Convert raw image buffer into JPEG using LIBAVCODEC

Question

I have a raw image buffer (in memory) captured from a camera that I want to convert into JPEG (for reducing size). The problem is that saving these images into .pgm format results into a huge file size that I can't afford due to the memory limitations and latency involved in saving a huge file of this size (a constraint in the application I am working on).

I want to know how do I compress/encode an image buffer into .jpg format using LIBAVCODEC? My image capture code is in C.

Is there a reason you need to use libav instead of an image-specific, or even jpeg-specific, library? — blahdiblah

arash kordi arash kordi · Accepted Answer · 2012-09-24T10:19:46

this code works with YUV raw images. I got segfault trying to encode an RGB raw image. but you can use swscale() to convert RGB to YUV

int main()
{
    int ret;
    AVFrame *frame;
    AVPacket pkt;

    av_register_all();

    AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
    if (!codec)
    {
        printf("Codec not found\n");
        exit(1);
    }

    AVCodecContext* c = avcodec_alloc_context3(codec);
    if (!c)
    {
        printf("Could not allocate video codec context\n");
        exit(1);
    }

    c->bit_rate = 400000;
    c->width = 320;
    c->height = 200;
    c->time_base= (AVRational){1,25};
    c->pix_fmt = AV_PIX_FMT_YUVJ420P;

    if (avcodec_open2(c, codec, NULL) < 0)
    {
        printf("Could not open codec\n");
        exit(1);
    }

    frame = avcodec_alloc_frame();
    if (!frame)
    {
        printf("Could not allocate video frame\n");
        exit(1);
    }
    frame->format = c->pix_fmt;
    frame->width  = c->width;
    frame->height = c->height;

    ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height, c->pix_fmt, 32);
    if (ret < 0)
    {
        printf("Could not allocate raw picture buffer\n");
        exit(1);
    }

    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    /* prepare a dummy image */
    /* Y */
    for(int y=0;y<c->height;y++) {
        for(int x=0;x<c->width;x++) {
            frame->data[0][y * frame->linesize[0] + x] = x + y;
        }
    }

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


    frame->pts = 1;

    int got_output = 0;
    ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
    if (ret < 0)
    {
        printf("Error encoding frame\n");
        exit(1);
    }

    if (got_output)
    {
        printf("got frame\n");
        FILE* f = fopen("x.jpg", "wb");
        fwrite(pkt.data, 1, pkt.size, f);
        av_free_packet(&pkt);
    }

    avcodec_close(c);
    av_free(c);
    av_freep(&frame->data[0]);
    avcodec_free_frame(&frame);
    printf("\n");

    return 0;
}

Convert raw image buffer into JPEG using LIBAVCODEC

1 Answers