cap video resolution to save on memory

go/cmd/particleprocessorworker/main.go

@@ -240,10 +240,18 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 			tmpPath,
 		}
 	} else {
+		// Cap encoder parallelism and lookahead to keep memory bounded — screen
+		// recordings come in at native display resolution (often 1440p–4K) and
+		// libx264's per-thread lookahead/reference buffers blow past the worker's
+		// memory limit otherwise. Output is also downscaled to 1080p max, which
+		// mobile playback won't notice; the original WebM stays in GCS untouched.
 		args = []string{
 			"-y", "-i", sourceURL,
+			"-vf", "scale='min(1920,iw)':-2:flags=lanczos",
 			"-c:v", "libx264", "-preset", "veryfast", "-crf", "23",
 			"-pix_fmt", "yuv420p", "-profile:v", "baseline", "-level", "3.1",
+			"-x264-params", "rc-lookahead=20:ref=2",
+			"-threads", "2", "-filter_threads", "2",
 			"-c:a", "aac", "-b:a", "128k",
 			"-movflags", "+faststart",
 			tmpPath,