[libcamera-devel] [PATCH v2 23/27] gst: libcamerasrc: Implement timestamp support

[Laurent Pinchart]

Hi Nicolas,

Thank you for the patch.

On Thu, Feb 27, 2020 at 03:04:03PM -0500, Nicolas Dufresne wrote:
> 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 at collabora.com>
> ---
>  src/gstreamer/gstlibcamerapad.cpp | 23 +++++++++++++++++++++++
>  src/gstreamer/gstlibcamerapad.h   |  2 ++
>  src/gstreamer/gstlibcamerasrc.cpp | 20 ++++++++++++++++++++
>  3 files changed, 45 insertions(+)
> 
> diff --git a/src/gstreamer/gstlibcamerapad.cpp b/src/gstreamer/gstlibcamerapad.cpp
> index 2cf1630..31d3edd 100644
> --- a/src/gstreamer/gstlibcamerapad.cpp
> +++ b/src/gstreamer/gstlibcamerapad.cpp
> @@ -62,9 +62,24 @@ gst_libcamera_pad_get_property(GObject *object, guint prop_id, GValue *value,
>  	}
>  }
>  
> +static gboolean
> +gst_libcamera_pad_query(GstPad *pad, GstObject *parent, GstQuery *query)
> +{
> +	auto *self = GST_LIBCAMERA_PAD(pad);
> +
> +	if (query->type != GST_QUERY_LATENCY)
> +		return gst_pad_query_default(pad, parent, query);
> +
> +	/* TRUE here means live, we assumes that max latency is the same as min
> +	 * as we have no idea that duration of frames. */

	/*
	 * ...
	 */

> +	gst_query_set_latency(query, TRUE, self->latency, self->latency);
> +	return TRUE;
> +}
> +
>  static void
>  gst_libcamera_pad_init(GstLibcameraPad *self)
>  {
> +	GST_PAD_QUERYFUNC(self) = gst_libcamera_pad_query;
>  }
>  
>  static GType
> @@ -172,3 +187,11 @@ gst_libcamera_pad_has_pending(GstPad *pad)
>  	GLibLocker lock(GST_OBJECT(self));
>  	return (self->pending_buffers.length > 0);
>  }
> +
> +void
> +gst_libcamera_pad_set_latency(GstPad *pad, GstClockTime latency)
> +{
> +	auto *self = GST_LIBCAMERA_PAD(pad);
> +	GLibLocker lock(GST_OBJECT(self));
> +	self->latency = latency;
> +}
> diff --git a/src/gstreamer/gstlibcamerapad.h b/src/gstreamer/gstlibcamerapad.h
> index eb24000..a3291e8 100644
> --- a/src/gstreamer/gstlibcamerapad.h
> +++ b/src/gstreamer/gstlibcamerapad.h
> @@ -32,4 +32,6 @@ GstFlowReturn gst_libcamera_pad_push_pending(GstPad *pad);
>  
>  bool gst_libcamera_pad_has_pending(GstPad *pad);
>  
> +void gst_libcamera_pad_set_latency(GstPad *pad, GstClockTime latency);
> +
>  #endif /* __GST_LIBCAMERA_PAD_H__ */
> diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> index 70f2048..73a1360 100644
> --- a/src/gstreamer/gstlibcamerasrc.cpp
> +++ b/src/gstreamer/gstlibcamerasrc.cpp
> @@ -151,6 +151,26 @@ GstLibcameraSrcState::requestCompleted(Request *request)
>  	for (GstPad *srcpad : this->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(this->src)) {
> +			GstClockTime gst_base_time = GST_ELEMENT(this->src)->base_time;
> +			GstClockTime gst_now = gst_clock_get_time(GST_ELEMENT_CLOCK(this->src));
> +			/* \todo Need to expose which reference clock the timestamp relates to. */

Something we need to do indeed. We're considering standardizing on
CLOCK_BOOTTIME, would that be good for gstreamer ?

> +			GstClockTime sys_now = g_get_monotonic_time() * 1000;
> +
> +			/* Deduced from: sys_now - sys_base_time == gst_now - gst_bae_time */

s/gst_bae_time/gst_base_time/

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> +			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);
>  	}
>  

-- 
Regards,

Laurent Pinchart