FFmpeg音频解码

FFmpeg音频解码和上一章的视频解码流程差不多。
区别在视频有像素格（YUV RGB）式而音频有采样格式（PCM AAC）、采样率、声道布局。

• 采样率
• 声道布局
  搭配 DSP可以合成各种声音的特效

case MODE_NORMAL:
                //原生播放
                system->playSound(sound, 0, false, &channel);
                LOGI("%s","fix normal");
                break;
case MODE_LUOLI:
                //萝莉
                //DSP digital signal process
                //dsp -> 音效 创建fmod中预定义好的音效
                //FMOD_DSP_TYPE_PITCHSHIFT dsp，提升或者降低音调用的一种音效
                system->createDSPByType(FMOD_DSP_TYPE_PITCHSHIFT,&dsp);
                //设置音调的参数
                dsp->setParameterFloat(FMOD_DSP_PITCHSHIFT_PITCH,2.5);

                system->playSound(sound, 0, false, &channel);
                //添加到channel
                channel->addDSP(0,dsp);
                LOGI("%s","fix luoli");
                break;

case MODE_JINGSONG:
                //惊悚
                system->createDSPByType(FMOD_DSP_TYPE_TREMOLO,&dsp);
                dsp->setParameterFloat(FMOD_DSP_TREMOLO_SKEW, 0.5);
                system->playSound(sound, 0, false, &channel);
                channel->addDSP(0,dsp);

                break;
case MODE_DASHU:
                //大叔
                system->createDSPByType(FMOD_DSP_TYPE_PITCHSHIFT,&dsp);
                dsp->setParameterFloat(FMOD_DSP_PITCHSHIFT_PITCH,0.8);

                system->playSound(sound, 0, false, &channel);
                //添加到channel
                channel->addDSP(0,dsp);
                LOGI("%s","fix dashu");
                break;
case MODE_GAOGUAI:
                //搞怪
                //提高说话的速度
                system->playSound(sound, 0, false, &channel);
                channel->getFrequency(&frequency);
                frequency = frequency * 1.6;
                channel->setFrequency(frequency);
                LOGI("%s","fix gaoguai");
                break;
case MODE_KONGLING:
                //空灵
                system->createDSPByType(FMOD_DSP_TYPE_ECHO,&dsp);
                dsp->setParameterFloat(FMOD_DSP_ECHO_DELAY,300);
                dsp->setParameterFloat(FMOD_DSP_ECHO_FEEDBACK,20);
                system->playSound(sound, 0, false, &channel);
                channel->addDSP(0,dsp);
                LOGI("%s","fix kongling");
                break;

#include <android/log.h>
#define LOGI(FORMAT,...) __android_log_print(ANDROID_LOG_INFO,"",FORMAT,##__VA_ARGS__);
#define LOGE(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR,"",FORMAT,##__VA_ARGS__);

#define MAX_AUDIO_FRME_SIZE 48000 * 4

//封装格式
#include "libavformat/avformat.h"
//解码
#include "libavcodec/avcodec.h"
//缩放
#include "libswscale/swscale.h"
//重采样
#include "libswresample/swresample.h"

JNIEXPORT void JNICALL Java_com_ffmpegplayer_Player_sound
  (JNIEnv *env, jobject jobj, jstring input_jstr, jstring output_jstr){
    const char* input_cstr = (*env)->GetStringUTFChars(env,input_jstr,NULL);
    const char* output_cstr = (*env)->GetStringUTFChars(env,output_jstr,NULL);
    LOGI("%s","sound");
    //注册组件
    av_register_all();
    AVFormatContext *pFormatCtx = avformat_alloc_context();
    //打开音频文件
    if(avformat_open_input(&pFormatCtx,input_cstr,NULL,NULL) != 0){
        LOGI("%s","无法打开音频文件");
        return;
    }
    //获取输入文件信息
    if(avformat_find_stream_info(pFormatCtx,NULL) < 0){
        LOGI("%s","无法获取输入文件信息");
        return;
    }
    //获取音频流索引位置
    int i = 0, audio_stream_idx = -1;
    for(; i < pFormatCtx->nb_streams;i++){
        if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO){
            audio_stream_idx = i;
            break;
        }
    }

    //获取解码器
    AVCodecContext *codecCtx = pFormatCtx->streams[audio_stream_idx]->codec;
    AVCodec *codec = avcodec_find_decoder(codecCtx->codec_id);
    if(codec == NULL){
        LOGI("%s","无法获取解码器");
        return;
    }
    //打开解码器
    if(avcodec_open2(codecCtx,codec,NULL) < 0){
        LOGI("%s","无法打开解码器");
        return;
    }
    //压缩数据
    AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
    //解压缩数据
    AVFrame *frame = av_frame_alloc();
    //frame->16bit 44100 PCM 统一音频采样格式与采样率
    SwrContext *swrCtx = swr_alloc();

    //重采样设置参数-------------start
    //输入的采样格式
    enum AVSampleFormat in_sample_fmt = codecCtx->sample_fmt;
    //输出采样格式16bit PCM
    enum AVSampleFormat out_sample_fmt = AV_SAMPLE_FMT_S16;
    //输入采样率
    int in_sample_rate = codecCtx->sample_rate;
    //输出采样率
    int out_sample_rate = 44100;
    //获取输入的声道布局
    //根据声道个数获取默认的声道布局（2个声道，默认立体声stereo）
    //av_get_default_channel_layout(codecCtx->channels);
    uint64_t in_ch_layout = codecCtx->channel_layout;
    //输出的声道布局（立体声）
    uint64_t out_ch_layout = AV_CH_LAYOUT_STEREO;

    swr_alloc_set_opts(swrCtx,
          out_ch_layout,out_sample_fmt,out_sample_rate,
          in_ch_layout,in_sample_fmt,in_sample_rate,
          0, NULL);
    swr_init(swrCtx);

    //输出的声道个数
    int out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);

    //重采样设置参数-------------end

    //16bit 44100 PCM 数据
    uint8_t *out_buffer = (uint8_t *)av_malloc(MAX_AUDIO_FRME_SIZE);

    FILE *fp_pcm = fopen(output_cstr,"wb");

    int got_frame = 0,index = 0, ret;
    //不断读取压缩数据
    while(av_read_frame(pFormatCtx,packet) >= 0){
        //解码
        ret = avcodec_decode_audio4(codecCtx,frame,&got_frame,packet);

        if(ret < 0){
            LOGI("%s","解码完成");
        }
        //解码一帧成功
        if(got_frame > 0){
            LOGI("解码：%d",index++);
            swr_convert(swrCtx, &out_buffer, MAX_AUDIO_FRME_SIZE,frame->data,frame->nb_samples);
            //获取sample的size
            int out_buffer_size = av_samples_get_buffer_size(NULL, out_channel_nb,
                    frame->nb_samples, out_sample_fmt, 1);
            fwrite(out_buffer,1,out_buffer_size,fp_pcm);
        }

        av_free_packet(packet);
    }

    fclose(fp_pcm);
    av_frame_free(&frame);
    av_free(out_buffer);

    swr_free(&swrCtx);
    avcodec_close(codecCtx);
    avformat_close_input(&pFormatCtx);

    (*env)->ReleaseStringUTFChars(env,input_jstr,input_cstr);
    (*env)->ReleaseStringUTFChars(env,output_jstr,output_cstr);

}