Sound für synchrone Wiedergabe geändert

include/audiothread.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include <QThread>
+#include <QString>
+#include <atomic>
+
+#include <alsa/asoundlib.h>
+
+// Audio passthrough: captures from the grabber's ALSA device and plays it
+// straight to the default output with small buffers (low latency, so the
+// sound stays in sync with the video preview). Same implementation as in
+// the HDMI viewer.
+class AudioThread : public QThread
+{
+    Q_OBJECT
+
+public:
+    explicit AudioThread(const QString &device, QObject *parent = nullptr);
+    ~AudioThread() override;
+
+    void stop();
+
+signals:
+    void errorOccurred(const QString &message);
+
+protected:
+    void run() override;
+
+private:
+    QString           m_device;
+    std::atomic<bool> m_running{false};
+
+    // PCM parameters
+    static constexpr unsigned int      k_defaultRate     = 48000;
+    static constexpr unsigned int      k_defaultChannels = 2;
+    static constexpr snd_pcm_uframes_t k_periodFrames    = 1024;
+};

include/videowidget.h

@@ -11,6 +11,7 @@
 #include <QProcess>
 
 #include "v4l2worker.h"
+#include "audiothread.h"
 
 // A uniform, icon-only push button used for the video toolbar (start/stop,
 // freeze, screenshot, record, fullscreen, audio, ...). All toolbar buttons
@@ -142,14 +143,12 @@ private:
 
     // Audio passthrough: plays the grabber's ALSA capture device (e.g. the
     // "USB Audio" card that accompanies a /dev/videoN HDMI/USB grabber)
-    // straight to the default output, the same way the HDMI viewer does it.
-    // Implemented by shelling out to `ffplay -f alsa -i <device>` with
-    // -nodisp (audio only, no extra window) - same approach as recording,
-    // just piping the other direction (device -> speakers instead of
-    // frames -> file).
+    // straight to the default output. Uses the same native ALSA
+    // capture->playback thread (AudioThread) as the HDMI viewer, with small
+    // buffers so the sound stays in sync with the video preview.
     QComboBox   *m_audioCombo    = nullptr;
     QPushButton *m_audioBtn      = nullptr;
-    QProcess    *m_audioProcess  = nullptr;
+    AudioThread *m_audioThread   = nullptr;
     bool         m_audioActive   = false;
 
     // Fullscreen overlay window (nullptr when not open). Owns itself via