From owner-freebsd-stable  Sat Sep 12 04:58:38 1998
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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199809121006.MAA20647@labinfo.iet.unipi.it>
Subject: Re: sound driver (pcm) block size must <= 2000 ?
To: wilson@krdl.org.sg (Wilson Tam)
Date: Sat, 12 Sep 1998 12:06:16 +0200 (MET DST)
Cc: luigi@iet.unipi.it, freebsd-stable@FreeBSD.ORG
In-Reply-To: <Pine.BSF.3.96.980912105837.27335B-100000@witamach.krdl.org.sg> from "Wilson Tam" at Sep 12, 98 11:00:55 am
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> Luigi,
> 
> I have a problem with the pcm sound driver for my creative card.  The
> problem is when I try to issue the command: 
> 
>         dd if=/dev/dsp of=record.raw bs=8000 count=1
> 
> The size of output file 'record.raw' always equal to 2000 rather than 8000
> bytes specified by the 'bs'. However if I change the block size (bs)  to

well... to avoid too high latency, the audio driver defaults to using
0.25s of data unless you specify a different blocksize using the
appropriate ioctl().

This is not such a great idea i agree, but programs tend to use large
blocksizes like 64K in a rad() call, and this makes redirection from
/dev/audio almost unusable. While I or someone else write a more
general program for audio grabbing/editing, you might try to use
a blocksize <= 0.25s in your dd call to be sure that you do not get a
short read (or, i think there are options for dd to read the desired
amount of data).

cheers
luigi


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