title: How to add a Poster Frame to an MP4 video by timecode?
body: <p>The <code>mvhd</code> atom or box of the original Quicktime MOV format supports a <code>poster time</code> variable for a timecode to use as a poster frame that can be used in preview scenarios as a thumbnail image or cover picture. As far as I can tell, the ISOBMFF-based MP4 format (.m4v) has inherited this feature, but I cannot find a way to set it using <a href="http://ffmpeg.org/documentation.html" rel="nofollow noreferrer">FFmpeg</a> or <a href="https://github.com/gpac/gpac/releases" rel="nofollow noreferrer">MP4box</a> or similar cross-platform CLI software. <strong>Edit:</strong> Actually, neither ISOBMFF nor MP4 imports this feature from MOV. Is there any other way to achieve this, e.g. using something like HEIFʼs derived images with a <code>thmb</code> (see <a href="https://standards.iso.org/ittf/PubliclyAvailableStandards/c071851_ISO_IEC_14496-12_2015_Amd_2_2018.zip" rel="nofollow noreferrer" title="zipped PDF of ISO/IEC 14496-12:2015 Amd. 2:2018">Amendment 2</a>) role? </p>
  
  <p><a href="https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html#//apple_ref/doc/uid/TP40000939-CH204-32947" rel="nofollow noreferrer" title="QuickTime File Format Specification"><img src="https://i.stack.imgur.com/Lwqpz.png" alt="&lt;code&gt;mvhd&lt;/code&gt; box layout"></a></p>
  
  <p>The original Apple Quicktime (Pro) editor did have a menu option for doing just that. (Apple <a href="https://larryjordan.com/articles/change-your-movies-poster-frame/" rel="nofollow noreferrer">Compressor</a> and <a href="https://discussions.apple.com/thread/7820966" rel="nofollow noreferrer">Photos</a> could do it, too).</p>
  
  <p><a href="https://i.stack.imgur.com/Fwu6P.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Fwu6P.png" alt="Quicktime menu"></a></p>
  
  <p>To be clear, I do <em>not</em> want to attach a separate image file, which could possibly be a screenshot grabbed from a movie still, as a separate track to the multimedia container. I know how to do <em>that</em>:</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/54717175/how-do-i-add-a-custom-thumbnail-to-a-mp4-file-using-ffmpeg">Stackoverflow #54717175</a></li>
  <li><a href="https://superuser.com/questions/597945/set-mp4-thumbnail">Superuser #597945</a></li>
  </ul>
  
  <p>I also know that some people used to copy the designated poster frame from its original position to the very first frame, but many automatically generated previews use a later time index, e.g. from 10 seconds, 30 seconds, 10% or 50% into the video stream.</p>