基于ffmpeg-0.10 SDK的音频重采样

这个示例代码实现了基于FFmpeg-0.10 SDK的音频重采样，也可用于实现定点转浮点计算。

1. 声明

/*  ffmpeg_sdk.h */
#include <stdio.h>
#include <stdlib.h>

#ifdef __cplusplus
extern "C" {
#endif

#include "libavutil/imgutils.h"
#include "libavutil/opt.h"
#include "libavcodec/avcodec.h"
#include "libavutil/mathematics.h"

/* open log */
#include "libavutil/log.h"

/* audio resample */
#include "libswresample/swresample.h"
/* end */

#ifdef __cplusplus
}
#endif

class FFmpegSDK{
public:
FFmpegSDK();
~FFmpegSDK();


#define INPUT_AUDIO_CHANNEL_LAYOUT   AV_CH_LAYOUT_MONO
#define INPUT_AUDIO_SAMPLE_FMT            AV_SAMPLE_FMT_S16
#define INPUT_AUDIO_SAMPLE_RATE          16000
private:
    SwrContext     *m_swrctx;


public:
    int32_t      init_swresample(int32_t in_audio_channel_layout, 
                                 enum AVSampleFormat in_audio_sample_fmt, int32_t in_audio_sample_rate);
    int32_t      destroy_swrsample();
    int32_t      swresample_doing(uint8_t** out_sample_buf, int32_t out_sample_cnt, 
                                const uint8_t** in_sample_buf, int32_t in_sample_cnt);


    
};
}

2. 定义

/*  ffmpeg_sdk.cpp */
int32_t FFmpegSDK::init_swresample(int32_t in_audio_channel_layout, 
        enum AVSampleFormat in_audio_sample_fmt, int32_t in_audio_sample_rate){
    m_swrctx = swr_alloc();
    if (m_swrctx == NULL){
        ERROR_LOG("Allocate swresample failed!\n");
        return -1;
    }

#if LIBSWRESAMPLE_VERSION_MINOR >= 17  // 


#else
    m_swrctx = swr_alloc_set_opts(m_swrctx,
            m_avctx->channel_layout,
            m_avctx->sample_fmt,
            m_avctx->sample_rate,
            in_audio_channel_layout,
            in_audio_sample_fmt,
            in_audio_sample_rate,
            0, NULL);

#endif


    int32_t ret = swr_init(m_swrctx);
    if (ret < 0){
        ERROR_LOG("swr_init(->) failed!\n");
        return -1;
    }

    return 0;
}

int32_t FFmpegSDK::destroy_swrsample(){
    return 0;
}

int32_t FFmpegSDK::swresample_doing(uint8_t** out_sample_buf, int32_t out_sample_cnt, 
            const uint8_t** in_sample_buf, int32_t in_sample_cnt){

    int32_t len = 0;

    len = swr_convert(m_swrctx, out_sample_buf, out_sample_cnt, 
                in_sample_buf, in_sample_cnt);
    if (len  < 0){
        char errmsg[1024];
        av_strerror(len, errmsg, sizeof(errmsg));
        ERROR_LOG("swr_convert!(%d)(%s)", len, errmsg); 
        return len;
    }
    return 0;
}

3. 调用 

int FFmpegSDK::init(){ 
    ret = init_swresample(INPUT_AUDIO_CHANNEL_LAYOUT,
            INPUT_AUDIO_SAMPLE_FMT,
            INPUT_AUDIO_SAMPLE_RATE);
    if (ret < 0){
        ERROR_LOG("init swresample failed!");
        return false;
    }
    。。。
}

int FFmpegSDK::run(){
    
    AVCodecContext *m_avctx;
    。。。
    m_avctx->channel_layout = AV_CH_LAYOUT_MONO;
    m_avctx->sample_fmt       = AV_SAMPLE_FMT_FLT;
    m_avctx->sample_rate      = 16000;

    float *out_buf= new float[1024];
    memset(out_buf, 0, 1024 * sizeof(float));
     。。。
     ret = swresample_doing((uint8_t**)&out_buf, 1024,
                (const uint8_t**)&in_buf, 1024);
    。。。
}