Cómo mostrar el primer cuadro del elemento de video en HTML

Try appending  #t={seconds} to the end of your src value. Here's an example:

<video width="300" height="150">
   <source src="testvideo.mp4#t=0.1" type="video/mp4" />
</video>

It works fine on Chrome/Firefox and many other browsers.
Mlifonza