вот так вроде норм
<div id="cplayer1" style="display:block;"><iframe name='film_cinemas' id='film_cinemas' src='http://vk.com/video_ext.php?oid=177595935&id=162959834&hash=71483af4bb9b25b5&hd=3' width='307' height='260' frameborder='0'></iframe>
<div class='vk_select'><button class="previous">←</button><select size='1' onchange="javascript:if(document.getElementById('film_cinemas')) document.getElementById('film_cinemas').src=this.value;">
<option value='http://vk.com/video_ext.php?oid=177595935&id=162959834&hash=71483af4bb9b25b5&hd=3'>1 серия</option><option value="http://vk.com/video_ext.php?oid=177595935&id=162959836&hash=b095322a1122a202&hd=3">2 серия</option><option value="http://vk.com/video_ext.php?oid=177595935&id=162959838&hash=947cc72f8178eb3a&hd=3">3 серия</option><option value="http://vk.com/video_ext.php?oid=177595935&id=162959840&hash=c00fa8b2df9ead45&hd=3">4 серия</option>
</select>
<button class="next">→</button>
</div></div>
<form name="test" method="post">
<b>быстрый переход</b>
<input type="text" size="1" maxlength=3 pattern="\d*" name="num">
<input type="submit" value="ОК">
</form>
<script>
window.addEventListener("DOMContentLoaded", function() {
var d = document.querySelector("#cplayer1"),
s = d.querySelector("select");
d.addEventListener("click", function(b) {
var a = b.target, i = s.selectedIndex;
if(a.classList.contains("previous")) i-- ;
else if(a.classList.contains("next")) i++ ;
else return;
if(i < 0) i = s.options.length - 1;
i %= s.options.length;
s.selectedIndex = i;
s.onchange()
})
var form = document.test;
form.onsubmit = function() {
var i = (this.num.value - 1)||0 ;
if(i < 0) i = 0;
if(i > s.options.length - 1) i = s.options.length - 1;
s.selectedIndex = i ;
this.num.value = ++i;
s.onchange();
return false;
}
});
</script>