ffmpeg实现mjpeg摄像头的采集-预览-拍照

　　摄像头输出是mjpeg格式的，需要实现在线预览功能，然后实现拍照功能

　　1.可以设置采集图像的分辨率，预览分辨率为640*480，可以自定义

　　2.ctrl+\ 拍照，ctrl+c 退出

void test() {
    if (signal(SIGQUIT, sigHandle) == SIG_ERR) {
        perror("set signal err");
    }
    if (signal(SIGINT, sigHandle) == SIG_ERR) {
        perror("set signal err");
    }
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVCodecContext *ifcodec_ctx, *ofcodec_ctx;
    AVCodec *icodec, *ocodec;
    AVStream *out_stream;
    AVFrame *pFrame, *pFrameYUV420, *pFrameBGR;
    struct SwsContext *in_conCtx, *out_conCtx;
    unsigned char *in_buffer, *out_buffer;
    AVPacket inpkg, outpkg;
    const char *in_filename;
    int ret, i;
    int got_picture;
    IplImage *image;
    int videoindex = -1;
    int frame_index = 0;
    int64_t start_time = 0, end_time = 0;
//    in_filename = "test.mp4";
    in_filename = "/dev/video1";
//    in_filename = "rtmp://219.216.87.170/live/test3";
//    out_filename = "rtmp://219.216.87.170/live/test2";

    av_register_all();
    avdevice_register_all();
    avformat_network_init();
    ifmt_ctx = avformat_alloc_context();
    ifmt_ctx->probesize = 20000000;
    ifmt_ctx->max_analyze_duration = 2000;

    AVDictionary* options = NULL;
    av_dict_set(&options, "fflags", "nobuffer", 0);
    av_dict_set(&options, "max_delay", "100000", 0);
    av_dict_set(&options, "framerate", "30", 0);
    av_dict_set(&options, "input_format", "mjpeg", 0);
    av_dict_set(&options, "video_size", "1920x1080", 0);
//    av_dict_set(&options, "video_size", "1280x720", 0);

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, &options)) < 0) {
        printf("open input file err\n");
        goto end;
    }
    av_dict_free(&options);
    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        printf("failed to retrieve input stream information\n");
        goto end;
    }
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoindex = i;
            break;
        }
        printf("codec %d:%d %d\n", i, ifmt_ctx->streams[i]->codec->codec_type,
                ifmt_ctx->streams[i]->codec->codec_id);
    }
//    exit(1);
    ifcodec_ctx = ifmt_ctx->streams[videoindex]->codec;
    icodec = avcodec_find_decoder(ifcodec_ctx->codec_id);
    if (icodec == NULL) {
        printf("icodec not find\n");
        goto end;
    }
    if (avcodec_open2(ifcodec_ctx, icodec, NULL) < 0) {
        printf("open icodec err\n");
        goto end;
    }
    printf("**************** input file info ******************\n");
    av_dump_format(ifmt_ctx, 0, in_filename, 0);

//    avformat_alloc_output_context2(&ofmt_ctx, NULL, "flv", out_filename);
    ofmt_ctx = avformat_alloc_context();
    if (!ofmt_ctx) {
        printf("could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }
    ofmt = av_guess_format("mjpeg", NULL, NULL);
    ofmt_ctx->oformat = ofmt;
    out_stream = avformat_new_stream(ofmt_ctx, NULL);
    if (!out_stream) {
        printf("failed allocating output stream\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }
    ofcodec_ctx = out_stream->codec;
    ofcodec_ctx->codec_id = ofmt->video_codec;
    ofcodec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;
    ofcodec_ctx->pix_fmt = AV_PIX_FMT_YUVJ420P;
    ofcodec_ctx->width = ifcodec_ctx->width;
    ofcodec_ctx->height = ifcodec_ctx->height;
    ofcodec_ctx->time_base.den = 30;
    ofcodec_ctx->time_base.num = 1;
    printf("timebase %d %d\n", ofcodec_ctx->time_base.den,
            ofcodec_ctx->time_base.num);
//    ofcodec_ctx->bit_rate = 1000000;
//    ofcodec_ctx->gop_size = 5;
//    ofcodec_ctx->me_range = 16;
//    ofcodec_ctx->max_qdiff = 4;
//    ofcodec_ctx->qmin = 10;
//    ofcodec_ctx->qmax = 51;
//    ofcodec_ctx->qcompress = 0.6;
//    if (ofcodec_ctx->codec_id == AV_CODEC_ID_H264) {
//        av_opt_set(ofcodec_ctx->priv_data, "preset", "slow", 0);
//        ofcodec_ctx->max_b_frames = 1;
//    }

    out_stream->codec->codec_tag = 0;
    if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
        out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
    }

    ocodec = avcodec_find_encoder(ofcodec_ctx->codec_id);
    if (!ocodec) {
        printf("find encoder err\n");
        goto end;
    }
    if (avcodec_open2(ofcodec_ctx, ocodec, NULL) < 0) {
        printf("open encoder err\n");
        goto end;
    }

    /*******************************************/
    pFrame = av_frame_alloc();
    pFrameYUV420 = av_frame_alloc();
    pFrameBGR = av_frame_alloc();
    in_buffer = (unsigned char *) av_malloc(
            avpicture_get_size(AV_PIX_FMT_BGR24, 640, 480));
    avpicture_fill((AVPicture*) pFrameBGR, in_buffer, AV_PIX_FMT_BGR24, 640,
            480);
//    printf("fmt %d\twidth %d\theight %d\n", pFrameBGR->format, pFrameBGR->width,
//            pFrameBGR->height);
    out_buffer = (unsigned char *) av_malloc(
            avpicture_get_size(AV_PIX_FMT_YUV420P, ofcodec_ctx->width,
                    ofcodec_ctx->height));
    avpicture_fill((AVPicture*) pFrameYUV420, out_buffer, AV_PIX_FMT_YUV420P,
            ofcodec_ctx->width, ofcodec_ctx->height);

//    printf("fmt %d\twidth %d\theight %d\n", pFrameYUV420->format,
//            pFrameYUV420->width, pFrameYUV420->height);

    in_conCtx = sws_getContext(ifcodec_ctx->width, ifcodec_ctx->height,
            ifcodec_ctx->pix_fmt, 640, 480,
            AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);
    out_conCtx = sws_getContext(ifcodec_ctx->width, ifcodec_ctx->height,
            ifcodec_ctx->pix_fmt, ofcodec_ctx->width, ofcodec_ctx->height,
            ofcodec_ctx->pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
    image = cvCreateImageHeader(cvSize(640, 480),
    IPL_DEPTH_8U, 3);
    cvSetData(image, in_buffer, 640 * 3);
//    inpkg = (AVPacket*) av_malloc(sizeof(AVPacket));
//    outpkg = (AVPacket*) av_malloc(sizeof(AVPacket));

    start_time = av_gettime();
    pFrameYUV420->format = AV_PIX_FMT_YUV420P;
    pFrameYUV420->width = ofcodec_ctx->width;
    pFrameYUV420->height = ofcodec_ctx->height;
    av_new_packet(&outpkg, ofcodec_ctx->width * ofcodec_ctx->height * 3);
    while (av_read_frame(ifmt_ctx, &inpkg) >= 0 && runFlag) {
        inpkg.dts = av_rescale_q_rnd(inpkg.dts,
                ifmt_ctx->streams[videoindex]->time_base,
                ifmt_ctx->streams[videoindex]->codec->time_base,
                (enum AVRounding) (AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
        inpkg.pts = av_rescale_q_rnd(inpkg.pts,
                ifmt_ctx->streams[videoindex]->time_base,
                ifmt_ctx->streams[videoindex]->codec->time_base,
                (enum AVRounding) (AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
        //decode
        if (inpkg.stream_index == videoindex) {
            ret = avcodec_decode_video2(ifcodec_ctx, pFrame, &got_picture,
                    &inpkg);
            if (ret < 0) {
                printf("decode err\n");
                exit(-1);
            }
            if (got_picture) {
                pFrame->pts = av_frame_get_best_effort_timestamp(pFrame);

                sws_scale(in_conCtx,
                        (const unsigned char * const *) pFrame->data,
                        pFrame->linesize, 0, ifcodec_ctx->height,
                        pFrameBGR->data, pFrameBGR->linesize);
//                printf("bgr fmt %d\twidth %d\theight %d\n", pFrameBGR->format,
//                        pFrameBGR->width, pFrameBGR->height);
                cvShowImage("camera", image);
                cvWaitKey(1);

                if (flag == 1) {
                    char out_filename[30];
                    memset(out_filename, 0, sizeof(out_filename));
                    sprintf(out_filename, "%d.jpg", frame_index);
                    printf("encode  frame %d\n", frame_index++);
                    if (!(ofmt->flags & AVFMT_NOFILE)) {
                        ret = avio_open(&ofmt_ctx->pb, out_filename,
                        AVIO_FLAG_WRITE);
                        if (ret < 0) {
                            printf("could not open output url ‘%s‘\n",
                                    out_filename);
                            goto end;
                        }
                    }
                    printf(
                            "**************** output file info ******************\n");
                    av_dump_format(ofmt_ctx, 0, out_filename, 1);
                    ret = avformat_write_header(ofmt_ctx, NULL);
                    if (ret < 0) {
                        printf("error occurred when opening output URL\n");
                        goto end;
                    }
                    sws_scale(out_conCtx,
                            (const unsigned char * const *) pFrame->data,
                            pFrame->linesize, 0, ofcodec_ctx->height,
                            pFrameYUV420->data, pFrameYUV420->linesize);
                    //                printf("yuv420 fmt %d\twidth %d\theight %d\n",
                    //                        pFrameYUV420->format, pFrameYUV420->width,
                    //                        pFrameYUV420->height);

                    got_picture = 0;
                    pFrameYUV420->pts = pFrame->pts;
                    ret = avcodec_encode_video2(ofcodec_ctx, &outpkg,
                            pFrameYUV420, &got_picture);
                    if (ret < 0) {
                        printf("encode err\n");
                        goto end;
                    }
                    if (got_picture == 1 && flag == 1) {
                        av_write_frame(ofmt_ctx, &outpkg);
                        av_free_packet(&outpkg);
                        av_write_trailer(ofmt_ctx);
                    }
                    flag = 0;
                }

            }
        }
        //encode

        av_free_packet(&inpkg);
        end_time = av_gettime();
        printf("fps:%2f\n", (float) 1000000 / (end_time - start_time));
        start_time = end_time;
    }
    end: sws_freeContext(in_conCtx);
    sws_freeContext(out_conCtx);
    free(in_buffer);
    free(out_buffer);
    av_free(pFrameYUV420);
    av_free(pFrameBGR);
    avcodec_close(ifcodec_ctx);
    avcodec_close(ofcodec_ctx);
    avformat_close_input(&ifmt_ctx);
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_close(ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);
    if (ret < 0 && ret != AVERROR_EOF) {
        printf("Error occurred.\n");
        exit(-1);
    }
    exit(0);
}

　　代码是从标准的视频采集/转码程序改过来的，是测试程序，没有啥封装，看起来比较乱。