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• RGB to YUV conversion with libav (ffmpeg) triplicates image

  17 avril 2021, par José Tomás Tocino

  I'm building a small program to capture the screen (using X11 MIT-SHM extension) on video. It works well if I create individual PNG files of the captured frames, but now I'm trying to integrate libav (ffmpeg) to create the video and I'm getting... funny results.

  


  The furthest I've been able to reach is this. The expected result (which is a PNG created directly from the RGB data of the XImage file) is this :

  


  

  


  However, the result I'm getting is this :

  


  

  


  As you can see the colors are funky and the image appears cropped three times. I have a loop where I capture the screen, and first I generate the individual PNG files (currently commented in the code below) and then I try to use libswscale to convert from RGB24 to YUV420 :

  


  while (gRunning) {
        printf("Processing frame framecnt=%i \n", framecnt);

        if (!XShmGetImage(display, RootWindow(display, DefaultScreen(display)), img, 0, 0, AllPlanes)) {
            printf("\n Ooops.. Something is wrong.");
            break;
        }

        // PNG generation
        // snprintf(imageName, sizeof(imageName), "salida_%i.png", framecnt);
        // writePngForImage(img, width, height, imageName);

        unsigned long red_mask = img->red_mask;
        unsigned long green_mask = img->green_mask;
        unsigned long blue_mask = img->blue_mask;

        // Write image data
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                unsigned long pixel = XGetPixel(img, x, y);

                unsigned char blue = pixel & blue_mask;
                unsigned char green = (pixel & green_mask) >> 8;
                unsigned char red = (pixel & red_mask) >> 16;

                pixel_rgb_data[y * width + x * 3] = red;
                pixel_rgb_data[y * width + x * 3 + 1] = green;
                pixel_rgb_data[y * width + x * 3 + 2] = blue;
            }
        }

        uint8_t* inData[1] = { pixel_rgb_data };
        int inLinesize[1] = { in_w };

        printf("Scaling frame... \n");
        int sliceHeight = sws_scale(sws_context, inData, inLinesize, 0, height, pFrame->data, pFrame->linesize);

        printf("Obtained slice height: %i \n", sliceHeight);
        pFrame->pts = framecnt * (pVideoStream->time_base.den) / ((pVideoStream->time_base.num) * 25);

        printf("Frame pts: %li \n", pFrame->pts);
        int got_picture = 0;

        printf("Encoding frame... \n");
        int ret = avcodec_encode_video2(pCodecCtx, &pkt, pFrame, &got_picture);

//                int ret = avcodec_send_frame(pCodecCtx, pFrame);

        if (ret != 0) {
            printf("Failed to encode! Error: %i\n", ret);
            return -1;
        }

        printf("Succeed to encode frame: %5d - size: %5d\n", framecnt, pkt.size);

        framecnt++;

        pkt.stream_index = pVideoStream->index;
        ret = av_write_frame(pFormatCtx, &pkt);

        if (ret != 0) {
            printf("Error writing frame! Error: %framecnt \n", ret);
            return -1;
        }

        av_packet_unref(&pkt);
    }


  


  I've placed the entire code at this gist. This question right here looks pretty similar to mine, but not quite, and the solution did not work for me, although I think this has something to do with the way the line stride is calculated.

  


• How to convert from AV_PIX_FMT_BGRA to PIX_FMT_PAL8 ?

  29 juillet 2014, par Jona

  I’m having a hard time converting my images from AV_PIX_FMT_BGRA to PIX_FMT_PAL8. Unfortunately sws_getCachedContext doesn’t support the conversion to PIX_FMT_PAL8.

  What I’m trying to do is convert my images into a GIF video with higher quality output. It seems that PIX_FMT_PAL8 could potentially provide the higher quality output I’m looking for.

  According to this documentation I need to palettize the pixel data, but I have no clue how to do that.

  When the pixel format is palettized RGB (PIX_FMT_PAL8), the palettized
  image data is stored in AVFrame.data[0]. The palette is transported in
  AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is
  formatted the same as in PIX_FMT_RGB32 described above (i.e., it is
  also endian-specific). Note also that the individual RGB palette
  components stored in AVFrame.data[1] should be in the range 0..255.
  This is important as many custom PAL8 video codecs that were designed
  to run on the IBM VGA graphics adapter use 6-bit palette components.

  Any help or direction would be appreciated.

• avcodec/mediacodecdec : warn when input buffers are not configured with proper size

  5 septembre 2019, par Aman Gupta

  avcodec/mediacodecdec : warn when input buffers are not configured with proper size
  In rare circumstances, if the codec is not configured with the
  
  proper parameters the input buffers can be allocated with a size
  
  that's too small to hold an individual packet. Since MediaCodec
  
  expects exactly one incoming buffer with a given PTS, it is not
  
  valid to split data for a given PTS across two input buffers.
  See https://developer.android.com/reference/android/media/MediaCodec#data-processing:
    > Do not submit multiple input buffers with the same timestamp
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  

  • [DH] libavcodec/mediacodecdec.c