// 输入pcm参数
int64_t src_ch_layout = AV_CH_LAYOUT_STEREO;
int src_rate = 48000;
enum AVSampleFormat src_sample_fmt = AV_SAMPLE_FMT_DBL;
int src_nb_channels = 0;
uint8_t **src_data = //...
int src_linesize = //...
int src_nb_samples = 1024;

// 重采样后输出pcm参数
int64_t dst_ch_layout = AV_CH_LAYOUT_STEREO;
int dst_rate = 44100;
enum AVSampleFormat dst_sample_fmt = AV_SAMPLE_FMT_S16;
int dst_nb_channels = 0;
uint8_t **dst_data = NULL;
int dst_linesize;
int dst_nb_samples;
int max_dst_nb_samples;

// 输出文件
FILE *dst_file= fopen("./debug/out.pcm", "wb");
if (!dst_file) {exit(1);}
int dst_bufsize;const char* fmt;int ret;

// 重采样实例
struct SwrContext *swr_ctx;
swr_ctx = swr_alloc();
if(!swr_ctx){exit(1);}

// 设置重采样参数
av_opt_set_int(swr_ctx, "in_channel_layout", src_ch_layout, 0);
av_opt_set_int(swr_ctx, "in_sample_rate", src_rate, 0);
av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", src_sample_fmt, 0);

av_opt_set_int(swr_ctx, "out_channel_layout", dst_ch_layout, 0);
av_opt_set_int(swr_ctx, "out_sample_rate", dst_rate, 0);
av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", dst_sample_fmt, 0);

// 初始化重采样
if((ret=swr_init(swr_ctx))<0){exit(1);}

// 计算出输出采样数量
max_dst_nb_samples = dst_na_samples = 
  av_rescale_rnd(src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
dst_nb_channels = av_get_channel_layout_nb_channels(dst_ch_layout);
// 分配输出缓存内存
ret = av_sample_alloc_array_and_samples(&dst_data, &dst_linesize,dst_nb_channels, dst_nb_samples, dst_sample_fmt, 0);
if(ret<0){exit(1);}

// ...

fclose(dst_file);
if(src_data)
  av_freep(&src_data[0]);
av_freep(&src_data);
if(dst_data)
  av_freep(&dst_data[0]);
av_freep(&dst_data);

swr_free(&swr_ctx);

do{
  //..... 填充src_data
  int64_t delay = swr_get_delay(swr_ctx, src_rate); // swr_ctx中还可以输出的帧数
  dst_nb_samples = av_rescale_rnd(delay+src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
  if(dst_nb_samples > max_dst_nb_samples){ // 需要重新分配内存
    av_freep(&dst_data[0]);
    ret = av_samples_alloc(dst_data, &dst_linesize, dst_nb_channels,
            dst_nb_samples, dst_sample_fmt, 1);
    if(ret < 0) break;
    max_dst_nb_samples = dst_nb_samples;
  }

  ret = swr_convert(swr_ctx, dst_data, dst_nb_samples, NULL,0);
  if(ret<0){exit(1);}
  dst_bufsize = av_samples_get_buffer_size(&dst_linesize, dst_nb_channels, ret, dst_sample_fmt, 1);
  if(dst_bufsize<0){exit(1);}
  fwrite(dst_data[0],1,dst_bufsize,dst_file);
}(/*仍有未读取的输入帧*/);
// 处理缓存中的数据
ret = swr_convert(swr_ctx, dst_data, dst_nb_samples, NULL, 0);
if (ret < 0) {}
dst_bufsize = av_samples_get_buffer_size(&dst_linesize, dst_nb_channels,
                                          ret, dst_sample_fmt, 1);
if (dst_bufsize < 0) {exit(1);}
printf("flush in:%d out:%d\n", 0, ret);
fwrite(dst_data[0], 1, dst_bufsize, dst_file);