bluealsa-aplay manual page extra detail

The time drift caused by rounding errors in the ALSA rate plugin
has led to a number of issues being raised by users. This change
introduces a hint on how to avoid these rounding errors by
carefully choosing the ALSA PCM period time.

doc/bluealsa-aplay.1.rst

@@ -64,7 +64,9 @@ OPTIONS
 
 --pcm-buffer-time=INT
     Set the playback PCM buffer duration time to *INT* microseconds.
-    The default is 500000.
+    The default is 500000. It is recommended to choose a buffer time that is
+    an exact multiple of the period time to avoid potential issues with some
+    ALSA plugins (see --pcm-period-time option below).
     ALSA may choose the nearest available alternative if the requested value is
     not supported.
 
@@ -83,7 +85,12 @@ OPTIONS
     period sizes. This can result in stream underruns (if the effective rate is
     too fast) or dropped A2DP frames in the **bluealsa(8)** server (if the
     effective rate is too slow). Increase the period time with this option if
-    this problem occurs.
+    this problem occurs. This effect is avoided if the selected period time
+    results in an exact number of frames at both sample rates. For example, in
+    the case of bluetooth stream sampled at 48000Hz playing to a hardware
+    device that supports only 44100Hz, choosing a period time that is a
+    multiple of 10000 microseconds will result in zero rounding error.
+    (10000 µs @ 48000Hz is 480 frames, and @ 44100Hz is 441 frames).
 
 -M NAME, --mixer=NAME
     Select ALSA mixer device to use for controlling audio output mute state