ALSA Audio API录音与播放教程

Bertha 。 2023-03-04 14:27 13阅读 0赞

# A Tutorial on Using the ALSA Audio API #

Original: [http://www.equalarea.com/paul/alsa-audio.html][http_www.equalarea.com_paul_alsa-audio.html]

# Contents #

*  [Understanding Audio Interface][]
 *  [What a Typical Audio Application Does][]
 *  [A Minimal Playback Program][]
 *  [A Minimal Capture Program][]
 *  [A Minimal interrupt-driven Program][]
 *  [A Minimal Duplex Program][]
 *  [How To Do It][]
    
     *  [Opening The Device][]
     *  [Setting The Parameters][]
     *  [Receiving And Delivering Data][]
 *  [Why You Might Want To Forget About All Of This][]

**典型音频应用做法**

A typical audio application has this rough structure:

open_the_device();
          set_the_parameters_of_the_device();
          while (!done) {
               /* one or both of these */
               receive_audio_data_from_the_device();
    	   deliver_audio_data_to_the_device();
          }
          close the device

[A Minimal Playback Program][]**（播放）**

#include <stdio.h>
    	#include <stdlib.h>
    	#include <alsa/asoundlib.h>
    	      
    	main (int argc, char *argv[])
    	{
    		int i;
    		int err;
    		short buf[128];
    		snd_pcm_t *playback_handle;
    		snd_pcm_hw_params_t *hw_params;
    	
    		if ((err = snd_pcm_open (&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
    			fprintf (stderr, "cannot open audio device %s (%s)\n", 
    				 argv[1],
    				 snd_strerror (err));
    			exit (1);
    		}
    		   
    		if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
    			fprintf (stderr, "cannot allocate hardware parameter structure (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    				 
    		if ((err = snd_pcm_hw_params_any (playback_handle, hw_params)) < 0) {
    			fprintf (stderr, "cannot initialize hardware parameter structure (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_access (playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
    			fprintf (stderr, "cannot set access type (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_format (playback_handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
    			fprintf (stderr, "cannot set sample format (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_rate_near (playback_handle, hw_params, 44100, 0)) < 0) {
    			fprintf (stderr, "cannot set sample rate (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_channels (playback_handle, hw_params, 2)) < 0) {
    			fprintf (stderr, "cannot set channel count (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params (playback_handle, hw_params)) < 0) {
    			fprintf (stderr, "cannot set parameters (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		snd_pcm_hw_params_free (hw_params);
    	
    		if ((err = snd_pcm_prepare (playback_handle)) < 0) {
    			fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		for (i = 0; i < 10; ++i) {
    			if ((err = snd_pcm_writei (playback_handle, buf, 128)) != 128) {
    				fprintf (stderr, "write to audio interface failed (%s)\n",
    					 snd_strerror (err));
    				exit (1);
    			}
    		}
    	
    		snd_pcm_close (playback_handle);
    		exit (0);
    	}

A Minimal Capture Program（录音）

#include <stdio.h>
    	#include <stdlib.h>
    	#include <alsa/asoundlib.h>
    	      
    	main (int argc, char *argv[])
    	{
    		int i;
    		int err;
    		short buf[128];
    		snd_pcm_t *capture_handle;
    		snd_pcm_hw_params_t *hw_params;
    	
    		if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    			fprintf (stderr, "cannot open audio device %s (%s)\n", 
    				 argv[1],
    				 snd_strerror (err));
    			exit (1);
    		}
    		   
    		if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
    			fprintf (stderr, "cannot allocate hardware parameter structure (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    				 
    		if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) {
    			fprintf (stderr, "cannot initialize hardware parameter structure (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
    			fprintf (stderr, "cannot set access type (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
    			fprintf (stderr, "cannot set sample format (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, 44100, 0)) < 0) {
    			fprintf (stderr, "cannot set sample rate (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) {
    			fprintf (stderr, "cannot set channel count (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) {
    			fprintf (stderr, "cannot set parameters (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		snd_pcm_hw_params_free (hw_params);
    	
    		if ((err = snd_pcm_prepare (capture_handle)) < 0) {
    			fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
    				 snd_strerror (err));
    			exit (1);
    		}
    	
    		for (i = 0; i < 10; ++i) {
    			if ((err = snd_pcm_readi (capture_handle, buf, 128)) != 128) {
    				fprintf (stderr, "read from audio interface failed (%s)\n",
    					 snd_strerror (err));
    				exit (1);
    			}
    		}
    	
    		snd_pcm_close (capture_handle);
    		exit (0);
    	}

alsa project :[https://alsa-project.org/wiki/Main\_Page][https_alsa-project.org_wiki_Main_Page]

[http_www.equalarea.com_paul_alsa-audio.html]: http://www.equalarea.com/paul/alsa-audio.html
[Understanding Audio Interface]: http://www.equalarea.com/paul/alsa-audio.html#interfaces
[What a Typical Audio Application Does]: http://www.equalarea.com/paul/alsa-audio.html#basics
[A Minimal Playback Program]: http://www.equalarea.com/paul/alsa-audio.html#playex
[A Minimal Capture Program]: http://www.equalarea.com/paul/alsa-audio.html#captureex
[A Minimal interrupt-driven Program]: http://www.equalarea.com/paul/alsa-audio.html#interruptex
[A Minimal Duplex Program]: http://www.equalarea.com/paul/alsa-audio.html#duplexex
[How To Do It]: http://www.equalarea.com/paul/alsa-audio.html#howto
[Opening The Device]: http://www.equalarea.com/paul/alsa-audio.html#open
[Setting The Parameters]: http://www.equalarea.com/paul/alsa-audio.html#params
[Receiving And Delivering Data]: http://www.equalarea.com/paul/alsa-audio.html#io
[Why You Might Want To Forget About All Of This]: http://www.equalarea.com/paul/alsa-audio.html#forget
[https_alsa-project.org_wiki_Main_Page]: https://alsa-project.org/wiki/Main_Page