<div dir="ltr"> We’re new to GStreamer and are writing our own elements. We’re trying to understand which clocks are used for jitter calculation. From the GStreamer documentation: <a href="http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-qos.txt">http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-qos.txt</a> “A buffer with timestamp B1 arrives in the sink at time T1. The buffer timestamp is then synchronized against the clock which yields a jitter J1 return value from the clock. The jitter J1 is simply calculated as J1 = CT - B1 Where CT is the clock time when the entry arrives in the sink. This value is calculated inside the clock when we perform gst_clock_entry_wait(). If the jitter is negative, the entry arrived in time and can be rendered after waiting for the clock to reach time B1 (which is also CT - J1). If the jitter is positive however, the entry arrived too late in the sink and should therefore be dropped. J1 is the amount of time the entry was late.” We assume the clock is the monotonically increasing wall clock, not the running time nor the stream time shown ins section 14.4 of the GStreamer application development manual. From the documentation the running time always starts at zero so the running time and stream time are always less than the clock time. In the GStreamer clocks diagram (and the real-world) the clock time is always greater than stream time and the running time. Given that and the equation above ( J1 = CT – B1) , jitter will always be positive. According to GStreamer documentation “If the jitter is positive however, the entry arrived too late in the sink and should therefore be dropped. “ Questions: 1. So all buffers will always be late and should be dropped?! What are we missing? 2. Which timestamp is the documentation referring to? GStreamer calls out one in the Linux version of gstbuffer.h:“ GstClockTime timestamp;” and two in the windows version: pts and gts. * @pts: presentation timestamp of the buffer, can be #GST_CLOCK_TIME_NONE when the * pts is not known or relevant. The pts contains the timestamp when the * media should be presented to the user. * @dts: decoding timestamp of the buffer, can be #GST_CLOCK_TIME_NONE when the * dts is not known or relevant. The dts contains the timestamp when the * media should be processed GstClockTime pts; GstClockTime dts; 3. Which of the three clocks (clocktime, running time, stream time) are the pts and dts referring to? 4. It seems the correct jitter formula is: Jitter = buffer_arrival_time - base_time – buffer_time_stamp Where buffer_arrival_time is read from the system clock. Thanks. </div>