How to import WebPEncodeRGB to dart?

I want to encode image into webp in dart. I created libwebp.dll file (sources https://github.com/jacklicn/libwebp)

Now I have to use this library for encoding process:

import 'dart:ffi';
import 'dart:io';
import 'package:ffi/ffi.dart';
import 'package:flutter/foundation.dart';

typedef NativeEncodeFunc =
    Uint64 Function(
      Pointer<Uint8> rgb,
      Int32 width,
      Int32 height,
      Int32 stride,
      Float quality_factor,
      Pointer<Pointer<Uint8>> output,
    );

typedef DartEncodeFunc =
    int Function(
      Pointer<Uint8> rgb,
      int width,
      int height,
      int stride,
      double quality_factor,
      Pointer<Pointer<Uint8>> output,
    );

typedef NativeFreeFunc = Void Function(Pointer<Uint8>);
typedef DartFreeFunc = void Function(Pointer<Uint8>);

class WebPFFI {
  late final DynamicLibrary _lib;
  late final DartEncodeFunc _encode;
  late final DartFreeFunc _free;

  WebPFFI() {
    final path = _getLibraryPath();
    try {
      _lib = DynamicLibrary.open(path);
      _encode = _lib
          .lookup<NativeFunction<NativeEncodeFunc>>('WebPEncodeRGB')
          .asFunction();
      _free = _lib
          .lookup<NativeFunction<NativeFreeFunc>>('WebPFree')
          .asFunction();
    } catch (e) {
      throw Exception('Failed to load WebP library ($path): $e');
    }
  }

  Uint8List encode(Uint8List rgb, int width, int height, int quality) {
    // size check
    if (width <= 0 || height <= 0) {
      throw ArgumentError('Invalid dimensions: $width x $height');
    }
    if (quality < 0 || quality > 100) {
      throw ArgumentError('Quality must be between 0 and 100');
    }

    final rgbPtr = malloc<Uint8>(rgb.length);
    rgbPtr.asTypedList(rgb.length).setAll(0, rgb);
    final outputPtr = calloc<Pointer<Uint8>>();

    try {
      // WEBP_EXTERN(size_t) WebPEncodeRGB(const uint8_t* rgb,
      //                        int width, int height, int stride,
      //                        float quality_factor, uint8_t**
      final resultSize = _encode(
        rgbPtr,
        width,
        height,
        width * 3, // stride -> RGB
        quality.toDouble(),
        outputPtr,
      );

      if (resultSize == 0) {
        throw Exception('WebP encoding failed');
      }

      final result = outputPtr.value.asTypedList(resultSize);
      return Uint8List.fromList(result);
    } finally {
      if (outputPtr.value != nullptr) {
        _free(outputPtr.value);
      }
      calloc.free(outputPtr);
      malloc.free(rgbPtr);
    }
  }

  String _getLibraryPath() {
    if (Platform.isWindows) return 'windows/libwebp.dll';
    if (Platform.isLinux) return 'linux/libwebp.so';
    if (Platform.isMacOS) return 'macos/libwebp.dylib';
    if (Platform.isAndroid) return 'android/libwebp.soso';
    if (Platform.isIOS) return 'ios/libwebp.soso';
    if (kIsWeb) return 'web/libwebp.idk what should I use here';

    throw UnsupportedError('_getLibraryPath not supported for WebP');
  }
}

This function causes whole app crash without any exception: final resultSize = _encode( rgbPtr, width, height, width * 3, // stride -> RGB quality.toDouble(), outputPtr, );

_encode is not null, _lib is not null too. Where is a bug? How to encode image into webp?

Update:

1) dumpbin /EXPORTS libwebp.dll | findstr "WebPEncodeRGB"

     30   1D 00033A60 WebPEncodeRGB
     31   1E 00033AA0 WebPEncodeRGBA

2) Doesn't throw an exception:

if (_lib.providesSymbol('WebPEncodeRGB') == false) {
        throw Exception('Symbol WebPEncodeRGB not found in library');
      }