audio: master-clock playback timing, output clock compensation, buffer config, interpolated speed

- playback timer uses the audio output device as its master clock: the
  PortAudio callback counts consumed frames (including underrun
  zero-fill) so video cannot drift away from what is heard; wall clock
  remains as fallback when no clocked output is running
- output clock compensates for device output latency; new Preferences >
  Audio buffer size setting (0 = auto)
- SampleBuffer::speed() now uses linear interpolation instead of
  nearest-neighbor sampling
- regression tests: audio-clock driven timer (fwd/rev/speed), wall
  clock fallback, interpolation correctness

app/dialog/preferences/tabs/preferencesaudiotab.cpp

@@ -124,6 +124,20 @@ PreferencesAudioTab::PreferencesAudioTab()
 						.toStdString()));
 				output_param_layout->addWidget(output_fmt_combo_, output_row,
 											   1);
+
+				output_row++;
+
+				output_param_layout->addWidget(
+					new QLabel(tr("Buffer Size:")), output_row, 0);
+
+				output_buffer_size_ = new QSpinBox();
+				output_buffer_size_->setRange(0, 65536);
+				output_buffer_size_->setSpecialValueText(tr("Auto"));
+				output_buffer_size_->setSuffix(tr(" frames"));
+				output_buffer_size_->setValue(
+					OAK_CONFIG("AudioOutputBufferSize").toInt());
+				output_param_layout->addWidget(output_buffer_size_, output_row,
+											   1);
 			}
 		}
 
@@ -222,6 +236,7 @@ void PreferencesAudioTab::accept(MultiUndoCommand *command)
 		QVariant::fromValue(output_ch_layout_combo_->get_channel_layout());
 	OAK_CONFIG("AudioOutputSampleFormat") = QString::fromStdString(
 		output_fmt_combo_->get_sample_format().to_string());
+	OAK_CONFIG("AudioOutputBufferSize") = output_buffer_size_->value();
 
 	OAK_CONFIG("AudioRecordingFormat") = record_format_combo_->get_format();
 	OAK_CONFIG("AudioRecordingCodec") = record_options_->get_codec();

app/dialog/preferences/tabs/preferencesaudiotab.h

@@ -25,6 +25,7 @@
 #include <QComboBox>
 #include <QPushButton>
 #include <QCheckBox>
+#include <QSpinBox>
 
 #include "dialog/configbase/configdialogbase.h"
 #include "dialog/export/exportaudiotab.h"
@@ -68,6 +69,11 @@ private:
 	ChannelLayoutComboBox *output_ch_layout_combo_;
 	SampleFormatComboBox *output_fmt_combo_;
 
+	/**
+   * @brief UI widget for the output buffer size in frames (0 = auto)
+   */
+	QSpinBox *output_buffer_size_;
+
 	ExportFormatComboBox *record_format_combo_;
 
 	ExportAudioTab *record_options_;