/dev/dsp to RTP

Victor Sudakov vas at mpeks.tomsk.su
Fri Sep 16 04:50:30 UTC 2011

John-Mark Gurney wrote:
> > Excuse me for asking in this developers' list, but I have tried
> > freebsd-questions and Google without much success.
> > 
> > What software can I use to obtain sound from /dev/dsp and multicast it
> > into the network? I need no sophisticated codecs, HTTP interfaces etc.
> > A plain 8-bit PCM sound that I could listen to with some multicast RTP
> > client like VLC would do.
> > 
> > Thanks in advance for any input.
> You could look at rat:
> http://mediatools.cs.ucl.ac.uk/nets/mmedia/wiki/RatWiki#RobustAudioToolRAT
> It does contain a GUI though.  It's be quite a few years since I used
> it though...

I remember once using mbone/vic, and there were also mbone/vat and
mbone/rat, but the whole mbone directory is now gone from the ports
tree. I cannot find rat in the ports tree any more.
> Other possibilities are ffmpeg or vlcserver.

Multicasting with ffmpeg works fine. The command line
ffmpeg -i file.mp3 -acodec copy -f rtp rtp:// -re

does send a multicast stream which can be listened to with VLC (but
not mplayer for some reason) on multiple hosts.

Now I need to figure out how to stream live sound from /dev/dsp. All
my attemps to record sound from a USB audio interface, as simple as

ffmpeg -f oss -i /dev/dsp1 out.wav

have resulted so far in a severely distorted growl instead of normal
voice. Do you know how to figure out the sampling rate and other
parameters of the sound card? "cat /dev/sndstat"  does not output
anything really useful.

The audio interface is not to blame because I use it all the time with
linphone for SIP calls.

Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru

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