// Find all YouTube videos

var $allVideos = $("iframe[src^='http://player.vimeo.com'], iframe[src^='http://www.youtube.com'], embed[src^='http://www.youtube.com']"),

    // The element that is fluid width

    $fluidEl = $("body");

// Figure out and save aspect ratio for each video

$allVideos.each(function() {

  $(this)

    .data('aspectRatio', this.height / this.width)

    // and remove the hard coded width/height

    .removeAttr('height')

    .removeAttr('width');

});

// When the window is resized

$(window).resize(function() {

  var newWidth = $fluidEl.width();

  // Resize all videos according to their own aspect ratio

  $allVideos.each(function() {

    var $el = $(this);

    $el

      .width('300')

      .height('260');

  });

// Kick off one resize to fix all videos on page load

}).resize();

이걸 모바일 게시판 스킨 js파일에 넣어주시면 됩니다

출처 : http://www.xpressengine.com/tip/20990394