Bug#771391: libqt5multimedia5: QAudioDeviceInfo provides no audio devices on an alsa-only system without pulseaudio

[Chris Ruvolo <cruvolo+debbugs@gmail.com>]

Package: libqt5multimedia5
Version: 5.3.2-2~bpo70+2
Severity: important

Dear Maintainers,

Thank you for the recent backport of QT5 to wheezy-backports.  I am
using this version, and running into a problem with multimedia audio.
My system has alsa devices; pulseaudio is not installed.

QT5 audio programs see no devices.  Including tools in
/usr/lib/x86_64-linux-gnu/qt5/examples/multimedia/.

To verify, I modified the main.cpp for the audioinput example to output
audio device info.  Diff follows.

I was expecting to see alsa devices, but instead
QAudioDeviceInfo::defaultInputDevice() returns a null device, and
QAudioDeviceInfo::availableDevices() returns an empty list.

libqt5multimedia5-plugins, libqt5multimediaquick-p5 and
libqt5multimediawidgets5 are also installed.

Any advice you have to debug this would be welcomed.

Thank you.
-Chris


--- /usr/lib/x86_64-linux-gnu/qt5/examples/multimedia/audioinput/main.cpp	2014-09-11 06:48:26.000000000 -0400
+++ main.cpp	2014-11-29 00:54:46.367809159 -0500
@@ -39,6 +39,9 @@
 ****************************************************************************/
 
 #include <QtWidgets>
+#include <QAudioDeviceInfo>
+#include <QAudioInput>
+#include <QTextStream>
 
 #include "audioinput.h"
 
@@ -47,6 +50,15 @@
     QApplication app(argv, args);
     app.setApplicationName("Audio Input Test");
 
+    const QAudioDeviceInfo &defaultDeviceInfo = QAudioDeviceInfo::defaultInputDevice();
+    QTextStream(stdout) << "default: " << defaultDeviceInfo.deviceName() << " isNull? " << defaultDeviceInfo.isNull() << endl;
+    foreach (const QAudioDeviceInfo &deviceInfo, QAudioDeviceInfo::availableDevices(QAudio::AudioInput)) {
+        if (deviceInfo != defaultDeviceInfo)
+			QTextStream(stdout) << "device: " << deviceInfo.deviceName() << " isNull? " << defaultDeviceInfo.isNull() << endl;
+    }
+	return 0;
+
+
     InputTest input;
     input.show();
 

Output:


$ ./audioinput
PulseAudioService: pa_context_connect() failed
default:  isNull? 1


-- System Information:
Debian Release: 7.7
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.16-0.bpo.3-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages libqt5multimedia5 depends on:
ii  libc6                            2.19-7
ii  libpulse0                        4.0-6~bpo7+1
ii  libqt5core5a [qtbase-abi-5-3-2]  5.3.2+dfsg-4~bpo70+1
ii  libqt5gui5                       5.3.2+dfsg-4~bpo70+1
ii  libqt5network5                   5.3.2+dfsg-4~bpo70+1
ii  libstdc++6                       4.9.1-19
ii  multiarch-support                2.13-38+deb7u6

libqt5multimedia5 recommends no packages.

libqt5multimedia5 suggests no packages.

-- no debconf information