Youtube links not supported in iOS

I have not heard of this issue. Have you been able to test on a local iOS device, confirming the app is up to date? Can you share the line of code and any class stylizations?

iPhone users have reported that there youtube links are not included in emails sent from marketo.

Well, the links are certainly included in the emails.  Marketo doesn't (and can't) change the outgoing email content depending on device.

Of course the image/link may not display for some reason, but I did a test just now with a standard Video element, the Mail app on iOS 9.3.5, and my old iPad, and it worked fine. So you're going to need to be more precise about documenting where/what isn't working.

Bear in mind that a Video module is not a playable video in any way. It's merely a packaged <table> element with some predictable rowspan and colspan hackery to overlay a couple of linked images, like so:

<table class="mktoModule m_video" id="videoe3fd7006-b7d3-459d-bf79-49adc77155ca" align="center" border="0" cellpadding="0" cellspacing="0" width="100%"> 
<tbody> 
<tr> 
<td valign="top" bgcolor="#ffffff"> 
<center> 
<table class="table600" width="600" align="center" border="0" cellpadding="0" cellspacing="0"> 
<tbody> 
<tr> 
<td> 
<center> 
<div class="mktoVideo" id="video2e3fd7006-b7d3-459d-bf79-49adc77155ca"> 
<table style="mso-hide:all;"> 
<tbody> 
<tr> 
<td></td> 
<td rowspan="2"> <a href="http://click.example.com/VHESp3xrPMV6G2GcPsS8oC49" target="_blank">
<img class="mktoVideoThumbnail" alt="" src="https://img.youtube.com/vi/Srmdij0CU1U/0.jpg" width="480" height="360" style="width: 480px; height: 360px; min-height: 360px; max-height: 360px;" /> </a> </td> 
</tr> 
<tr> 
<td colspan="2"> 
<center> 
<a href="http://click.example.com/VHESp3xrPMV6G2GcPsS8oC49" target="_blank">
<img class="mktoVideoPlaybutton" src="https://app-sj01.marketo.com/images/templatePicker/play-video.png" width="128" height="128" /> </a> 
</center></td> 
</tr> 
</tbody> 
</table> 
<!--[if gte mso 12]>
<a href="http://click.example.com/VHESp3xrPMV6G2GcPsS8oC49" target="_blank">
<img class='mktoVideoThumbnail' alt="" src="https://img.youtube.com/vi/Srmdij0CU1U/0.jpg" width="480" height="360"/>
</a>
<![endif]--> 
</div> 
</center> </td> 
</tr> 
</tbody> 
</table>