fix pixel scale

README.md

@@ -2,10 +2,18 @@
 
 Shaders for Avidemux with OpenGL support
 
-## gopro_8:7 - Fisheye removal for GoPro 11+, 8:7 ratio, 60fps, HyperSmooth off
+## GoPro fisheye removal
+
+![Sample image](https://blog.rozk.net/wp-content/uploads/2025/07/compare.png)
+
+### gopro_8:7 - Fisheye removal for GoPro 11+, 8:7 ratio, 60fps, HyperSmooth off
+
 - unfish_gopro_8:7.glsl  
 Shader for fisheye removal
 
+- preset_gopro_8:7_4K_youtube.py  
+Preset for mp4, 4K, high bitrate
+
 - preset_gopro_8:7_4K_2160p.py  
 Preset for mp4, 4K, constant bitrate
 
@@ -15,17 +23,21 @@ Preset for mp4, FullHD, constant bitrate
 - preset_gopro_8:7_HD_720p.py  
 Preset for mp4, HD, constant bitrate
 
-- preset_gopro_8:7_QHD_540p.py  
-Preset for mp4, QHD, constant bitrate
-
 - compute_gopro_8:7.py  
 Script to compute output FOV and frame widening
 
 ### Installation for BSD/GNU-Linux systems:
-- Copy the presets to ~/.avidemux6/custom/
+
+- Copy the presets to ~/.avidemux6/custom/ or ~/.local/share/avidemux6/custom/
 - Copy the shader to /opt/rk/avidemux/ (or edit the preset to set the path)  
 
 Or just run the script install_gopro_8:7.sh
-_For commercial OS's, figure out the paths yourself :)_
+
+_For commercial OS's, figure out the paths yourself, then edit the presets to fix the path to the .glsl file_
+
 ### Usage:
-Load and edit video(s), select "Custom/preset_gopro_8:7_..." in the menu and save the video.
+
+- Load and edit video(s)
+- Select "Custom/preset_gopro..." in the menu
+- Add filters
+- Save the video

gopro_8:7/compute_gopro_8:7.py

@@ -9,6 +9,7 @@ import math
 
 frame_width = 8
 frame_height = 7
+input_ratio = frame_width / frame_height
 
 input_vertical_fov = 108.0
 input_diagonal_fov = 156.0
@@ -20,17 +21,16 @@ output_horizontal_length = math.sqrt((input_diagonal_length ** 2) / (input_verti
 output_diagonal_length = math.hypot(output_horizontal_length, input_vertical_length)
 output_diagonal_fov = math.degrees(math.atan(output_diagonal_length)) * 2.0
 
-output_ratio = output_horizontal_length / input_vertical_length
+output_ratio = 1.0 / (output_horizontal_length / input_vertical_length)
 
 print("Output FOV   = %f" % output_diagonal_fov)
 print("Output Ratio = %f" % output_ratio)
 print("= Resolutions =====================")
 
 def width_rounded_8(height):
-    width = int(round(height * output_ratio))
+    width = int(round(height * input_ratio))
     return ((width + 4) // 8) * 8
 
-print("QHD            = %i x 540" % width_rounded_8(540))
 print("HD             = %i x 720" % width_rounded_8(720))
 print("Full HD        = %i x 1080" % width_rounded_8(1080))
 print("4K             = %i x 2160" % width_rounded_8(2160))

gopro_8:7/preset_gopro_8:7_4K_2160p.py

@@ -91,9 +91,9 @@ adm.addVideoFilter(
     "shaderFile=/opt/rk/avidemux/unfish_gopro_8:7.glsl")
 adm.addVideoFilter(
     "swscale",
-    "width=3312",
+    "width=2472",
     "height=2160",
-    "algo=1",
+    "algo=2",
     "sourceAR=0",
     "targetAR=0",
     "lockAR=False",

gopro_8:7/preset_gopro_8:7_4K_youtube.py

@@ -1,12 +1,12 @@
 #PY  <- Needed to identify #
 # RozK
-# Custom preset for GoPro, 8:7 ratio, without hypersmooth, output widened scaled to QHD (540p)
+# Custom preset for GoPro, 8:7 ratio, without hypersmooth, output widened scaled to 4K (2160p), high bitrate
 
 adm = Avidemux()
 adm.videoCodec(
     "x264",
     "useAdvancedConfiguration=False",
-    "general.params=CBR=8192",
+    "general.params=CBR=65536",
     "general.threads=0",
     "general.preset=slow",
     "general.tuning=film",
@@ -91,9 +91,9 @@ adm.addVideoFilter(
     "shaderFile=/opt/rk/avidemux/unfish_gopro_8:7.glsl")
 adm.addVideoFilter(
     "swscale",
-    "width=832",
+    "width=2472",
-    "height=540",
+    "height=2160",
-    "algo=1",
+    "algo=2",
     "sourceAR=0",
     "targetAR=0",
     "lockAR=False",

gopro_8:7/preset_gopro_8:7_FullHD_1080p.py

@@ -91,9 +91,9 @@ adm.addVideoFilter(
     "shaderFile=/opt/rk/avidemux/unfish_gopro_8:7.glsl")
 adm.addVideoFilter(
     "swscale",
-    "width=1656",
+    "width=1232",
     "height=1080",
-    "algo=1",
+    "algo=2",
     "sourceAR=0",
     "targetAR=0",
     "lockAR=False",

gopro_8:7/preset_gopro_8:7_HD_720p.py

@@ -91,9 +91,9 @@ adm.addVideoFilter(
     "shaderFile=/opt/rk/avidemux/unfish_gopro_8:7.glsl")
 adm.addVideoFilter(
     "swscale",
-    "width=1104",
+    "width=824",
     "height=720",
-    "algo=1",
+    "algo=2",
     "sourceAR=0",
     "targetAR=0",
     "lockAR=False",

gopro_8:7/unfish_gopro_8:7.glsl

@@ -5,32 +5,61 @@
 
 #extension GL_ARB_texture_rectangle: enable
 
+// TODO: investigate
+// precision highp float;
+
+// uniforms
 uniform sampler2DRect myTextureY;
 uniform sampler2DRect myTextureU;
 uniform sampler2DRect myTextureV;
 uniform vec2 myResolution;
 uniform float pts;
 
-const vec2 half_pixel = vec2(0.5, 0.5);
+// parameters
-
 const float input_fov = 156.0;
-const float output_fov = 119.789529;
+const float output_fov = 124.45;
+const vec2 pixel_scale = vec2(0.652485, 1.0);
+const int subsampling = 4;
 
-vec2 unfish(vec2 coord) {
+// subsampling constants
-    float diameter = sqrt(dot(myResolution, myResolution));
+const float substep = 1.0 / float(subsampling);
-    vec2 center = myResolution * 0.5;
+const float substart = substep * 0.5 - 0.5;
-    vec2 position = coord - center;
+const float subscale = 1.0 / float(subsampling * subsampling);
-    float input_distance = length(position);
+
-    float input_foc = diameter / radians(input_fov);
+// variables
-    float output_foc = diameter / (2.0 * tan(radians(output_fov) * 0.5));
+vec2 center;
-    return center + position * (input_foc * atan(input_distance / output_foc) / input_distance);
+float diameter;
+float input_len;
+float inv_output_len;
+
+vec4 unfish(const in vec2 coord) {
+    float len = max(0.001, length(coord));
+    vec2 y_coord = center + coord * ((input_len / len) * atan(len * inv_output_len));
+    vec2 uv_coord = y_coord * 0.5;
+    return vec4(
+        texture2DRect(myTextureY, y_coord).r,
+        texture2DRect(myTextureU, uv_coord).r,
+        texture2DRect(myTextureV, uv_coord).r,
+        1.0
+    );
 }
 
 void main() {
-    vec2 y_coord = unfish(gl_TexCoord[0].xy + half_pixel);
+    center = myResolution * 0.5;
-    vec2 uv_coord = y_coord * 0.5;
+    diameter = length(myResolution);
-    vec4 y = texture2DRect(myTextureY, y_coord);
+    input_len = diameter / radians(input_fov);
-    vec4 u = texture2DRect(myTextureU, uv_coord);
+    inv_output_len = (2.0 * tan(radians(output_fov * 0.5))) / diameter;
-    vec4 v = texture2DRect(myTextureV, uv_coord);
+
-    gl_FragColor = vec4(y.r, u.r, v.r, 1.0);
+    vec2 coord = gl_TexCoord[0].xy - center;
+    vec4 pixel = vec4(0.0, 0.0, 0.0, 0.0);
+
+    float x, y = substart;
+    for (int column = 0; column < subsampling; column++, y += substep) {
+        x = substart;
+        for (int row = 0; row < subsampling; row++, x += substep) {
+            pixel += unfish((coord + vec2(x, y)) * pixel_scale);
+        }
+    }
+
+    gl_FragColor = pixel * subscale;
 }

install_gopro_8:7.sh

@@ -1,6 +1,18 @@
 #!/bin/sh
 # RozK
-rm -f ~/.avidemux6/custom/preset_gopro_*
+
-cp gopro_8:7/preset_gopro_* ~/.avidemux6/custom/
+if [ -d ~/.local/share/avidemux6 ]; then
-sudo mkdir -p /opt/rk
+  mkdir -p ~/.local/share/avidemux6/custom
-sudo cp gopro_8:7/unfish_gopro_8:7.glsl /opt/rk/
+  rm -f ~/.local/share/avidemux6/custom/preset_gopro*
+  cp gopro_8:7/preset_gopro* ~/.local/share/avidemux6/custom/
+fi
+
+if [ -d ~/.avidemux6 ]; then
+  mkdir -p ~/.avidemux6/custom
+  rm -f ~/.avidemux6/custom/preset_gopro*
+  cp gopro_8:7/preset_gopro* ~/.avidemux6/custom/
+fi
+
+sudo mkdir -p /opt/rk/avidemux
+sudo rm -f /opt/rk/avidemux/*
+sudo cp gopro_8:7/unfish_gopro_8:7.glsl /opt/rk/avidemux