To set the max-width of AllVideos video output ( a bit of a hack but works for me)

• i downloaded latest version v4.8.0 from github
• the iframe does not alter anything
• the video size is controlled by the wrapping <div>s in particular "avPlayerContainer"
• the output template is allvideos-master/plugin/jw_allvideos/tmpl/Responsive/default.php
• in the responsive template I changed

  <div class="avPlayerContainer">

  to

  <div class="avPlayerContainer" style="max-width:<?php echo $output->playerWidth; ?>px;">

This is an example of the new code in action

<div class="avPlayerWrapper avVideo">
    <div class="avPlayerContainer" style="max-width:600px;">
        <div id="AVPlayerID_0_80667a8ddd8d0d2ed351d74c3990d3c1" class="avPlayerBlock">
            <iframe src="https://www.youtube.com/embed/DVbDgMh5lj4?rel=0&amp;fs=1&amp;wmode=transparent&amp;autoplay=1" allowfullscreen="" title="JoomlaWorks AllVideos Player" width="600" height="450" frameborder="0"></iframe>
        </div>
    </div>
</div>
<!-- JoomlaWorks "AllVideos" Plugin (v4.8.0) ends here-->