Put ID to source tag
<video id="myVideo" width="640" height="360">
<source id="VdoSrc" src="love.mp4" type="video/mp4">
</source></video>
You can get through javascript
var mp4Vid = document.getElementById('VdoSrc');
$(mp4Vid).attr('src', "/pathTo/love.mp4");
For more info check this
Link