[speex-dev] Speex latency

Rolando Martins rolando.martins at ent.efacec.pt
Fri Mar 21 07:38:00 PST 2003

        What sould be the capture and playback buffer size in 8,16,32 khz
for the Alsa system?
        Can this also causing latency?
        In the server side I have:
        -A thread that reads the input from mic (capture) ands copies to
main buffer.
        -The main loop encodes and sends it to the client ( it's read the
data from the main buffer)

        -A thread for interacting with alsa, as soon as it has data on the
main buffer it's to the Alsa device
        -The main loop reads from socket, decodes the frame and copies it to
the main buffer

        As time goes by I start to notice an increase of latency.

<p><p>        Rolando Martins

<p>> -----Original Message-----
> From:	Jean-Marc Valin [SMTP:jean-marc.valin at hermes.usherb.ca]
> Sent:	Sexta-feira, 21 de Março de 2003 15:08
> To:	speex
> Cc:	Rolando Martins
> Subject:	Re: [speex-dev] Speex latency
>  > What kind of latency is expected using 8,16,32 khz?
> Depending on the sampling rate, the latency is 30-36 ms (frame size is
> 20 ms). 
> > I am trying to do a realtime stream server, and I am having latency
> above
> > >500ms ( I capture the sound using the mic, encode it and send it to the
> > client).
> > I am using ALSA system, a SB128 PCI and a 800Mhz P3 . What can I do to
> lower
> > the latency?
> > 
> > I tried a test : arecord -t raw | speexenc - - | speexdec - and I found
> that
> > I also have a 500 ms latency.
> There are likely 3 problems with your setup:
> 1) arecord might have a big latency (probably reads the audio big chunks
> at a time)
> 2) speexenc/speexdec has a larger latency than the codec itself (which
> you get using libspeex) because of the packets/pages in the Ogg file.
> 3) The pipes all do some buffering which probably causes additional
> latency.
> 	Jean-Marc
> -- 
> Jean-Marc Valin, M.Sc.A.
> LABORIUS (http://www.gel.usherb.ca/laborius)
> Université de Sherbrooke, Québec, Canada
--- >8 ----
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