ALSA equivalent to /dev/audio dump?

Question

This will be my poorest question ever...

On an old netbook, I installed an even older version of Debian, and toyed around a bit. One of the rather pleasing results was a very basic MP3 player (using libmpg123), integrated for adding background music to a little application doing something completely different. I grew rather fond of this little solution.

In that program, I dumped the decoded audio (from mpg123_decode()) to /dev/audio via a simple fwrite().

This worked fine - on the netbook.

Now, I came to understand that /dev/audio was something done by OSS, and is no longer supported on newer (ALSA) machines. Sure enough, my laptop (running a current Linux Mint) does not have this device.

So apparently I have to use ALSA instead. Searching the web, I've found a couple of tutorials, and they pretty much blow my mind. Modes, parameters, capabilities, access type, sample format, sample rate, number of channels, number of periods, period size... I understand that ALSA is a powerful API for the ambitious, but that's not what I am looking for (or have the time to grok). All I am looking for is how to play the output of mpg123_decode (the format of which I don't even know, not being an audio geek by a long shot).

Can anybody give me some hints on what needs to be done?

tl;dr

How do I get ALSA to play raw audio data?

Answer 1

And ten years later, the "actual" answer is found: That's the wrong way to do it in the first place.

libmpg123 comes with a companion library, libout123, which abstracts the underlying audio system for you. Based on libmpg123 example code:

#include <stdlib.h>
#include "mpg123.h"
#include "out123.h"

int main()
{
    mpg123_handle * _mpg_handle;
    out123_handle * _out_handle;
    double rate, channels, encoding;
    size_t position, buffer_size;
    unsigned char * buffer;
    char filename[] = "Example.mp3";

    mpg123_open( _mpg_handle, filename );
    mpg123_getformat( _mpg_handle, &rate, &channels, &encoding );
    out123_open( _out_handle, NULL, NULL );
    mpg123_format_none( _mpg_handle );
    mpg123_format( _mpg_handle, rate, channels, encoding );
    out123_start( _out_handle, rate, channels, encoding );

    buffer_size = mpg123_outblock( _mpg_handle );
    buffer = malloc( buffer_size );

    do
    {
        mpg123_read( _mpg_handle, buffer.get(), buffer_size, &position );
        out123_play( _out_handle, buffer.get(), position );
    } while ( position );

    out123_close( _out_handle );
    mpg123_close( _mpg_handle );
    free( buffer );
}