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timeoverlay: Add time-line property options "clock-time" and "render-time"

Submitted by Will Manley

Link to original bug (#767105)

Description

Created attachment 328880
patch 1/3

timeoverlay: Add time-line property options "clock-time" and "render-time"

These are useful for debugging and latency measurements:

  • clock-time is the time on the GstPipeline clock.
  • render-time is the clock time at which the frame will actually be
    displayed taking into account the latency of the pipeline. This is
    relevant for live pipelines.

My use-case for this is measuring the latency of video-capture devices and
TVs. By using a GstSystemClock with a CLOCK_REALTIME clock running on
a Raspberry Pi I'm hoping to take latency measurements.

I couldn't think of a way to create an automated test for this without
introducing a bunch of unacceptable dependencies (in stb-tester we would use
OCR), so I've tested manually with the below program:

int main(int argc, char* argv[])  
{  
  GstElement * epipeline;  
  GstPipeline * pipeline;  
  GstClock* clock;  
  struct timespec ts;  
  int res;  
  
  gst_init(&argc, &argv);  
  
  epipeline = gst_parse_launch(  
      "videotestsrc is-live=true pattern=white "  
      "! video/x-raw,width=1280,height=720 "  
      "! timeoverlay time-mode=render-time "  
      "! timeoverlay deltay=30 time-mode=clock-time "  
      "! xvimagesink", NULL);  
  
  g_return_val_if_fail (epipeline != NULL, 1);  
  pipeline = GST_PIPELINE(epipeline);  
  
  gst_element_set_state(epipeline, GST_STATE_READY);  
  
  clock = g_object_new (GST_TYPE_SYSTEM_CLOCK, "clock-type",  
      GST_CLOCK_TYPE_REALTIME, NULL);  
  gst_pipeline_use_clock(pipeline, clock);  
  gst_pipeline_set_latency(pipeline, GST_SECOND);  
  
  res = clock_gettime(CLOCK_REALTIME, &ts);  
  g_return_val_if_fail (res == 0, 1);  
  
  printf("Start time: %i:%02i:%02i.%03i\n", ts.tv_sec / 60 / 60,  
      ts.tv_sec / 60 % 60, ts.tv_sec % 60, ts.tv_nsec / 1000000);  
  gst_element_set_state(epipeline, GST_STATE_PLAYING);  
  
  usleep(30*1000000);  
  gst_element_set_state(epipeline, GST_STATE_NULL);  
}

Patch 328880, "patch 1/3":
0001-basetextoverlay-Add-src_event-vmethod.patch