Bug 300853

Phonon has its own sound settings. To get OSS to show there you'll need to entirely disable PulseAudio.

I don't even have pulseaudio installed. I now started with a completely fresh user. Setup phonon to use vlc-backend, logout, login, test sound -> vlc still wants to take alsa.

Where should I look at?

systemsettings

:D Where? I only can chose the backend and the devices - but none of the devices listed are working:
* Default
* Discard all samples (playback) or generate zero samples (capture)
Is there some hidden button for extended configuration, where I can explicitly say "oss, please!"?

might be that you have to remove the kde platform plugin for phonon, that most likely takes preference over the backend dependent listing.

    QList<QByteArray> knownSoundSystems;
    knownSoundSystems << "alsa" << "oss";

Tried different things:
I installed vlc without alsa-support -> device list is empty.
I renamed /usr/lib64/kde4/plugins/phonon_platform -> I get back a default-device - which uses phonon-gstreamer instead of vlc, although vlc is selected as preferred backend.
So I uninstalled phonon-gstreamer, leaving an empty device list :(

I also tried with most recent vlc from git, without success.
I am using oss4 (also latest mercurial), linux-3.4.0 (with gentoo-patchset) if that matters.

Seems as if vlc does not like to be started with --aout==dummy, when running with oss. I removed the line in libvlc.cpp, and I get sound :D
But still the devices list in systemsettings is empty.

simple test-programm:

#include <iostream>
#include <vlc/vlc.h>
#include <cstdio>
using namespace std;

int main() {
    libvlc_instance_t* libvlc = libvlc_new(0,0);
    libvlc_audio_output_t *first = libvlc_audio_output_list_get(libvlc);
    for( libvlc_audio_output_t *aout = first; aout; aout = aout->p_next) {
        char const* ss_nm = aout->psz_name;
        const int dev_cnt = libvlc_audio_output_device_count(libvlc, ss_nm);
        cout << ss_nm << " offers devices: " << dev_cnt << endl;
    }
    libvlc_audio_output_list_release(first);
}

output (I reenabled alsa in vlc):
alsa offers devices: 2
oss offers devices: 0
aout_file offers devices: 0
adummy offers devices: 0
amem offers devices: 0

So this is eather a problem in vlc, or in oss4.

I reported this upstream:
https://trac.videolan.org/vlc/ticket/6900

Created attachment 71529 [details]
Add a Default OSS-Device manually

Upstream says, that device_count of 0 is valid. So populating the devices by device_count won't work (at least for oss, JACK, Pulse). The patch attached adds an OSS-Device manually.
I hardcoded idName and longName to "/dev/dsp" and "Default OSS", because I don't know the vlc-API and if there is a function to determine if the user configured to use something else.

But another problem remains: I need to compile vlc without alsa-support, because if phonon-vlc recognizes the availability of alsa, it seems to discard any other sound system. Is there a way to determine, which sound system the user runs? Check the existence of /dev/oss \ /dev/snd \ /dev/dsp? As there are only alsa and oss (->knownSoundSystems) to be checked, I think this won't be too difficult.

> Check the existence of /dev/oss \ /dev/snd \ /dev/dsp? As there are
> only alsa and oss (->knownSoundSystems) to be checked, I think this won't be
> too difficult. 

The attached patch checks for existence of /dev/dsp and /dev/snd/ and sets 
preferredSoundSystem accordingly. The debug()-statements would better be 
QMessageBoxes or system notifications.
I tested it on two computers, one running alsa, the other one oss4, both with 
vlc-support for alsa and oss, both having no problem to set up working 
devices.

Created attachment 71531 [details]
vlc-oss.patch

Thinking about the solution, emulation came in my mind. alsa can emulate oss-devices, so the existance of /dev/dsp also could mean that alsa is running with oss-emulation turned on. I did not look at alsa-emulation in oss, but I know it exists.
So to see if native oss is running, a check for /proc/opensound/ is more meaningful (/proc/asound for native alsa).

>>> QDir("/proc/asound").exists()
False
>>> QDir("/proc/opensound").exists()
True

The question that remains is whether to offer the user to chose those emulated devices ("OSS Emulation" if /proc/asound and /dev/dsp exist).

If you like the approach, I can modify the patch. If you don't just tell me how it would be done better :)

Please verify that current pvlc master fixes the issue, we don't have setups to test that sort of stuff.

(In reply to comment #14)
> Please verify that current pvlc master fixes the issue, we don't have setups
> to test that sort of stuff.

Yes, it works (after changing the preferred device to oss). Thanks for the fix!