тогда как то так
<div class="notebook2">
<input type="radio" name="notebook2a" id="notebook2a_1" checked="checked">
<input type="radio" name="notebook2a" id="notebook2a_2">
<label name="button2" class="button2" onclick="closeModal()">
<img src="full/iconX.png" onclick="document.getElementById('videoplay').pause()">
</label>
<div id="video" onclick="document.getElementById('videoplay').play()">
<label for="notebook2a_1" style="margin-top:7px;">Video</label>
<video class="videocontent" id="videoplay" src="full/ps.mp4" poster="full/poster.png" controls preload ></video>
</div>
<div id="slides" onclick="document.getElementById('videoplay').pause()">
<label for="notebook2a_2" style="margin-top:6px;">Gallery</label>
<div class="container">
<ul id="slides">
<li class="slide showing"><img src="full/1.png"></li>
<li class="slide"><img src="full/2.png"></li>
<li class="slide"><img src="full/3.png"></li>
<li class="slide"><img src="full/4.png"></li>
</ul>
<div class="controls" id="previous">
<img src="full/left_arrow.png"/>
</div>
<div class="controls" id="next" style="left:50px;float:right">
<img src="full/right_arrow.png"/>
</div>
</div>
<ul class="thumbs">
<li class="img1"><img src="Thumbs/1.png" class="mini active" data-full-url="full/1.png"
onmouseover="this.src='thumbs/1_over.png'"
onmouseout="this.src='thumbs/1.png'"/></li>
<li class="img2"><img src="Thumbs/2.png" class="mini" data-full-url="full/2.png"
onmouseover="this.src='thumbs/2_over.png'"
onmouseout="this.src='thumbs/2.png'"/></li>
<li class="img3"><img src="Thumbs/3.png" class="mini" data-full-url="full/3.png"
onmouseover="this.src='thumbs/3_over.png'"
onmouseout="this.src='thumbs/3.png'"/></li>
<li class="img4"><img src="Thumbs/4.png" class="mini" data-full-url="full/4.png"
onmouseover="this.src='thumbs/4_over.png'"
onmouseout="this.src='thumbs/4.png'"/></li>
</ul>
</div>
<script>
document.querySelector('#videoplay').addEventListener('ended', function () {
document.querySelector('#notebook2a_2').checked = true;
}, false);
</script>