Never have those width/height not divisible by 2 or padding dimensions are lower than size errors anymore. script is in dart you can ask ai to convert.

ffmepg_scale_video.dart

import 'dart:convert';
import 'dart:io';
import 'dart:math';

String generateScaleCommand(
    int inputWidth, int inputHeight, int originalWidth, int originalHeight) {
  final aspectRatio = originalWidth / originalHeight;

  bool fitToWidth = inputWidth > inputHeight;

  String filter = "";

  if (fitToWidth) {
    var iw = (inputHeight * aspectRatio).toInt();
    var ih = inputHeight;

    // clamp iw and ih to the inputwidth and inputheight but keep the ratio and divide by 2
    if (iw > inputWidth || ih > inputHeight) {
      final newSize =
          resizeBoxWithRatio(Size(iw, ih), Size(inputWidth, inputHeight));

      iw = newSize.width.toInt();
      ih = newSize.height.toInt();
    }

    iw -= (iw % 2);
    ih -= (ih % 2);

    filter =
        "scale=$iw:$ih,pad=$inputWidth:$inputHeight:($inputWidth-iw)/2:($inputHeight-ih)/2";
  } else {
    var iw = inputWidth;
    var ih = (inputWidth / aspectRatio).toInt();

    iw -= (iw % 2);
    ih -= (ih % 2);

    if (iw > inputWidth || ih > inputHeight) {
      final newSize =
          resizeBoxWithRatio(Size(iw, ih), Size(inputWidth, inputHeight));

      iw = newSize.width.toInt();
      ih = newSize.height.toInt();
    }

    filter =
        "scale=$iw:$ih,pad=$inputWidth:$inputHeight:($inputWidth-iw)/2:($inputHeight-ih)/2";
  }

  return filter;
}

class Size {
  num width;
  num height;
  Size(this.width, this.height);
}

Size resizeBoxWithRatio(Size originalSize, Size maxSize) {
  final maxWidth = maxSize.width;
  final maxHeight = maxSize.height;

  final originalWidth = originalSize.width;
  final originalHeight = originalSize.height;
  // Calculate the scale factors for width and height
  double scaleWidth = maxWidth / originalWidth;
  double scaleHeight = maxHeight / originalHeight;

  // Use the smaller scale factor to ensure the box fits within the maximum dimensions
  double scale = min(scaleWidth, scaleHeight);

  // Calculate the new dimensions
  double newWidth = (originalWidth * scale);
  double newHeight = (originalHeight * scale);

  return Size(newWidth, newHeight);
}

void main() async {
  String inputPath = "../trailer.mp4";

  // these are the original dimensions of the video file
  const int originalWidth = 1920; 
  const int originalHeight = 1080;

  int inputWidth = 500; // Replace with actual input width
  int inputHeight = 600; // Replace with actual input height

  String ffmpegCommand = generateScaleCommand(
    inputWidth,
    inputHeight,
    originalWidth,
    originalHeight,
  );

  print('FFmpeg Command: $ffmpegCommand');

  final process = await Process.start("ffmpeg", [
    "-i",
    inputPath,
    "-y",
    "-ss",
    "00:00:10.00",
    "-t",
    "00:00:20.00",
    "-vf",
    ffmpegCommand,
    "-c:v",
    "libx264",
    "../output2.mp4",
  ]);

  process.stdout.transform(utf8.decoder).listen((event) {
    print(event);
  });

  process.stderr.transform(utf8.decoder).listen((event) {
    print(event);
  });

  print(await process.exitCode);
}