ffmpeg YUV420 to RGB24 converts only one row

Question

I'm trying to convert my YUV420p image to RGB24 in c++ and create bitmap from byte array in c#.

My image size is 1920 w * 1020 h and ffmpeg decoder give me 3 planars for data with linesizes = {1920, 960, 960}. But after sws_scale I'm getting RGB picture with only one plane with linesize = 5760. It does not looks correct: I should get (5760 * h), not just only one row of data. What I'm doing wrong?

 //c++ part
    if (avcodec_receive_frame(m_decoderContext, pFrame) == 0)
    {
        //RGB
        sws_ctx = sws_getContext(m_decoderContext->width,
            m_decoderContext->height,
            m_decoderContext->pix_fmt,
            m_decoderContext->width,
            m_decoderContext->height,
            AV_PIX_FMT_RGB24,
            SWS_BILINEAR,
            NULL,
            NULL,
            NULL
        );

        sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data, pFrame->linesize,
            0, pFrame->height,
            pFrameRGB->data, pFrameRGB->linesize);


//c# part (im reading data from pipe and its equal to c++ part)------------------------------------------------------------------
        byte[] rgbch = new byte[frameLen];
        for (int i=0; i<frameLen; i++)
        {
            rgbch[i] = Convert.ToByte(pipe.ReadByte());
        }

        if (rgbch.Length > 0)
        {
            var arrayHandle = System.Runtime.InteropServices.GCHandle.Alloc(rgbch,
    System.Runtime.InteropServices.GCHandleType.Pinned);

            var bmp = new Bitmap(1920, 1080,
                3,
                System.Drawing.Imaging.PixelFormat.Format24bppRgb,
                arrayHandle.AddrOfPinnedObject()
            );

            pictureBox1.Image = bmp;
        }

Why do you think it is not correct? You give in planar pixel data, get out interleaved pixel data where each row has a size of 3 * 1920, and the memory region in total is 3 * 1920 * height. — Rudolfs Bundulis
Well, I do not understand where is that 3*1920*height memory region. I got only one row of 3 * 1920 in pFrameRGB->data... For full image I need all other rows?.. — Aleksey
What is the return value of sws_scale ? It should be the number of rows in the output buffer - pFrameRGB->data. If its not 1 then your assumption is wrong. If it really is 1 then something is going wrong. — Rudolfs Bundulis
I've missed return value of sws_scale.. With it I got right amount of "columns" in my buffer... so, basically, as I understand now linesize is not a size of data - it just show one row size in data? — Aleksey

Rudolfs Bundulis Rudolfs Bundulis · Accepted Answer · 2016-08-10T14:44:34

Your assumption that the linesize field of AVFrame is the total amount of data is not correct. As the name of the variable states it is the length of a single row, while the return value of sws_scale gives you the number of rows. Thus the total memory range size for the output bitmap is linesize multiplied by the return value.

ffmpeg YUV420 to RGB24 converts only one row

1 Answers