? caps for gst_buffer_add_reference_timestamp_meta

[Philippe De Muyter]

On Mon, Feb 01, 2021 at 04:30:14PM +0200, Sebastian Dröge wrote:
> On Mon, 2021-02-01 at 15:23 +0100, Philippe De Muyter wrote:
> > 
> > I recently discovered the new methods
> > gst_buffer_add_reference_timestamp_meta
> > and gst_buffer_get_reference_timestamp_meta you added to gstreamer.
> > 
> > As I don't find examples of their usage, could you tell me what you
> > would use as caps for a UTC timestamp provided by the v4l2 driver ?
> 
> The Decklink and AJA plugins use "timestamp/x-decklink-stream" and
> similar.
> 
> I think in your case for UTC it would make sense to use "timestamp/x-
> v4l2-utc" or so?
> 
> What does UTC mean here though?

It means that the v4l2 buffers are timestamped in the hardware (actually by
a real-time CPU) using a UTC clock (the linux 'realtime' clock, no matter
how itself is synchronized : ntp, gps, ptp or something else)

Of course it implies also that the timestamp_flags field of v4l2 buffers
is able to tell that to the user, e.g. using a new V4L2_BUF_FLAG_TIMESTAMP_UTC
value instead of V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC for
V4L2_BUF_FLAG_TIMESTAMP_MASK.

Philippe