<para>
	The date part of the GPS timestamp which corresponds to a known position
	in the video.
</para>
<para>
	Format is yyyymmdd. This option must be used together with
	<option>gps_time</option>; if one or both are missing, the timestamp of the
	first GPS trackpoint is used.
</para>
<para>
	The video position to which the timestamp corresponds can be set with the
	<option>video_time</option> option.
</para>
