Reduce mixer and Bluetooth buffers from 500 ms to 200 ms

SBC medium, not the larger buffer, removed the headphone relay dropouts,
so cut dmix, bluealsa-aplay and alsaloop buffers to 200 ms and the
Shairport backend buffer to 0.15 s. Verified by listening (iPhone ->
headphones, with AirPlay mixed in) with no RTP loss or underruns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/radxa-audio.py

@@ -80,7 +80,7 @@ pcm.radxa_dmix {{
         channels 2
         period_time 0
         period_size {rate // 100}
-        buffer_size {rate // 2}
+        buffer_size {rate // 5}
     }}
     bindings {{ 0 0 1 1 }}
 }}
@@ -105,7 +105,7 @@ def templates(c):
     name = {json.dumps(c['name'], ensure_ascii=False)};
     service_type = "airplay2";
     output_backend = "alsa";
-    audio_backend_buffer_desired_length_in_seconds = 0.5;
+    audio_backend_buffer_desired_length_in_seconds = 0.15;
 }};
 alsa = {{
     output_device = "radxa_mix";
@@ -126,7 +126,7 @@ Group=audio
 PrivateUsers=false
 RemoveIPC=false
 ExecStart=
-ExecStart=/usr/bin/bluealsa-aplay -S --pcm=radxa_mix --volume=software --pcm-period-time=10000 --pcm-buffer-time=500000
+ExecStart=/usr/bin/bluealsa-aplay -S --pcm=radxa_mix --volume=software --pcm-period-time=10000 --pcm-buffer-time=200000
 ''',
         '/etc/modules-load.d/radxa-audio-loopback.conf': 'snd-aloop\n',
         '/etc/modprobe.d/radxa-audio-loopback.conf': 'options snd-aloop pcm_substreams=1\n',
@@ -143,7 +143,7 @@ StartLimitIntervalSec=0
 User=shairport-sync
 Group=audio
 ExecStartPre=-/usr/bin/bluetoothctl --timeout 8 connect {addr} a2dp-sink
-ExecStart=/usr/bin/alsaloop -C hw:Loopback,1,0 -P bluealsa:DEV={addr},PROFILE=a2dp -c 2 -r 48000 -f S16_LE -t 500000 -S 4 -A 2
+ExecStart=/usr/bin/alsaloop -C hw:Loopback,1,0 -P bluealsa:DEV={addr},PROFILE=a2dp -c 2 -r 48000 -f S16_LE -t 200000 -S 4 -A 2
 Restart=always
 RestartSec=5
 TimeoutStartSec=30