Absolute time stamping and accuracy

[Josh Doe]

I'm interested in very accurately timestamping video frames such that
videos captured from different computers can be synchronously played
back. Each computer would have a highly accurate hardware clock source
(GPS-synchronized PCI card), and the file format would provide for
storing at least millisecond absolute date/times (e.g. MXF). The
framegrabbers callback at the beginning of exposure, and then I'd grab
the time from the GPS time card.

It seems I'd want to subclass GstClock to provide a method for
retrieving absolute date/time as well as clock time (i.e.
GstDateTimeClock), and then implement that class for any of the timing
cards I'd have. But from here I don't think there is a standard way to
get that information to the muxing element.

What's the best way to handle this? GST_TAG_DATE_TIME only provides
for second accuracy, so I'd either need to create a new tag and make
sure the clock time is an offset from that value, or I'd need to send
the info along with the buffer.

Thanks for any ideas,
-Josh