zero each input's clock so concat's per-input PTS
window resets cleanly between segments.

Target fps comes from the sequence's frame_rate (rounded) — same axis
the sequence editor stores. Sample rate is pinned to 48000 (broadcast
standard) so the AAC encode is consistent.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

services/worker/src/workers/conform.js

@@ -282,29 +282,44 @@ export const conformWorker = async (job) => {
     const inputArgs = [];
     concatList.forEach(p => { inputArgs.push('-i', p); });
 
-    // Build the filter graph: scale each video stream to a consistent
+    // Build the filter graph. The concat filter in ffmpeg 8.x requires
-    // resolution + pixel format, then concat them. The audio leg only
+    // identical resolution, pixel format, SAR, FRAME RATE and audio
-    // runs if audio is being kept.
+    // SAMPLE RATE / CHANNEL LAYOUT across all inputs. Different-spec
-    const targetW = isProRes ? 1920 : 1920;
+    // sources (e.g. a 23.98 fps clip + a 60 fps clip) trip
+    //   [fc#0] Error sending frames to consumers: Invalid argument
+    // even though our earlier scale+pad+format pass took care of the
+    // pixel side. Force the time-domain axes too:
+    //   fps=<target>       — resample video to a constant rate
+    //   setpts=PTS-STARTPTS — re-zero PTS so concat's per-input clock
+    //                        resets cleanly
+    //   aresample=48000    — force a single audio sample rate
+    //   asetpts=PTS-STARTPTS — same for audio
+    const targetW = 1920;
     const targetH = 1080;
+    const targetFps = Math.round(seqFps) || 30;
+    const targetSampleRate = 48000;
+
     const vLabels = [];
     const aLabels = [];
     let normalize = '';
     for (let i = 0; i < concatList.length; i++) {
-      // scale=W:H force_original_aspect_ratio=decrease + pad to box keeps
+      normalize +=
-      // mixed-aspect sources inside the frame without distortion.
+        `[${i}:v:0]fps=${targetFps},` +
-      normalize += `[${i}:v:0]scale=${targetW}:${targetH}:force_original_aspect_ratio=decrease,pad=${targetW}:${targetH}:(ow-iw)/2:(oh-ih)/2,setsar=1,format=yuv420p[v${i}];`;
+        `scale=${targetW}:${targetH}:force_original_aspect_ratio=decrease,` +
+        `pad=${targetW}:${targetH}:(ow-iw)/2:(oh-ih)/2,` +
+        `setsar=1,format=yuv420p,setpts=PTS-STARTPTS[v${i}];`;
       vLabels.push(`[v${i}]`);
       if (wantAudio) {
-        // anullsrc as a fallback so missing audio doesn't blow up concat.
+        normalize +=
-        normalize += `[${i}:a:0]aresample=async=1:first_pts=0[a${i}];`;
+          `[${i}:a:0]aresample=${targetSampleRate},` +
+          `aformat=channel_layouts=stereo:sample_fmts=fltp,` +
+          `asetpts=PTS-STARTPTS[a${i}];`;
         aLabels.push(`[a${i}]`);
       }
     }
     const n = concatList.length;
     let concatExpr;
     if (wantAudio) {
-      // interleaved [v0][a0][v1][a1]…
       const interleaved = [];
       for (let i = 0; i < n; i++) { interleaved.push(vLabels[i], aLabels[i]); }
       concatExpr = `${interleaved.join('')}concat=n=${n}:v=1:a=1[outv][outa]`;