diff --git a/packages/adapters/src/media/ffmpeg.ts b/packages/adapters/src/media/ffmpeg.ts
index 72eefc1..dba7930 100644
--- a/packages/adapters/src/media/ffmpeg.ts
+++ b/packages/adapters/src/media/ffmpeg.ts
@@ -512,6 +512,9 @@ export async function renderPoster(
         "1",
         "-c:v",
         "mjpeg",
+        // JPEG uses full-range YUV; newer encoders refuse video's limited range.
+        "-pix_fmt",
+        "yuvj420p",
         "-q:v",
         "3",
         "-map_metadata",