Alastor,
onchange не ставить в тег
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<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' >
<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>
<script>
window.addEventListener("DOMContentLoaded", function() {
var d = document.querySelector("#cplayer1"),
a = d.querySelector("select"),
f = d.querySelector("#film_cinemas");
a.addEventListener("change", function() {
f.src = a.value;
localStorage.setItem("rem", a.value)
});
var e = localStorage.getItem("rem");
e && (a.value = e);
e = new Event("change");
a.dispatchEvent(e);
d.addEventListener("click", function(c) {
c = c.target;
var b = a.selectedIndex;
if (c.classList.contains("previous")) b--;
else if (c.classList.contains("next")) b++;
else return;
0 > b && (b = a.options.length - 1);
b %= a.options.length;
a.selectedIndex = b;
a.dispatchEvent(e)
})
});
</script>
</body>
</html>