capturing stdout from a piped open

zentara has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I've tried for a few hours, and I am at a roadblock. What I am trying to do, is pipe raw pcm sound from /dev/dsp to oggenc, and save it to a scalar. In the code below, I can create an ogg file, or dump the binary data to stdout. But I can't seem to capture the stdout from oggenc. I tried IO::Tee and a few other things, but I can't seem to capture the data I see flying by on the screen.

Does anyone know if this type of capture is possible?

#!/usr/bin/perl
use warnings;
use strict;
use Audio::DSP;

$|++;

my ($buf, $chan, $fmt, $rate) = (4096, 1, 16, 22050);

my $dsp = new Audio::DSP(buffer   => $buf,
                     channels => $chan,
                     format   => $fmt,
                     rate     => $rate);

$dsp->init() || die $dsp->errstr();

#this method dosn't work 
#close STDOUT; 
#my $ogg_out = ''; 
#open STDOUT, '>', \$ogg_out, or die "Couldn't redirect STDOUT to $ogg
+_out: $!"; 


#this will dump the encoded ogg to STDOUT 
my $pid = open(OGGIN, "| oggenc -Q -r -R 22050 --resample 8000 -C 1 -q
+ 2 -  ")  
                 or warn "No oggenc $!\n"; 

#this will dump it to a file 
#my $pid = open(OGGIN, "| oggenc -Q -r -R 22050 --resample #8000 -C 1 
+-q 2 - | cat > $0.ogg  ")
#                 or warn "No oggenc $!\n";

while (my $buffer = $dsp->dread(4096) )  {
     syswrite( OGGIN, $buffer, length($buffer) );
          }


# of course, cntrl-c out of the while loop never lets this print 
# but I include it to show what I'm after 
#print $ogg_out;
[download]

I'm not really a human, but I play one on earth. flash japh

Comment on capturing stdout from a piped open Download Code

Replies are listed 'Best First'.
Re: capturing stdout from a piped open by davidrw (Prior) on Aug 29, 2005 at 19:45 UTC
From `perldoc -f open`: You are not allowed to "open" to a command that pipes both in and out, but see the IPC::Open2 man- page, the IPC::Open3 manpage, and the Bidirec- tional Communication with Another Process entry in the perlipc manpage for alternatives. Take a look at `perldoc perlipc`, IPC::Open2 and IPC::Open3 ..	[reply] [d/l] [select]
Re: capturing stdout from a piped open by Joost (Canon) on Aug 29, 2005 at 20:22 UTC
You might take a look at IPC::Open3 / IPC::Open2, but I'd probably go for either: using a temporary file for the output. setting up oggenc to read directly from /dev/dsp and output to the perl script using `open OGG,"oggenc -r -C 1 /dev/dsp\|"` or something similar. Which option is more appropriate depends on what you plan to do with the encoded stream. updated spelling and oggenc options "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re: capturing stdout from a piped open by izut (Chaplain) on Aug 30, 2005 at 11:35 UTC
This works: `open STDOUT, ">", $ogg_out or die $!; ... close STDOUT;` [download] Igor S. Lopes - izut surrender to perl. your code, your rules.	[reply] [d/l]
Re^2: capturing stdout from a piped open by zentara (Cardinal) on Aug 30, 2005 at 14:01 UTC
I get errors when I try it. When I do `close STDOUT; my $ogg_out; open *STDOUT, ">", \$ogg_out or die $!;` [download] It starts to run, but quickly fails with `Failed writing data to output stream Broken pipe` [download] I'm not really a human, but I play one on earth. flash japh	[reply] [d/l] [select]
Re: capturing stdout from a piped open by zentara (Cardinal) on Aug 30, 2005 at 10:27 UTC
Thanks for the replies. I should have mentioned that oggenc will not work with IPC::Open3, and the piped open is the only thing that has given any output. My plan was to capture the encoded chunks and send it to a socket......to make a VOIP type of program. The temp file would work, but would introduce a delay in sending the audio. I need to send as it is being spoken, at least in 4k chunks. Maybe I need to capture the stdout file-descriptor of the piped-open? I'm not really a human, but I play one on earth. flash japh	[reply]