Remove lines in video

Nothing to do with WordPress, but the line is applied via CSS on .qt-caption::after

In your scss file, _typography.scss look for:

.qt-caption {
    padding: 0.33em 0 0.7em 0;
    margin: 0 0 0.5em 0;
    position: relative;
    &::after {
        display: block;
        position: absolute;
        width: 100%;
        height: 2px;
        content: " ";
        background: rgba(150,150,150,0.3);
        bottom: 0;
    }
}

And either remove the ::after block, or set it to display: none; instead.