[Qemu-devel] [PATCH V4 2/3] audio/paaudio: prolong and make latency configurable

[Martin Schrodt]

The latency of a connection to the PulseAudio server is determined by
the tlength parameter. This was hardcoded to 10ms, which is a bit too
tight on my machine, causing audio on host and guest to malfunction.
A setting of 15ms works fine here. To allow tweaking, I also made the
setting configurable via the new -audiodev config. This allows to squeeze out 
better timings in scenarios where the emulation allows it.

I also removed setting of the minreq parameter to (seemingly arbitrary) half 
the latency, since it showed worse audio quality during my tests. Allowing 
PulseAudio to request smaller chunks helped.

Signed-off-by: Martin Schrodt <address@hidden>
---
 audio/paaudio.c | 12 ++++++------
 qapi/audio.json |  6 +++++-
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/audio/paaudio.c b/audio/paaudio.c
index ab2a37bbdb..be27c73f09 100644
--- a/audio/paaudio.c
+++ b/audio/paaudio.c
@@ -549,12 +549,8 @@ static int qpa_init_out(HWVoiceOut *hw, struct audsettings 
*as,
     ss.channels = as->nchannels;
     ss.rate = as->freq;
 
-    /*
-     * qemu audio tick runs at 100 Hz (by default), so processing
-     * data chunks worth 10 ms of sound should be a good fit.
-     */
-    ba.tlength = pa_usec_to_bytes (10 * 1000, &ss);
-    ba.minreq = pa_usec_to_bytes (5 * 1000, &ss);
+    ba.tlength = pa_usec_to_bytes(ppdo->latency, &ss);
+    ba.minreq = -1;
     ba.maxlength = -1;
     ba.prebuf = -1;
 
@@ -818,6 +814,10 @@ static int qpa_validate_per_direction_opts(Audiodev *dev,
         pdo->has_buffer_length = true;
         pdo->buffer_length = 46440;
     }
+    if (!pdo->has_latency) {
+        pdo->has_latency = true;
+        pdo->latency = 15000;
+    }
     return 1;
 }
 
diff --git a/qapi/audio.json b/qapi/audio.json
index 97aee37288..9fefdf5186 100644
--- a/qapi/audio.json
+++ b/qapi/audio.json
@@ -206,12 +206,16 @@
 #
 # @name: name of the sink/source to use
 #
+# @latency: latency you want PulseAudio to achieve in microseconds
+#           (default 15000)
+#
 # Since: 4.0
 ##
 { 'struct': 'AudiodevPaPerDirectionOptions',
   'base': 'AudiodevPerDirectionOptions',
   'data': {
-    '*name': 'str' } }
+    '*name': 'str',
+    '*latency': 'uint32' } }
 
 ##
 # @AudiodevPaOptions:
-- 
2.21.0