[alsa-devel] redirecting audio to another desktop machine

[Viral Mehta]

Hi,

> -----Original Message-----
> From: alsa-devel-bounces at alsa-project.org [mailto:alsa-devel-
> bounces at alsa-project.org] On Behalf Of Hans-Kristian Arntzen
> Sent: Monday, June 21, 2010 7:21 PM
> To: Viral Mehta
> Cc: alsa-devel at alsa-project.org
> Subject: Re: [alsa-devel] redirecting audio to another desktop machine
>
> On 06/21/2010 02:10 PM, Viral Mehta wrote:
> >
> >> On 06/21/2010 12:00 PM, alsa-devel-request at alsa-project.org wrote:
> >>
> >>> Date: Mon, 21 Jun 2010 14:57:00 +0530
> >>> From: Viral Mehta<Viral.Mehta at lntinfotech.com>
> >>> Subject: [alsa-devel] redirecting audio to another desktop machine
> >>> To: "alsa-devel at alsa-project.org"<alsa-devel at alsa-project.org>
> >>> Message-ID:
> >>>
> <70376CA23424B34D86F1C7DE6B9973430254343B3E at VSHINMSMBX01.vshodc.lntinfo
> tech.com>
> >>>
> >>> Content-Type: text/plain; charset="us-ascii"
> >>>
> >>> Hi list,
> >>>
> >>> I have an embedded device running linux kernel and a minimal
> filesystem.
> >>>
> >>> I want to access this device remotely which means I should be able
> to connect to the device just like we do Remote Desktop over ethernet.
> >>> I am able to do this. I am able to send key-event and framebuffer
> data whenever my desktop machine connects to the device.
> >>>
> >>> But, I am not able to send audio data on remote side.
> >>> I am really not sure which device file (/dev/snd/ ???) I should
> read and capture the data and should send across....
> >>> Or can I read the playback device ? I think NO.
> >>> Do I need to create some kind of virtual sound device ?
> >>>
> >>> Any pointers/suggestions are appreciated.
> >>>
> >>> Thanks,
> >>> Viral
> >>>
> >>>
> >>>
> >>>
> >> If you want to reroute an ALSA application over the network, you can
> use
> >> output plugins. Afaik, both PulseAudio and RSound provides plugins
> for
> >> this. You generally want to set up a virtual device in .asoundrc or
> >> similar.
> >> -- Hans-Kristian Arntzen
> >>
> > Hi,
> > thanks for the reply.
> >
> > Let me make sure I understood it in general..... Is it possible to
> use same plugins (or any other) if my embedded device is connected to
> my  desktop machine via USB (assuming that I have all USB data transfer
> mechanism/drivers underlying).
> >
> > If I setup a virtual device in .asoundrc, audio (or say aplay)
> applications will pass audio data to my virtual device ??
> > Do I also need to create any such virtual interface from kernel code
> as well ?
> >
> >
> With output plugins for ALSA, you can in general do whatever you want.
> The plugins will receive audio data, and they can do anything. When you
> say you want to output to your device via USB cable, I'm not sure if
> that is supplied ootb. I assumed you wanted to output via ethernet.
> Pulse might do USB, but I'm not sure.
>
> In any case, your output plugin will probably look something like this:
>
> pcm.usb_device {
>     type usb_output # there's no output plugin like this, just a random
> name to illustrate
>     device "your device"
> }
>
> Then you could use aplay -Dusb_device.

Thanks for the reply.
I think neither Pulse nor Rsound supports USB.

So, I believe I will have to write something mine.
First thing as you explained, I would write one plugin.

And then my ALSA user space application will throw data on that virtual
Device; so I need to have one kernel space driver as well, right ?
Is it in anycase relevant to Sound Dummy (/dev/null) device ?

And in my Virtual Driver, I may do usb_register and then submit data through
URBs. Am I on a right path ?

Thanks,
Viral



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