LimeSurvey version: LimeSurvey Cloud ,  Version 5.6.29
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I've been trying to embed a youtube Video in my survey (starting from a specific timepoint and not from the beginning). I tried it in multiple ways, with the source code, as well as with the button in the user interface to embed a Video. 
For the source code I used the following code: 

<iframe width="760" height="415" src=" www.youtube.com/embed/Ko0pUIenk8Q?start=129 " title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen>

The only thing that happens then is that I get a problem record when I look into the question-preview: An error has occurred. Watch this video on Youtube.com or enable JavaScript if it is disabled in your browser. 

I checked, JavaScript is enabled in my browser. 
When I try to embed it with the user interface (just via the Youtube-Link: youtu.be/Ko0pUIenk8Q?t=129 ) it works, that the Video is embedded, but it starts from the beginning and not from minute 1:29 how it's supposed to be. 

Does anybody know what the problem could be or has had the same problem already? 

I made my video clips work by surrounding the iframe with a <div class="videodetector">...</div>

When using the 'embed Youtube clip' dialog I found that Limesurvey 6.6.6 created the <div> but not the <iframe> so I had to add that manually.

i.e.,
<div class="videodetector"><iframe frameborder="0" sandbox="allow-scripts allow-same-origin" src=" www.youtube.com/embed/xxxxxxxx?autohide=...ols=1&showinfo=0 ">