Improve audio compensation thresholds

Use different thresholds for enabling and disabling compensation.

Concretely, enable compensation if the difference between the average
and the target buffering levels exceeds 4 ms (instead of 1 ms). This
avoids unnecessary compensation due to small noise in buffering level
estimation.

But keep a smaller threshold (1 ms) for disabling compensation, so that
the buffering level is restored closer to the target value. This avoids
to keep the actual level close to the compensation threshold.

PR #4572 <https://github.com/Genymobile/scrcpy/pull/4572>

app/src/audio_player.c

@@ -281,8 +281,15 @@ sc_audio_player_frame_sink_push(struct sc_frame_sink *sink,
 
             float avg = sc_average_get(&ap->avg_buffering);
             int diff = ap->target_buffering - avg;
-            if (abs(diff) < (int) ap->sample_rate / 1000) {
-                // Do not compensate for less than 1ms, the error is just noise
+
+            // Enable compensation when the difference exceeds +/- 4ms.
+            // Disable compensation when the difference is lower than +/- 1ms.
+            int threshold = ap->compensation != 0
+                          ? ap->sample_rate     / 1000  /* 1ms */
+                          : ap->sample_rate * 4 / 1000; /* 4ms */
+
+            if (abs(diff) < threshold) {
+                // Do not compensate for small values, the error is just noise
                 diff = 0;
             } else if (diff < 0 && can_read < ap->target_buffering) {
                 // Do not accelerate if the instant buffering level is below