Here is a GLSL shader, that will unwarp a 'fisheye' (its not going to be perfect, since its not calibrated to any specific lens), but it should provide a decent result.

/*
Fisheye Correction - Fragment Shader
For Isadora GLSL Shader actor
*/
// ISADORA_PLUGIN_NAME("Fisheye Correction")
// ISADORA_PLUGIN_DESC("Corrects fisheye lens distortion from an input video stream to create a flatter, non-fisheye output.")
// ISADORA_FLOAT_PARAM(strength, strn, 0.0, 200.0, 100.0, "Amount of fisheye correction. Higher values remove more barrel distortion.")
uniform float strength;
// ISADORA_FLOAT_PARAM(zoom, zoom, 50.0, 200.0, 115.0, "Zooms the corrected image to hide curved black edges.")
uniform float zoom;
// ISADORA_FLOAT_PARAM(horz_center, ctrx, -100.0, 100.0, 0.0, "Horizontal center of the lens correction.")
uniform float horz_center;
// ISADORA_FLOAT_PARAM(vert_center, ctry, -100.0, 100.0, 0.0, "Vertical center of the lens correction.")
uniform float vert_center;
// ISADORA_FLOAT_PARAM(edge_softness, edge, 0.0, 20.0, 2.0, "Softens the edge where the corrected image runs outside the source.")
uniform float edge_softness;
// Built-in Isadora uniforms
uniform vec2 resolution;
uniform sampler2D tex0;
void main(void)
{
    vec2 uv = gl_TexCoord[0].xy;
    // Move coordinates so that 0,0 is the image center.
    vec2 center = vec2(0.5) + vec2(horz_center, vert_center) / 200.0;
    vec2 p = uv - center;
    // Correct for non-square aspect ratio.
    float aspect = resolution.x / resolution.y;
    p.x *= aspect;
    // Zoom after correction. Higher zoom crops the outer edges.
    p /= zoom / 100.0;
    // Distance from lens center.
    float r = length(p);
    // Barrel/fisheye correction.
    // The shader samples farther outward as pixels move from the center,
    // which visually straightens fisheye-curved lines.
    float k = strength / 100.0;
    float corrected_r = r * (1.0 + k * r * r);
    vec2 corrected_p = p;
    if (r > 0.00001) {
        corrected_p = normalize(p) * corrected_r;
    }
    // Undo aspect correction and return to texture coordinates.
    corrected_p.x /= aspect;
    vec2 sample_uv = corrected_p + center;
    // Create a soft mask so out-of-range areas fade to black.
    float soft = edge_softness / 100.0;
    float mask_x = smoothstep(0.0, soft, sample_uv.x) *
                   smoothstep(0.0, soft, 1.0 - sample_uv.x);
    float mask_y = smoothstep(0.0, soft, sample_uv.y) *
                   smoothstep(0.0, soft, 1.0 - sample_uv.y);
    float mask = mask_x * mask_y;
    // Clamp sampling to avoid texture wrapping artifacts.
    sample_uv = clamp(sample_uv, vec2(0.0), vec2(1.0));
    vec4 color = texture2D(tex0, sample_uv);
    gl_FragColor = vec4(color.rgb * mask, color.a);
}