PulseAudio: Fix tlength setting of QPulseAudioSink

With PA_STREAM_ADJUST_LATENCY set, PulseAudio will use the requested
tlength value to configure playback buffer size + overall sink latency.
The configured stream has a tlength of actual buffer size, which was
then used as the requested tlenght on subsequent playback streams. This
lead to buffer size getting smaller after multiple restarts, and leading
to underflows and "static" glitches caused by skipped samples.

This patch changes the requested tlength attribute to always be either
the buffer size set by the user, or the default buffer size if no buffer
size is set.

Fixes: QTBUG-116519
Pick-to: 6.7 6.6 6.5
Change-Id: Ib9ad0dc72ad7f70f172b3cc484672c9f426bde06
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>

2 files changed, 23 insertions, 11 deletions

diff --git a/src/multimedia/pulseaudio/qpulseaudiosink.cpp b/src/multimedia/pulseaudio/qpulseaudiosink.cpp
index 39d21b560..ff526e1b1 100644
--- a/src/multimedia/pulseaudio/qpulseaudiosink.cpp
+++ b/src/multimedia/pulseaudio/qpulseaudiosink.cpp
@@ -303,8 +303,9 @@ bool QPulseAudioSink::open()
 
     pa_buffer_attr requestedBuffer;
     // Request a target buffer size
-    auto targetBufferSize = bufferSize();
-    requestedBuffer.tlength = targetBufferSize ? targetBufferSize : static_cast<uint32_t>(-1);
+    auto targetBufferSize = m_userBufferSize ? *m_userBufferSize : defaultBufferSize();
+    requestedBuffer.tlength =
+            targetBufferSize ? static_cast<uint32_t>(targetBufferSize) : static_cast<uint32_t>(-1);
     // Rest should be determined by PulseAudio
     requestedBuffer.fragsize = static_cast<uint32_t>(-1);
     requestedBuffer.maxlength = static_cast<uint32_t>(-1);
@@ -537,7 +538,7 @@ qsizetype QPulseAudioSink::bytesFree() const
 
 void QPulseAudioSink::setBufferSize(qsizetype value)
 {
-    m_bufferSize = value;
+    m_userBufferSize = value;
 }
 
 qsizetype QPulseAudioSink::bufferSize() const
@@ -545,14 +546,10 @@ qsizetype QPulseAudioSink::bufferSize() const
     if (m_bufferSize)
         return m_bufferSize;
 
-    if (m_spec.rate > 0)
-        return pa_usec_to_bytes(DefaultBufferLengthMs * 1000, &m_spec);
+    if (m_userBufferSize)
+        return *m_userBufferSize;
 
-    auto spec = QPulseAudioInternal::audioFormatToSampleSpec(m_format);
-    if (pa_sample_spec_valid(&spec))
-        return pa_usec_to_bytes(DefaultBufferLengthMs * 1000, &spec);
-
-    return 0;
+    return defaultBufferSize();
 }
 
 static qint64 operator-(timeval t1, timeval t2)
@@ -732,6 +729,18 @@ PAOperationUPtr QPulseAudioSink::exchangeDrainOperation(pa_operation *newOperati
     return PAOperationUPtr(m_drainOperation.exchange(newOperation));
 }
 
+qsizetype QPulseAudioSink::defaultBufferSize() const
+{
+    if (m_spec.rate > 0)
+        return pa_usec_to_bytes(DefaultBufferLengthMs * 1000, &m_spec);
+
+    auto spec = QPulseAudioInternal::audioFormatToSampleSpec(m_format);
+    if (pa_sample_spec_valid(&spec))
+        return pa_usec_to_bytes(DefaultBufferLengthMs * 1000, &spec);
+
+    return 0;
+}
+
 QT_END_NAMESPACE
 
 #include "moc_qpulseaudiosink_p.cpp"
diff --git a/src/multimedia/pulseaudio/qpulseaudiosink_p.h b/src/multimedia/pulseaudio/qpulseaudiosink_p.h
index d7c320f7c..cf0b181ec 100644
--- a/src/multimedia/pulseaudio/qpulseaudiosink_p.h
+++ b/src/multimedia/pulseaudio/qpulseaudiosink_p.h
@@ -80,6 +80,8 @@ private Q_SLOTS:
     PAOperationUPtr exchangeDrainOperation(pa_operation *newOperation);
 
 private:
+    qsizetype defaultBufferSize() const;
+
     pa_sample_spec m_spec = {};
     // calculate timing manually, as pulseaudio doesn't give us good enough data
     mutable timeval lastTimingInfo = {};
@@ -102,8 +104,9 @@ private:
     qreal m_volume = 1.0;
 
     std::atomic<pa_operation *> m_drainOperation = nullptr;
+    qsizetype m_bufferSize = 0;
+    std::optional<qsizetype> m_userBufferSize = std::nullopt;
     int m_pullingPeriodSize = 0;
-    int m_bufferSize = 0;
     int m_pullingPeriodTime = 0;
     bool m_pullMode = true;
     bool m_opened = false;