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decklinksrc: Use a more accurate capture time

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Use the hardware reference clock time when the frame was finished being captured
instead of a time much further down the road.

This improves the stability/accuracy of buffer times.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2040>
This commit is contained in:
Edward Hervey 2021-02-26 11:39:10 +01:00 committed by Edward Hervey
parent a9211a5067
commit 6fe54f7f48
1 changed files with 35 additions and 0 deletions
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35
sys/decklink/gstdecklink.cpp
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@ -1023,6 +1023,41 @@ public:
if (clock) {
capture_time = gst_clock_get_time (clock);
if (video_frame) {
// If we have the actual capture time for the frame, compensate the
// capture time accordingly.
//
// We do this by subtracting the belay between "now" in hardware
// reference clock and the time when the frame was finished being
// capture based on the same hardware reference clock.
//
// We then subtract that difference from the "now" on the gst clock.
//
// *Technically* we should be compensating that difference for the
// difference in clock rate between the "hardware reference clock" and
// the GStreamer clock. But since the values are quite small this has
// very little impact.
BMDTimeValue hardware_now;
res = m_input->input->GetHardwareReferenceClock (GST_SECOND, &hardware_now, NULL, NULL);
if (res == S_OK) {
res =
video_frame->GetHardwareReferenceTimestamp (GST_SECOND,
&hardware_time, &hardware_duration);
if (res != S_OK) {
GST_ERROR ("Failed to get hardware time: 0x%08lx", (unsigned long) res);
hardware_time = GST_CLOCK_TIME_NONE;
hardware_duration = GST_CLOCK_TIME_NONE;
} else {
GstClockTime hardware_diff = hardware_now - hardware_time;
GST_LOG ("Compensating capture time by %" GST_TIME_FORMAT,
GST_TIME_ARGS (hardware_diff));
if (capture_time > hardware_diff)
capture_time -= hardware_diff;
else
capture_time = 0;
}
}
}
if (capture_time > base_time)
capture_time -= base_time;
else