diff --git a/pack-vid b/pack-vid
index 17ca5d6..ce71466 100755
--- a/pack-vid
+++ b/pack-vid
@@ -130,10 +130,14 @@ function convert( $src, $dest, $options ) {
         $scaleWidth = evenize( $width * $frameHeight / $height );
     }
 
+    $peakNits = 2000;
+    $sdrNits = 80;
+    $peak = $peakNits / $sdrNits;
+
     $filters = [ "scale=w=$scaleWidth:h=$scaleHeight" ];
     if ( $hdr ) {
         $filters[] = "zscale=t=linear:p=bt709";
-        $filters[] = "tonemap=hable:peak=8";
+        $filters[] = "tonemap=hable:peak=$peak";
         $filters[] = "zscale=t=bt709:m=bt709:r=full";
     }
     $filters[] = "format=yuv420p";
@@ -147,6 +151,7 @@ function convert( $src, $dest, $options ) {
 
     $fps = 30;
 
+    $passlog = tempnam( '.', 'pack-vid-passlog' );
     run( 'ffmpeg',
         array_merge( [
             '-i', $src,
@@ -157,6 +162,7 @@ function convert( $src, $dest, $options ) {
             '-b:v', $bitrate,
             '-preset', 'veryslow',
             '-pass', '1',
+            '-passlogfile', $passlog,
             '-g', $keyframeInt,
         ], $audio, [
             '-y', '/dev/null'
@@ -171,6 +177,7 @@ function convert( $src, $dest, $options ) {
             '-b:v', $bitrate,
             '-preset', 'veryslow',
             '-pass', '2',
+            '-passlogfile', $passlog,
             '-g', $keyframeInt,
         ], $audio, [
             '-movflags', '+faststart',