[Ffmpeg-devel] problem decoding blank/black mpg. Gives 2 vertical strips when frame is saved

[Pranav Desai]

Hello All,

Hope this is the right mailing list for this questions. Let me know if it
isnt.

I am doing some testing on blank frame detection using lavc to detect
commercial. I am using some code from mythtv commflag. So I thought I will
start by testing it on a blank mpg itself.

I created a blank/black mpg using the output_example.c provided with ffmpeg.
I made all the Y values to 0 and UV values 128 in fill_yuv_image(). I am not
sure if this the right way to do it, but it does generate a blank/black mpg
(I can attach it if needed).

I then use the avcodec_example.cpp provided here (
http://www.inb.uni-luebeck.de/~boehme/libavcodec_update.html). This link is
on the ffmpeg doc pages. This program saves the first 5 frames of an mpg
video.

Below is a part of the code.
When the frame is converted to RGB, it seems to correctly give a blank
image. But if YUV is used , there are 2 vertical white stripes on the image.
I have attached a jpg version of the frame saved using the program below.

I am not sure what am I doing wrong.

I would really appreciate if someone could help me out with this.

Thanks for taking the time to read this and let me know if you need the
above mentioned code. I can send it as a separate mail.

Thanks
-Pranav

-------------------------------------------------------------------
  while(av_read_frame(pFormatCtx, &packet)>=0)
    {
        // Is this a packet from the video stream?
        if(packet.stream_index==videoStream)
        {
            // Decode video frame
            avcodec_decode_video(pCodecCtx, pFrame, &frameFinished,
packet.data, packet.size);

            // Did we get a video frame?
            if(frameFinished)
            {
                // Convert the image from its native format to RGB
                img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24,
                    (AVPicture*)pFrame, pCodecCtx->pix_fmt,
pCodecCtx->width, pCodecCtx->height);

                // Save the frame to disk
                if(++i<=5) {
                    //SaveFrame(pFrameRGB, pCodecCtx->width,
pCodecCtx->height, i);
                    SaveFrame(pFrame, pCodecCtx->width, pCodecCtx->height,
i);
                }
            }
        }

        // Free the packet that was allocated by av_read_frame
        av_free_packet(&packet);
   }
-------------------------------------------------------------------
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