FFmpeg解码视频帧为jpg图片保存到本地

    之前遇到一个需求是将视频一秒一秒解码成一帧一帧的图片，用户滑动选择时间节点（微信朋友圈发10秒视频的编辑界面）。开始我是用的MediaMetadataRetriever类来获取图片，但是对于分辨率比较大的视频（1920*1080）获取一个图片要0.7/0.8秒，太慢了。后来又用FFmpeg的命令来批量的解码视频成一帧一帧的图片，速度依然不快每张图片得耗费0.5秒左右的时间。最后还是用FFmpeg，不过不是用命令行，而是用NDK，发现c解码视频再转换为图片保存起来效率大大挺高，一秒钟能解码4、5张图片，c就是快啊，做一下总结。

附上源码：
http://download.csdn.net/download/qq_28284547/10031785
GitHub：https://github.com/kui92/FFmpegTools

    创建工程，注意要勾选上支持c++。

我从网上找到了编译好的FFmpeg文件，直接考到自己的工程里的。

配置gradle与CMakeLists
gradle

CMakeLists

cmake_minimum_required(VERSION 3.4.1)
include_directories(
${CMAKE_SOURCE_DIR}/src/main/cpp/include
)

add_library( # Sets the name of the library.
jxffmpegrun

         # Sets the library as a shared library.
         SHARED

         # Provides a relative path to your source file(s).

          src/main/cpp/cmdutils.c
          src/main/cpp/ffmpeg.c
          src/main/cpp/ffmpeg_filter.c
          src/main/cpp/ffmpeg_opt.c
          src/main/cpp/jx_ffmpeg_cmd_run.c
         )

add_library(avcodec SHARED IMPORTED)

add_library(avfilter SHARED IMPORTED)

add_library(avformat SHARED IMPORTED)

add_library(avutil SHARED IMPORTED)

add_library(swresample SHARED IMPORTED)

add_library(swscale SHARED IMPORTED)

add_library(fdk-aac SHARED IMPORTED)

set_target_properties(
avcodec
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libavcodec.so
)

set_target_properties(
avfilter
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libavfilter.so
)

set_target_properties(
avformat
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libavformat.so
)

set_target_properties(
avutil
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libavutil.so
)

set_target_properties(
swresample
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libswresample.so
)

set_target_properties(
swscale
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libswscale.so
)

set_target_properties(
fdk-aac
PROPERTIES IMPORTED_LOCATION
CMAKESOURCEDIR/src/main/jniLibs/ {ANDROID_ABI}/libfdk-aac.so
)

target_link_libraries( # Specifies the target library.
jxffmpegrun
log
android
fdk-aac
avcodec
avfilter
avformat
avutil
swresample
swscale
# Links the target library to the log library
# included in the NDK.
${log-lib} )

新建FfmpegTool类，编写native方法并生成头文件（头文件的生成方法可自行百度）

实现native方法

//实现native方法
#define  LOG_TAG    "videoplayer"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
/**
 * 将AVFrame(YUV420格式)保存为JPEG格式的图片
 *
 * @param width YUV420的宽
 * @param height YUV42的高
 *
 */
int MyWriteJPEG(AVFrame *pFrame,char *path,  int width, int height, int iIndex) {
    // 输出文件路径
    char out_file[1000] = {0};
    LOGD("path:%s", path);
    sprintf(out_file, "%stemp%d.jpg", path, iIndex);
    LOGD("out_file:%s", out_file);
    // 分配AVFormatContext对象
    AVFormatContext *pFormatCtx = avformat_alloc_context();

    // 设置输出文件格式
    pFormatCtx->oformat = av_guess_format("mjpeg", NULL, NULL);
    // 创建并初始化一个和该url相关的AVIOContext
    if (avio_open(&pFormatCtx->pb, out_file, AVIO_FLAG_READ_WRITE) < 0) {
        LOGD("Couldn't open output file.");
        return -1;
    }

    // 构建一个新stream
    AVStream *pAVStream = avformat_new_stream(pFormatCtx, 0);
    if (pAVStream == NULL) {
        return -1;
    }

    // 设置该stream的信息
    AVCodecContext *pCodecCtx = pAVStream->codec;

    pCodecCtx->codec_id = pFormatCtx->oformat->video_codec;
    pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
    pCodecCtx->pix_fmt = AV_PIX_FMT_YUVJ420P;
    pCodecCtx->width = width;
    pCodecCtx->height = height;
    pCodecCtx->time_base.num = 1;
    pCodecCtx->time_base.den = 25;

    // Begin Output some information
    av_dump_format(pFormatCtx, 0, out_file, 1);
    // End Output some information

    // 查找解码器
    AVCodec *pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
    if (!pCodec) {
        LOGD("Codec not found.");
        return -1;
    }
    // 设置pCodecCtx的解码器为pCodec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        LOGD("Could not open codec.");
        return -1;
    }

    //Write Header
    avformat_write_header(pFormatCtx, NULL);

    int y_size = pCodecCtx->width * pCodecCtx->height;

    //Encode
    // 给AVPacket分配足够大的空间
    AVPacket pkt;
    av_new_packet(&pkt, y_size * 3);

    //
    int got_picture = 0;
    int ret = avcodec_encode_video2(pCodecCtx, &pkt, pFrame, &got_picture);
    if (ret < 0) {
        LOGD("Encode Error.\n");
        return -1;
    }
    if (got_picture == 1) {
        //pkt.stream_index = pAVStream->index;
        ret = av_write_frame(pFormatCtx, &pkt);
    }

    av_free_packet(&pkt);

    //Write Trailer
    av_write_trailer(pFormatCtx);

    LOGD("Encode Successful.\n");

    if (pAVStream) {
        avcodec_close(pAVStream->codec);
    }
    avio_close(pFormatCtx->pb);
    avformat_free_context(pFormatCtx);

    return 0;
}




/**
 *方法的实现入口
 */
JNIEXPORT jint JNICALL Java_com_esay_ffmtool_FfmpegTool_decodToImage
        (JNIEnv * env, jclass mclass, jstring in, jstring dir, jint startTime, jint num){

    char * input=jstringTostring(env,in);
    char * parent=jstringTostring(env,dir);

    LOGD("input:%s",input);
    LOGD("parent:%s",parent);


    av_register_all();
    AVFormatContext *pFormatCtx = avformat_alloc_context();
    // Open video file
    if (avformat_open_input(&pFormatCtx, input, NULL, NULL) != 0) {
        LOGD("Couldn't open file:%s\n", input);
        return -1; // Couldn't open file
    }

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        LOGD("Couldn't find stream information.");
        return -1;
    }
    // Find the first video stream
    int videoStream = -1, i;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
            && videoStream < 0) {
            videoStream = i;
        }
    }
    if (videoStream == -1) {
        LOGD("Didn't find a video stream.");
        return -1; // Didn't find a video stream
    }

    // Get a pointer to the codec context for the video stream
    AVCodecContext *pCodecCtx = pFormatCtx->streams[videoStream]->codec;

    // Find the decoder for the video stream
    AVCodec *pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL) {
        LOGD("Codec not found.");
        return -1; // Codec not found
    }

    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        LOGD("Could not open codec.");
        return -1; // Could not open codec
    }
    // Allocate video frame
    AVFrame *pFrame = av_frame_alloc();

    if (pFrame == NULL) {
        LOGD("Could not allocate video frame.");
        return -1;
    }
    int64_t count = startTime;
    int frameFinished;
    //(*pCodecCtx).
    AVPacket packet;

    LOGD("start_time:%d",pFormatCtx->start_time);
    LOGD("pFormatCtx den:%d", pFormatCtx->streams[videoStream]->sample_aspect_ratio.den);
    LOGD("pFormatCtx num:%d", pFormatCtx->streams[videoStream]->sample_aspect_ratio.num);
    av_seek_frame(pFormatCtx,-1,(int64_t)count*AV_TIME_BASE,AVSEEK_FLAG_FRAME);
    while (av_read_frame(pFormatCtx, &packet) >= 0){
        if (packet.stream_index == videoStream){
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
            // 并不是decode一次就可解码出一帧
            if (frameFinished){
                if(count<(startTime+num)){
                    MyWriteJPEG(pFrame,parent, pCodecCtx->width,
                                pCodecCtx->height, count);
                    ++count;
                    av_seek_frame(pFormatCtx,-1,(int64_t)count*AV_TIME_BASE,AVSEEK_FLAG_FRAME);
                } else{
                    av_packet_unref(&packet);
                    LOGD("break:");
                    break;
                }

            }
        }
        av_packet_unref(&packet);
    }
    // Free the YUV frame
    av_free(pFrame);
    // Close the codecs
    avcodec_close(pCodecCtx);
    // Close the video file
    avformat_close_input(&pFormatCtx);
    return  0;
}

链接so库，在类FfmpegTool开头加入代码：

 static {
        System.loadLibrary("avutil");
        System.loadLibrary("fdk-aac");
        System.loadLibrary("avcodec");
        System.loadLibrary("avformat");
        System.loadLibrary("swscale");
        System.loadLibrary("swresample");
        System.loadLibrary("avfilter");
        System.loadLibrary("jxffmpegrun");
    }

//测试运行,在MainActivity中添加按钮执行如下方法，注意FfmpegTool.decodToImage方法是阻塞的，有时候耗时较长要放在子线程。
public void click2(View view){
        String path= "图片要保存的路径";
        String video="视频路径";
        FfmpegTool.decodToImage(video,path,0,60);
    }

最后再次附上源码：
http://download.csdn.net/download/qq_28284547/10031785
GitHub：https://github.com/kui92/FFmpegTools