gstreamer: Document various caps for the reference timestamp meta

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2132>

diff --git a/subprojects/gstreamer/gst/gstbuffer.h b/subprojects/gstreamer/gst/gstbuffer.h
index 9e487b7..12ad5f2 100644 (file)
--- a/subprojects/gstreamer/gst/gstbuffer.h
+++ b/subprojects/gstreamer/gst/gstbuffer.h
@@ -750,10 +750,18 @@ typedef struct _GstReferenceTimestampMeta GstReferenceTimestampMeta;
  * captured.
  *
  * The reference is stored as a #GstCaps in @reference. Examples of valid
- * references would be `timestamp/x-drivername-stream` for timestamps that are locally
- * generated by some driver named `drivername` when generating the stream,
- * e.g. based on a frame counter, or `timestamp/x-ntp, host=pool.ntp.org,
- * port=123` for timestamps based on a specific NTP server.
+ * references would be
+ *
+ *  * `timestamp/x-drivername-stream`: for timestamps that are locally
+ *    generated by some driver named `drivername` when generating the stream,
+ *    e.g. based on a frame counter
+ *  * `timestamp/x-ntp, host=pool.ntp.org, port=123`: for timestamps based on a
+ *    specific NTP server. Note that the host/port parameters might not always
+ *    be given.
+ *  * `timestamp/x-ptp, version=IEEE1588-2008, domain=1`: for timestamps based
+ *    on a given PTP clock.
+ *  * `timestamp/x-unix`: for timestamps based on the UNIX epoch according to
+ *    the local clock.
  *
  * Since: 1.14
  */