QAudioDecoder

snapcraft
1

Hi,

I’m trying to use QAudioDecoder in a snap, I get “Playbin element is not valid” error. See source of qgstreameraudiodecodersession.cpp

The only thing in the syslog corresponding to this is:
kernel: [ 7832.904965] audit: type=1326 audit(1625711895.215:281): auid=1000 uid=1000 gid=1000 ses=4 subj=snap.amp-waver.waver pid=9014 comm="decoder" exe="/snap/amp-waver/x1/opt/waver/bin/waver" sig=0 arch=c000003e syscall=314 compat=0 ip=0x7f496189489d code=0x50000

confinement: strict
base: core20
audio-playback plug is connected and works
The app compiles without a problem.

In an attempt to resolve the problem, I added all the gstreamer and codec packages I could think of to stage-packages:
- freeglut3
- gir1.2-gst-plugins-base-1.0
- gir1.2-gstreamer-1.0
- gstreamer1.0-alsa
- gstreamer1.0-clutter-3.0
- gstreamer1.0-gl
- gstreamer1.0-gtk3
- gstreamer1.0-libav
- gstreamer1.0-packagekit
- gstreamer1.0-vaapi
- gstreamer1.0-x
- gstreamer1.0-pulseaudio
- gstreamer1.0-plugins-base
- gstreamer1.0-plugins-good
- gstreamer1.0-plugins-bad
- gstreamer1.0-plugins-ugly
- libqt5core5a
- libqt5dbus5
- libqt5gui5
- libqt5keychain1
- libqt5multimedia5
- libqt5multimedia5-plugins
- libqt5multimediagsttools5
- libqt5network5
- libqt5qml5
- libqt5quick5
- libqt5quick5-gles
- libqt5quickcontrols2-5
- libqt5sql5-sqlite
- libqt5xml5
- libavcodec58
- libavcodec-extra
- libavcodec-extra58
- libavdevice58
- libavfilter7
- libavformat58
- libavresample4
- libavutil56
- libcodec2-0.9
- libpostproc55
- libswresample3
- libswscale5
- libglu1-mesa
- libgstreamer1.0-0
- libgstreamer-gl1.0-0
- libgstreamer-plugins-base1.0-0
- libgstreamer-plugins-bad1.0-0
- libgstreamer-plugins-good1.0-0
- libpulse0
- libssh2-1
- libtag1v5
- qml-module-qtquick2
- qml-module-qtquick-controls2
- qml-module-qtquick-layouts
- qml-module-qtquick-window2
- qt5-image-formats-plugins
But to no avail.

The app works in classic confinement.

Any help would be greatly appreciated.

2

have you tried installing the snappy-debug snap and running the snappy-debug command in a second terminal while running your app ? that might give some suggestions about the denials …

3

Thanks for the suggestion. snappy-debug recommended to add the process-control plug, which I did, and connected it manually. Unfortunately, the error still persists.

4

hmm, connecting the interface should have made the error vanish from syslog, this is weird as process-control clearly allows sched_setattr (which is syscall 314 (on x86 at least))

5

Double checked it, you’re absolutely right, that error is not in syslog anymore. However, audio decoding still fails, the “Playbin element is not valid” error persists.

6

ah, good, so the snap confinement should not be in your way anymore at least … you could try to strace it at runtime (using snap run --strace ...). probably it expects some files, configs libs etc in different places than your snap provides or some such (you could use layouts to re-map that) … also make sure you have a pulseaudio daemon running the snap can connect to …

8

Finally I had time to sort this out. The solution, as usual, was something trivial: GST_PLUGIN_PATH must be set.

For future reference, the key to figure out the problem was to temporary set GST_DEBUG=5 in my wrapper script.

Thank you @ogra for the help with finding the required plugs.

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