fps limiter option, now default to 60

uses -fpsmax on ffmpeg

pack-vid

@@ -15,7 +15,8 @@ $options = [
     'letterbox' => false,
     'audio' => false,
     'exposure' => '0',
-    'peak' => '10000'
+    'peak' => '10000',
+    'fps' => '60',
 ];
 
 while ( count( $args ) > 0 && substr( $args[0], 0, 2 ) == '--' ) {
@@ -36,7 +37,8 @@ if ( count ( $args ) < 2 ) {
         "  --letterbox    pad instead of cropping\n" .
         "  --audio        include audio\n" .
         "  --exposure=n   adjust exposure\n" .
-        "  --peak=n       set HDR peak nits\n"
+        "  --peak=n       set HDR peak nits\n" .
+        "  --fps=n        set frame rate\n"
     );
 }
 [ $src, $dest ] = $args;
@@ -183,14 +185,14 @@ function convert( $src, $dest, $options ) {
     }
     $vf = implode( ',', $filters );
 
-    $fps = 30;
+    $fps = $options['fps'];
 
     $passlog = tempnam( '.', 'pack-vid-passlog' );
     run( 'ffmpeg',
         array_merge( [
             '-i', $src,
             '-f', 'mp4',
-            '-r', $fps,
+            '-fpsmax', $fps,
             '-vf', $vf,
             '-c:v', 'libx264',
             '-b:v', $bitrate,
@@ -206,7 +208,7 @@ function convert( $src, $dest, $options ) {
         array_merge( [
             '-i', $src,
             '-vf', $vf,
-            '-r', $fps,
+            '-fpsmax', $fps,
             '-c:v', 'libx264',
             '-b:v', $bitrate,
             '-preset', 'veryslow',