Set default volume for PeepSo video

add_filter('peepso_videos_attach_before', function ($video) {
    if (isset($video['content'])) {
        $video['content'] = preg_replace(
            '/<video([^>]*)>/',
            '<video$1 onloadstart="this.volume=0.5">',
            $video['content']
        );
    }
    return $video;
}, 999);