[alsa-devel] Strange Config: Fedora 8 running on Amazon EC2

[Sean McNamara]

Hi,

On Wed, Jan 28, 2009 at 10:20 PM, Patrick Lightbody
<patrick at lightbody.net> wrote:
> I have a strange request (which is why I'm sending directly to the dev
> list). I'm trying to run Flash video (v9 or v10) on Firefox 3 on a
> Fedora 8 image running on Amazon EC2. I don't actually want/need sound
> (it's of course technically not possible, since EC2 doesn't provide a
> sound card). Video playback (when watched through VNC) goes fine for a
> couple minutes, but then the browser and flash lock up entirely. I've
> looked for ways to tell Firefox and/or Flash to not send audio out,
> but I've come up empty so far. So now I'm hoping that fixing this
> error and putting in perhaps some sort of "no op" device might help
> out.
>

> I'm not positive the error is related to ALSA,

Neither am I -- but we can definitely give you the info you need to
test out null playback to see if it helps. It could still be a
video-related issue.

> though the fact that
> there appear to be a ton of the following logs just before the lockup
> is suspicious:
>
> ALSA lib confmisc.c:768:(parse_card) cannot find card '0'
> ALSA lib conf.c:3513:(_snd_config_evaluate) function
> snd_func_card_driver returned error: No such file or directory
> ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
> ALSA lib conf.c:3513:(_snd_config_evaluate) function snd_func_concat
> returned error: No such file or directory
> ALSA lib confmisc.c:1251:(snd_func_refer) error evaluating name
> ALSA lib conf.c:3513:(_snd_config_evaluate) function snd_func_refer
> returned error: No such file or directory
> ALSA lib conf.c:3985:(snd_config_expand) Evaluate error: No such file
> or directory
> ALSA lib pcm.c:2144:(snd_pcm_open_noupdate) Unknown PCM default
> ALSA lib pcm_hw.c:1240:(_snd_pcm_hw_open) Invalid value for card
>
> (these lines repeat over and over again until the crash happens, then
> it stops promptly)

Yeah, you will want to eliminate such problems regardless of whether
they are immediately fatal. The software (Flash) could have memory
leaks or something if it fails to get a soundcard.

>
> As you can see by the alsa-info output at the following URL, I don't
> have any running snd modules:
>
> http://www.alsa-project.org/db/?f=6b2431d0564b3638cdb798a6d1a21eb73982588c
>
> Similarly, I don't have any sound-related devices installed (ie:
> /dev/audio, etc). My hope in emailing this list is that there may be a
> solution that causes ALSA to no-op the requests that Firefox/Flash
> send it's way, potentially solving the lockup I'm experiencing.

Option 1 (less obvious unless you know where to look, but certainly
viable): http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html
<--- look up the "Null" plugin here. Drop a null plugin into
/etc/asound.conf as the default:

pcm.!default {
type null
}

This is exactly the "no-op" soft PCM that you want. AFAIK all the APIs
against this just return saying "OK, I've done it", and the
configuration space is as flexible as possible.

Option 2, which was my first guess before I remembered the link above:
You could install PulseAudio and either pipe the sound over the
network to your host, or load a null sink, then use ALSA<->pulse.

Alternatively, you could provide "support" for no-op sounds from both
PulseAudio _and_ ALSA clients by implementing both these options.

HTH,

Sean

>
> I would really appreciate any ideas that could be shared. Thank you very much!
>
> Patrick
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