Since variables are not compatible with {% %}
calls, I ended up reproducing much of the plugin's functionality in this one line. I started with the BetterTube and modified it for my needs.
{% if post.video %}
{% capture video_id %}{{ post.video |
replace: 'https://www.youtube.com/watch?v=','' |
replace: 'https://youtu.be/', '' }}{% endcapture %}
<figure class='BetterTube' data-youtube-id='{{video_id}}' data-player-width=''
data-player-height='' id='{{video_id}}' style='padding-bottom: 56.25%'>
<a class='BetterTubePlayer' href='http://www.youtube.com/watch?v={{video_id}}'
style='background: url(http://img.youtube.com/vi/{{video_id}}/hqdefault.jpg) 50%
50% no-repeat rgb(0, 0, 0);'></a><div class='BetterTube-playBtn'></div>
</figure>
{% elsif post.image %}
<img src="{{ post.image }}" class="post-image" alt="{{ post.title }}">
{% endif %}
I wished I could simply call the plugin, but sadly I don't think it's possible.