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Re: [Linphone-developers] Implementing sound support for non-standard ha

From: Daniel Kabs [ML]
Subject: Re: [Linphone-developers] Implementing sound support for non-standard hardware
Date: Tue, 21 Dec 2004 12:11:00 +0100

On Mon, 20 Dec 2004, Simon Morlat <address@hidden> wrote:
> This interface is NOT expected to change in 1.0.x...

Very good! So I can continue my work using linphone 0.12.2 until you
publish the new release on your web page.

> > But the following call to snd_card_read() may read less bytes.
> No I don't think so. If I'm right, f->gran is set to be the same as
> the minimum granularity returned by the SndCard.

Let me summarize our e-mail conversation on that problem here:
- The sound card does not have a "granularity".
- It only has a certain latency that can be requested using the call
  sndcard.c::snd_card_probe(). But when the oss read filter is
  initialized, it does not probe the sound card's latency.
- Instead the filter uses r->gran=(512*r->freq)/8000;
  to calculate the granularity (in msossread.c::ms_oss_read_start()).
- snd_card_read() must fill the user supplied buffer entirely. That's
  the condition for the whole thing to work.

> > Isn't this a problem? And why is the return value of
> snd_card_read() ignored?
> For the same reason, if it works well we will get what we expect, and
> if not  we have no way to recover and this is a bug !

I am still pondering how this filter-fifo-queueing works, when every
20ms there is an input of 256 samples (512 bytes from the soundcard),
but only 160 samples are output through the RTP packet.

Daniel Kabs
Kaiserslautern, Germany

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