ffmpeg学习九：音频编码前奏-ubuntu下录音和播放

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上一篇博客，我们把一个Yuv编码格式的视频文件编码为H264格式。那么接下来，自然要学习下音频编码了。在学习音频编码之前，我们先看看ubuntu下如何采集声音和播放声音。

录音

录制5秒钟的一段音频。
audio_recorder.c:

/*created by Jinwei Liu*/
#define ALSA_PCM_NEW_HW_PARAMS_API  #include <alsa/asoundlib.h>  int main(int argc,char **argv) {  long loops;  int rc;  int size;  snd_pcm_t *handle;  snd_pcm_hw_params_t *params;  unsigned int val;  int dir;  snd_pcm_uframes_t frames;  char *buffer;  FILE * fd_out;if(argc!=2){printf("usage:./a.out outfile\n");}/* Open PCM device for recording (capture). */  rc = snd_pcm_open(&handle, "default",  SND_PCM_STREAM_CAPTURE, 0);  if (rc < 0) {  fprintf(stderr,  "unable to open pcm device: %s\n",  snd_strerror(rc));  exit(1);  }  /* Allocate a hardware parameters object. */  snd_pcm_hw_params_alloca(&params);  /* Fill it in with default values. */  snd_pcm_hw_params_any(handle, params);  /* Set the desired hardware parameters. */  /* Interleaved mode */  snd_pcm_hw_params_set_access(handle, params,  SND_PCM_ACCESS_RW_INTERLEAVED);  /* Signed 16-bit little-endian format */  snd_pcm_hw_params_set_format(handle, params,  SND_PCM_FORMAT_S16_LE);  /* Two channels (stereo) */  snd_pcm_hw_params_set_channels(handle, params, 2);  /* 11025 bits/second sampling rate (CD quality) */  val = 11025;  snd_pcm_hw_params_set_rate_near(handle, params,  &val, &dir);  /* Set period size to 32 frames. */  //frames = 32;  // snd_pcm_hw_params_set_period_size_near(handle,  //                             params, &frames, &dir);  /* Write the parameters to the driver */  rc = snd_pcm_hw_params(handle, params);  if (rc < 0) {  fprintf(stderr,  "unable to set hw parameters: %s\n",  snd_strerror(rc));  exit(1);  }  /* Use a buffer large enough to hold one period */  snd_pcm_hw_params_get_period_size(params,  &frames, &dir);  size = frames * 4; /* 2 bytes/sample, 2 channels */  buffer = (char *) malloc(size);  /* We want to loop for 5 seconds */  snd_pcm_hw_params_get_period_time(params,  &val, &dir);  loops = 5000000 / val;  fd_out = fopen(argv[1],"w+");while (loops > 0) {  loops--;  rc = snd_pcm_readi(handle, buffer, frames);  if (rc == -EPIPE) {  /* EPIPE means overrun */  fprintf(stderr, "overrun occurred\n");  snd_pcm_prepare(handle);  } else 

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