提取motion vector

#include 
#include 

static AVFormatContext *fmt_ctx = NULL;
static AVCodecContext *video_dec_ctx = NULL;
static AVStream *video_stream = NULL;
static const char *src_filename = NULL;

static int video_stream_idx = -1;
static AVFrame *frame = NULL;
static AVPacket pkt;
static int video_frame_count = 0;

static int decode_packet(int *got_frame, int cached)
{
    int decoded = pkt.size;

    *got_frame = 0;

    if (pkt.stream_index == video_stream_idx) {
        int ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error decoding video frame (%s)\n", av_err2str(ret));
            return ret;
        }

        if (*got_frame) {
            int i;
            AVFrameSideData *sd;

            video_frame_count++;
            sd = av_frame_get_side_data(frame, AV_FRAME_DATA_MOTION_VECTORS);
            if (sd) {
                const AVMotionVector *mvs = (const AVMotionVector *)sd->data;
                for (i = 0; i < sd->size / sizeof(*mvs); i++) {
                    const AVMotionVector *mv = &mvs[i];
                    printf("%d,%2d,%2d,%2d,%4d,%4d,%4d,%4d,0x%"PRIx64"\n",
                           video_frame_count, mv->source,
                           mv->w, mv->h, mv->src_x, mv->src_y,
                           mv->dst_x, mv->dst_y, mv->flags);
                }
            }
        }
    }

    return decoded;
}

static int open_codec_context(int *stream_idx,
                              AVFormatContext *fmt_ctx, enum AVMediaType type)
{
    int ret;
    AVStream *st;
    AVCodecContext *dec_ctx = NULL;
    AVCodec *dec = NULL;
    AVDictionary *opts = NULL;
    /*
     * 1.封装格式上下文
     * 2.流类型eg:video,audio
     * 3.指定流的序号（-1自动选择）
     * 4.尝试找到关联流
     * 5.如果非空则会返回指定流的解码器
     * 6.目前没有定义
     *
     *
     * 成功会返回一个非负流编号
     * 没有找到则返回AVERROR_STREAM_NOT_FOUND
     */

    ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
    if (ret < 0) {
        /*
         * av_get_media_type_string
         * 返回一个描述流类型的枚举字符串
         */
        fprintf(stderr, "Could not find %s stream in input file '%s'\n",
                av_get_media_type_string(type), src_filename);
        return ret;
    } else {
        //保存找到的流编号和流
        *stream_idx = ret;
        st = fmt_ctx->streams[*stream_idx];

        /* find decoder for the stream */
        dec_ctx = st->codec;
        dec = avcodec_find_decoder(dec_ctx->codec_id);
        if (!dec) {
            fprintf(stderr, "Failed to find %s codec\n",
                    av_get_media_type_string(type));
            return AVERROR(EINVAL);
        }

        /* Init the video decoder */
        av_dict_set(&opts, "flags2", "+export_mvs", 0);//增加了提取移动矢量参数
        if ((ret = avcodec_open2(dec_ctx, dec, &opts)) < 0) {
            fprintf(stderr, "Failed to open %s codec\n",
                    av_get_media_type_string(type));
            return ret;
        }
    }

    return 0;
}

int main(int argc, char **argv)
{
    int ret = 0, got_frame;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s , argv[0]);
        exit(1);
    }
    src_filename = argv[1];

    av_register_all();

    if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
        fprintf(stderr, "Could not open source file %s\n", src_filename);
        exit(1);
    }

    if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        exit(1);
    }

    if (open_codec_context(&video_stream_idx, fmt_ctx, AVMEDIA_TYPE_VIDEO) >= 0) {
        video_stream = fmt_ctx->streams[video_stream_idx];
        video_dec_ctx = video_stream->codec;
    }

    av_dump_format(fmt_ctx, 0, src_filename, 0);

    if (!video_stream) {
        fprintf(stderr, "Could not find video stream in the input, aborting\n");
        ret = 1;
        goto end;
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate frame\n");
        ret = AVERROR(ENOMEM);
        goto end;
    }

    printf("framenum,source,blockw,blockh,srcx,srcy,dstx,dsty,flags\n");

    /* initialize packet, set data to NULL, let the demuxer fill it */
    //并不会init data和size
    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    /* read frames from the file */
    while (av_read_frame(fmt_ctx, &pkt) >= 0) {
        AVPacket orig_pkt = pkt;
        do {
            ret = decode_packet(&got_frame, 0);
            if (ret < 0)
                break;
            pkt.data += ret;
            pkt.size -= ret;
        } while (pkt.size > 0);
        av_packet_unref(&orig_pkt);
    }

    /* flush cached frames */
    pkt.data = NULL;
    pkt.size = 0;
    do {
        decode_packet(&got_frame, 1);
    } while (got_frame);

end:
    avcodec_close(video_dec_ctx);
    avformat_close_input(&fmt_ctx);
    av_frame_free(&frame);
    return ret < 0;
--------------------- 
作者：cwenlu 
来源：CSDN 
原文：https://blog.csdn.net/u012098794/article/details/53954437 
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