This works too - 

Qualtrics.SurveyEngine.addOnReady(function() {
    var qobj = this;
    qobj.hideNextButton(); // Hide the Next button initially

    // Get the video element
    var video = document.getElementById('myVideo');

    // Variable to track whether the video was played completely
    var videoPlayedToEnd = false;

    // Disable video controls
    video.controls = false;

    // Enable autoplay
    video.autoplay = true;

    // Add event listeners to handle video events
    video.addEventListener('ended', function() {
        // When the video ends, set the flag to true
        videoPlayedToEnd = true;
        // Show the Next button if the video was played properly
        if (videoPlayedToEnd) {
            qobj.showNextButton();
        }
    }, false);

    // Check if autoplay is supported by the browser
    var autoplaySupported = video.autoplay === true || video.hasOwnProperty('playsInline');

    // If autoplay is not supported, show a warning
    if (!autoplaySupported) {
        console.warn('Autoplay is not supported in this browser. Please click the play button to start the video.');
    }
});