gst: libcamerasrc: Implement timestamp support

This is an experimental patch adding timestamp support to the libcamerasrc
element. This patch currently assume that the driver timestamp are relative to
the system monotonic clock. Without a reference clock source, the timestamp are
otherwise unusable, and without timestamp only minor use case can be achieved.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index 0b4cae79..64077f36 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -154,6 +154,26 @@ GstLibcameraSrcState::requestCompleted(Request *request)
 	for (GstPad *srcpad : srcpads_) {
 		Stream *stream = gst_libcamera_pad_get_stream(srcpad);
 		buffer = wrap->detachBuffer(stream);
+
+		FrameBuffer *fb = gst_libcamera_buffer_get_frame_buffer(buffer);
+
+		if (GST_ELEMENT_CLOCK(src_)) {
+			GstClockTime gst_base_time = GST_ELEMENT(src_)->base_time;
+			GstClockTime gst_now = gst_clock_get_time(GST_ELEMENT_CLOCK(src_));
+			/* \todo Need to expose which reference clock the timestamp relates to. */
+			GstClockTime sys_now = g_get_monotonic_time() * 1000;
+
+			/* Deduced from: sys_now - sys_base_time == gst_now - gst_base_time */
+			GstClockTime sys_base_time = sys_now - (gst_now - gst_base_time);
+			GST_BUFFER_PTS(buffer) = fb->metadata().timestamp - sys_base_time;
+			gst_libcamera_pad_set_latency(srcpad, sys_now - fb->metadata().timestamp);
+		} else {
+			GST_BUFFER_PTS(buffer) = 0;
+		}
+
+		GST_BUFFER_OFFSET(buffer) = fb->metadata().sequence;
+		GST_BUFFER_OFFSET_END(buffer) = fb->metadata().sequence;
+
 		gst_libcamera_pad_queue_buffer(srcpad, buffer);
 	}