NDK--利用FFmpeg进行音频解码

#include <jni.h>
#include <string>
#include <android/log.h>
#include <android/native_window_jni.h>
#include <unistd.h>

extern "C" {
//编码
#include "libavcodec/avcodec.h"
//封装格式处理
#include "libavformat/avformat.h"
#include "libswresample/swresample.h"
//像素处理
#include "libswscale/swscale.h"
}

#define  LOG_TAG    "aruba"
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

extern "C"
JNIEXPORT void JNICALL
Java_com_aruba_ffmpegapplication_DecodeActivity_decodeAudio(JNIEnv *env, jobject instance,
                                                            jstring inputFilePath_,
                                                            jstring outputFilePath_) {
    const char *inputFilePath = env->GetStringUTFChars(inputFilePath_, 0);
    const char *outputFilePath = env->GetStringUTFChars(outputFilePath_, 0);

    //注册FFmpeg中各大组件
    av_register_all();

    //打开文件
    AVFormatContext *formatContext = avformat_alloc_context();
    if (avformat_open_input(&formatContext, inputFilePath, NULL, NULL) != 0) {
        LOGE("打开失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        env->ReleaseStringUTFChars(outputFilePath_, outputFilePath);
        return;
    }

    //将文件信息填充进AVFormatContext
    if (avformat_find_stream_info(formatContext, NULL) < 0) {
        LOGE("获取文件信息失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        env->ReleaseStringUTFChars(outputFilePath_, outputFilePath);
        return;
    }

    //获取视频流的编解码器上下文
    AVCodecContext *codecContext = NULL;
    int audio_stream_idx = -1;
    for (int i = 0; i < formatContext->nb_streams; ++i) {
        if (formatContext->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {//如果是视频流
            codecContext = formatContext->streams[i]->codec;
            audio_stream_idx = i;
            break;
        }
    }

    if (codecContext == NULL) {
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        env->ReleaseStringUTFChars(outputFilePath_, outputFilePath);
        return;
    }

    //根据编解码器上下文的id获取视频流解码器
    AVCodec *codec = avcodec_find_decoder(codecContext->codec_id);
    //打开解码器
    if (avcodec_open2(codecContext, codec, NULL) < 0) {
        LOGE("解码失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        env->ReleaseStringUTFChars(outputFilePath_, outputFilePath);
        return;
    }

    //开始读每一帧
    //存放压缩数据
    AVPacket *pkt = (AVPacket *) (av_malloc(sizeof(AVPacket)));
    av_init_packet(pkt);

    //存放解压数据
    AVFrame *picture = av_frame_alloc();

    int picture_ptr = 0;

    //音频转码组件上下文
    SwrContext *swrContext = swr_alloc();
//    struct SwrContext *swr_alloc_set_opts(struct SwrContext *s,
//                                          int64_t out_ch_layout, enum AVSampleFormat out_sample_fmt, int out_sample_rate,
//                                          int64_t  in_ch_layout, enum AVSampleFormat  in_sample_fmt, int  in_sample_rate,
//                                          int log_offset, void *log_ctx);
    //AV_CH_LAYOUT_STEREO:双声道  AV_SAMPLE_FMT_S16:量化格式 16位 codecContext->sample_rate:采样率 Hz
    swr_alloc_set_opts(swrContext, AV_CH_LAYOUT_STEREO, AV_SAMPLE_FMT_S16,
                       codecContext->sample_rate,//输出采样率和输入采样率应相同
                       codecContext->channel_layout, codecContext->sample_fmt,
                       codecContext->sample_rate, 0, NULL
    );


    //原音频通道数
    int channel_count = av_get_channel_layout_nb_channels(codecContext->channel_layout);
    //单通道最大存放转码数据 所占字节 = 采样率*量化格式 / 8
    int out_size = 44100 * 16 / 8;
    uint8_t *out = (uint8_t *) (av_malloc(out_size));

    //文件
    FILE *output_file = fopen(outputFilePath, "wb");

    while (av_read_frame(formatContext, pkt) == 0) {//读到每一帧的压缩数据存放在AVPacket
        if (pkt->stream_index == audio_stream_idx) {
            //解码
            avcodec_decode_audio4(codecContext, picture, &picture_ptr, pkt);

            LOGE("picture_ptr %d", picture_ptr);
            if (picture_ptr > 0) {
                //转码
                swr_convert(swrContext, &out, out_size,
                            (const uint8_t **) (picture->data), picture->nb_samples);

//                int av_samples_get_buffer_size(int *linesize, int nb_channels, int nb_samples,
//                                               enum AVSampleFormat sample_fmt, int align);
                //缓冲区真实大小
                int size = av_samples_get_buffer_size(NULL, channel_count, picture->nb_samples,
                                                      AV_SAMPLE_FMT_S16, 1);
                fwrite(out, sizeof(uint8_t), size, output_file);
            }

        }
        av_free_packet(pkt);
    }

    //关闭文件
    fclose(output_file);
    //释放资源
    av_freep(out);
    swr_free(&swrContext);
    av_frame_free(&picture);
    avcodec_close(codecContext);
    avformat_free_context(formatContext);
    env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
    env->ReleaseStringUTFChars(outputFilePath_, outputFilePath);
}