xfade_opencl

Cross fade two videos with custom transition effect by using OpenCL.

It accepts the following options:

transition

Set one of possible transition effects.

custom

Select custom transition effect, the actual transition description will be picked from source and kernel options.

fade

wipeleft

wiperight

wipeup

wipedown

slideleft

slideright

slideup

slidedown

Default transition is fade.

source

OpenCL program source file for custom transition.

kernel

Set name of kernel to use for custom transition from program source file.

duration

Set duration of video transition.

offset

Set time of start of transition relative to first video.

The program source file must contain a kernel function with the given name, which will be run once for each plane of the output. Each run on a plane gets enqueued as a separate 2D global NDRange with one work-item for each pixel to be generated. The global ID offset for each work-item is therefore the coordinates of a pixel in the destination image.

The kernel function needs to take the following arguments:

• Destination image, __write_only image2d_t.

  This image will become the output; the kernel should write all of it.

• First Source image, __read_only image2d_t. Second Source image, __read_only image2d_t.

  These are the most recent images on each input. The kernel may read from them to generate the output, but they can’t be written to.

• Transition progress, float. This value is always between 0 and 1 inclusive.

Example programs:

• Apply dots curtain transition effect:

  __kernel void blend_images(__write_only image2d_t dst,
                             __read_only  image2d_t src1,
                             __read_only  image2d_t src2,
                             float progress)
  {
      const sampler_t sampler = (CLK_NORMALIZED_COORDS_FALSE |
                                 CLK_FILTER_LINEAR);
      int2  p = (int2)(get_global_id(0), get_global_id(1));
      float2 rp = (float2)(get_global_id(0), get_global_id(1));
      float2 dim = (float2)(get_image_dim(src1).x, get_image_dim(src1).y);
      rp = rp / dim;
  
      float2 dots = (float2)(20.0, 20.0);
      float2 center = (float2)(0,0);
      float2 unused;
  
      float4 val1 = read_imagef(src1, sampler, p);
      float4 val2 = read_imagef(src2, sampler, p);
      bool next = distance(fract(rp * dots, &unused), (float2)(0.5, 0.5)) < (progress / distance(rp, center));
  
      write_imagef(dst, p, next ? val1 : val2);
  }