If-statement with changing url

What is wrong with this function? The first if-statement does work. But the else-statement doesn't work.

function func() {
    if (document.getElementById("pic2").src = "pause.png") {
        document.getElementById("pic2").src = "play.png";
    } else {
        document.getElementById("pic2").src == "pause.png";
    }
}

HTML:

<div id="all" onclick="func()" onmouseover="func3()">
            <div id="background" onclick="func()" onmouseout="func2()"></div>
            <div id="pic">
                <img id="pic2" src="pause.png">
            </div>
            <video>
                <source src="test.mp4" type="video/mp4">
            </video>
        </div>