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• OpenCL generating YUV420P black pixel

  2 mai 2021, par Albert Tinon

  I'm working on an FFmpeg OpenCL filter for converting GoPro Max .360 files in Google EAC projected files.
For doing that I need to "stack" the 2 input streams to a twice height output.
It is working very well at a realtime speed. (The working code is in comment)

  


  For going further I need to replace some pixels with some specific colors.
I wrote some macros for making RGB->YUV conversion. But I get only some green or pink pixel (only grey is OK).
this is my test code (with stacking in comment)

  


  #define Y(R,G,B) 0.299 * R + 0.587 * G + 0.114 * B
#define U(R,G,B) -0.147 * R - 0.289 * G + 0.436 * B
#define V(R,G,B) 0.615 * R - 0.515 * G - 0.100 * B
#define YUV(R,G,B) (float4)(Y(R,G,B),U(R,G,B),V(R,G,B),0)

__kernel void gopromax_stack(__write_only image2d_t dst,
                                __read_only  image2d_t gopromax_front,
                                __read_only  image2d_t gopromax_rear)
{
    const sampler_t sampler = (CLK_NORMALIZED_COORDS_FALSE |
                               CLK_FILTER_NEAREST);
    
    float4 val;
    int2 dst_size = get_image_dim(dst);
    int2 loc = (int2)(get_global_id(0), get_global_id(1));
    int split_loc = dst_size.y/2;

        if (loc.y < split_loc)
        {
          // working code for stacking
          //  val = read_imagef(gopromax_front, sampler, (int2)(loc.x, loc.y));

          // testing to put grey (working)
            val = YUV(0.5f,0.5f,0.5f);
        }
        else
        {
          // working code for stacking
          //  val = read_imagef(gopromax_rear, sampler, (int2)(loc.x, loc.y-split_loc));

          // testing to put black (gives green !)
            val = YUV(0,0,0);
        }

    if ((loc.xcode>

  


  I tried many think I cannot succeed to generate black or anything except grey.
What did I make wrong ?
I supposed that my pixels are YUV because I specified yuv420p as the format in my filter :

  


  -filter_complex '[0:0]format=yuv420p,hwupload[a] , [0:4]format=yuv420p,hwupload[b], [a][b]gopromax_opencl, hwdownload,format=yuv420p'


  


  The source streams are in hevc / nv12.

  


  Thanks all for your help.

  


• ffmpeg how to end video with a black frame/solid color

  10 mai 2021, par request

  I'm scaling 2 videos of different sizes and hstack them side by side together.

  


  If the length of the two videos is different and for example the first one is over, then it shows the last frame of that video the whole time. I want it to show nothing / a black frame until the other video is over

  


  My code so far :

  


  ffmpeg -i vid1.mp4 -i vid2.mp4 -filter_complex "[1][0]scale2ref[2nd][ref];[ref][2nd]hstack" -vsync 0 output.mp4


  


  How could this be achieved ? (something with tpad or stop_mode maybe ?)

  


  Here are two sample videos to test with :

  


  testvid1

  


  testvid1

  


• ffmpeg how to remove black borders when resizing an image

  3 juin 2021, par Mapg

  I am creating some thumbnails using FFmpeg and I see that some black borders are created when I resize them.

  


  I guess this is happening because the video source dimension doesn't match exactly the target dimension, so FFmpeg fills out the blank space with this black color.

  


  My question is ...

  


  Can I change this "black color" used by FFmpeg by default so I can match these extra borders added with the background of my application ?

  


  If this is not possible ...

  


  Can I convert these black borders to a transparent area so I can create a PNG to match my background which has a different color (a kind of light green)

  


  I have attached an example where you will see two black pixels height in the bottom zone of the picture.

  


  This is what I want to convert to transparent or being able to choose my own color.

  


  Any idea to solve this issue will be very helpful for me ?

  


  Thank you very much in advance !

  


  Mapg