How to mention real image instead of dummy image in ffmpeg api-example.c

I am using video_encode_example function from api-example.c of FFmpeg, which basically creates 25 dummy images and encodes into a one second video. How ever i am unable to mention real images instead of dummy ones. If any one know how to do this for xcode objective C, pl submit a reply. Below is the function

/*
 * Video encoding example
 */
static void video_encode_example(const char *filename)
{
    AVCodec *codec;
    AVCodecContext *c= NULL;
    int i, out_size, size, x, y, outbuf_size;
    FILE *f;
    AVFrame *picture;
    uint8_t *outbuf, *picture_buf;

    printf("Video encoding\n");

    /* find the mpeg1 video encoder */
    codec = avcodec_find_encoder(CODEC_ID_MPEG1VIDEO);
    if (!codec) {
        fprintf(stderr, "codec not found\n");
        exit(1);
    }

    c= avcodec_alloc_context();
    picture= avcodec_alloc_frame();

    /* put sample parameters */
    c->bit_rate = 400000;
    /* resolution must be a multiple of two */
    c->width = 352;
    c->height = 288;
    /* frames per second */
    c->time_base= (AVRational){1,25};
    c->gop_size = 10; /* emit one intra frame every ten frames */
    c->max_b_frames=1;
    c->pix_fmt = PIX_FMT_YUV420P;

    /* open it */
    if (avcodec_open(c, codec) < 0) {
        fprintf(stderr, "could not open codec\n");
        exit(1);
    }

    f = fopen(filename, "wb");
    if (!f) {
        fprintf(stderr, "could not open %s\n", filename);
        exit(1);
    }

    /* alloc image and output buffer */
    outbuf_size = 100000;
    outbuf = malloc(outbuf_size);
    size = c->width * c->height;
    picture_buf = malloc((size * 3) / 2); /* size for YUV 420 */

    picture->data[0] = picture_buf;
    picture->data[1] = picture->data[0] + size;
    picture->data[2] = picture->data[1] + size / 4;
    picture->linesize[0] = c->width;
    picture->linesize[1] = c->width / 2;
    picture->linesize[2] = c->width / 2;

    /* encode 1 second of video */
    for(i=0;i<25;i++) {
        fflush(stdout);
        /* prepare a dummy image */
        /* Y */
        for(y=0;y<c->height;y++) {
            for(x=0;x<c->width;x++) {
                picture->data[0][y * picture->linesize[0] + x] = x + y + i * 3;
            }
        }

        /* Cb and Cr */
        for(y=0;y<c->height/2;y++) {
            for(x=0;x<c->width/2;x++) {
                picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2;
                picture->data[2][y * picture->linesize[2] + x] = 64 + x + i * 5;
            }
        }

        /* encode the image */
        out_size = avcodec_encode_video(c, outbuf, outbuf_size, picture);
        printf("enco开发者_如何学运维ding frame %3d (size=%5d)\n", i, out_size);
        fwrite(outbuf, 1, out_size, f);
    }

    /* get the delayed frames */
    for(; out_size; i++) {
        fflush(stdout);

        out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL);
        printf("write frame %3d (size=%5d)\n", i, out_size);
        fwrite(outbuf, 1, out_size, f);
    }

    /* add sequence end code to have a real mpeg file */
    outbuf[0] = 0x00;
    outbuf[1] = 0x00;
    outbuf[2] = 0x01;
    outbuf[3] = 0xb7;
    fwrite(outbuf, 1, 4, f);
    fclose(f);
    free(picture_buf);
    free(outbuf);

    avcodec_close(c);
    av_free(c);
    av_free(picture);
    printf("\n");
}

I didn't test it but may be if you are capturing the image in YUV420p format you can point the picture->data[0] to your captured byte pointer.

picture->data[0] = picture_buf; //put your data here, remove the dummy data insertion