The delay buffer clock estimates the clock offset between the PTS and
the frame decoded date using an "Exponentially Weighted Moving Average"
(EWMA).
But for the first frames, the clock have less than SC_CLOCK_RANGE
points to average. Since the timing for the first frames are typically
the worst ones, give more weight to the last point for the estimation.
Once SC_CLOCK_RANGE points are available (i.e. when SC_CLOCK_RANGE ==
clock->range), the new estimation is equivalent to the previous version.
The slope encodes the drift between the device clock and the computer
clock. Its real value is expected very close to 1.
To estimate it, just assume it is exactly 1.
Since the clock is used to estimate very close points in the future, the
error caused by clock drift is totally negligible, and in practice it is
way lower than the slope estimation error.
Therefore, only estimate the offset.
The first frames are typically received and decoded with more delay than
the others, causing a wrong slope estimation on start.
To compensate, assume an initial slope of 1, then progressively use the
estimated slope.
To minimize latency (at the cost of jitter), scrcpy always displays a
frame as soon as it available, without waiting.
However, when recording (--record), it still writes the captured
timestamps to the output file, so that the recorded file can be played
correctly without jitter.
Some real-time use cases might benefit from adding a small latency to
compensate for jitter too. For example, few tens of seconds of latency
for live-streaming are not important, but jitter is noticeable.
Therefore, implement a buffering mechanism (disabled by default) to add
a configurable latency delay.
PR #2417 <https://github.com/Genymobile/scrcpy/issues/2417>
