[LAU] Request for advice: remote Linux server playing audio on local Windows system

[Nikhil Nair]

Hi,

I'm pretty new to Linux audio, but a project I'm working on is going to
need me to generate musical notes on a remote Linux server, in
(near-)realtime (i.e. changing the sound output based on realtime events).
I have basically no familiarity with MIDI etc., but the easiest interface
I've found for the starting and stopping of notes, so far, is the
FluidSynth API.  That's not the issue, however: the trick is getting the
audio back to my Windows machine with low-ish latency, and in reasonable quality.

To add a little interest to the scenario..., my Windows machine is also
behind NAT and a firewall.  The ping round-trip time is under 30 ms,
though, so I'm hoping latencies of around 200 ms might be possible.

Just to make life more interesting, I'd rather not have to use X Windows at
all on the remote machine, as I'm blind, and haven't even begun to think
about the ins and outs of accessibility of a remote X server (and, frankly,
would rather just not go there for now).

(The application I'm working on may interest you, BTW: I'm converting
financial data, particularly currency price charts, into soundscapes, for
"visualising" recent price movements.  If it were just a one-off, I could
convert it into an audio file and download it; but, instead, I want it to
be interacctive, so I can rewind through the image, step backward or
forward frame by frame, etc.  I'm going to have fun with this!)

I've been considering a few methods of getting the audio to my Windows
machine, but none of the options I've come up with so far seem to quite
work as I want.  Here's what I've considered.

1.  Send audio to JACK, then send it to the Asterisk PBX via the App_Jack
application; listen to the audio via a softphone on the Windows machine,
connecting to the Asterisk server via SIP.  Sound quality wouldn't be ideal
- 8KHz mono - but I could live with that.  Unfortunately, it looks like
App_Jack doesn't successfully connect to a JACK server: a bug report was
lodged about it over 3 years ago, marked severe, but doesn't seem to have
been fixed as yet.

2.  Send audio via Jack and a streamer (probably DarkIce) to an Icecast2
server; then use a media player such as WinAmp or MPlayer.  The problem
here is buffering: 10-20 seconds of latency just isn't acceptable for the
realtime aspects of the project, and I don't know if there's a way to get a
media player to do unbuffered playback (a quick Google search seemed to
indicate not).

3.  Use netJACK1 to play audio direct from JACK (that's the only one of the
3 networked-JACK solutions mentioned on the JACK website that's recommended
for use over a WAN).  Unfortunately, once I dug into this, it looks like
the assumption is that the audio will be played on a Linux box: there
doesn't seem to be any provision for having the Windows machine as the one
doing the audio playing.  I did have a quick look at netJACK2, but that
seems to assume the two machines are on the same LAN - you don't even
specify the IP address to connect to!

4.  I wondered about using PulseAudio.  However, that seems quite tricky to
set up without X on the remote machine, and I'm not at all clear about the
NAT traversal issue.

5.  I also wondered about NAS: I gather it's very outdated, but it sounds
like about what I'm after.  However, I couldn't find a Windows download;
and FluidSynth doesn't have a NAS interface, as far as I understand it.
TiMidity does, though, so I'd just need to work out how to send it MIDI
events from software...

Tunneling through a forwarded port (using ssh) may help in some aspects,
but I'm not sure.  AT least, it adds an extra set of possibilities, as do
VPNs.

As you can see, I've been wracking my brains over this for a couple of
days, and while I've felt I'm really close on more than one occasion, I've
not quite got there.  Any input would be very much appreciated!

Alternatively, if there's a better place for me to be asking this question,
a pointer would be very helpful.

Cheers,

Nikhil.