How to convert n numbers of images into a video slideshow with putting some transition on each images with flutter_ffmpeg?

Question

I'm trying to convert images into a video slideshow with some transition. I have used flutter_ffmpeg plugin , with this plugin I have created with only 3 images but I want to add n numbers of images but couldn't able to find solutions for it. I tried to add more images but it throws error.

I'm gonna add some piece of code below :

1. Instance of FlutterFFmpeg

  final FlutterFFmpeg _flutterFFmpeg = FlutterFFmpeg(); 

2. Picking multiple images from the gallery and applying command to convert images into a video

void mergeImageVideo() async {
    final ImagePicker picker = ImagePicker();
    final images = await picker.pickMultiImage();

    var im1 = images[0].path;

    var im2 = images[1].path;

    var im3 = images[2].path;

   //-shortest
    openLoadingDialog(context, "Creating video");
    generateFilePath("ImageVideoMerge").then((outputFile) {
      var backgroundColor = 'FFF44336';

      String ffmpegCommand = VideoUtil.generateImagesToVideoScript(
          im1, im2, im3, outputFile, 'mpeg4', '', backgroundColor);

      print("ffmpegCommand==> $ffmpegCommand");
      _flutterFFmpeg.execute(ffmpegCommand).then((v) {
        if (v == 0) {
          var file = File(outputFile);
          Navigator.pop(context);
          showSnackBar(context, "Images Added Successfully", Colors.black);
          updateVideoPlayer(file);
        } else {
          Navigator.pop(context);
        }
      }).then((executionId) {
      });
    });
  }

method to get ffmpeg command (images into video with scale transition)

static String generateImagesToVideoScript(
      String image1Path,
      String image2Path,
      String image3Path,
      String videoFilePath,
      String videoCodec,
      String customOptions,
      String backgroundColor
      ) {

    // ignore: prefer_interpolation_to_compose_strings
     return "-hide_banner -y -loop 1 -i '" +
        image1Path +
        "' " +
        "-loop   1 -i \"" +
        image2Path +
        "\" " +
        "-loop 1   -i \"" +
        image3Path +
        "\" " +
        "-filter_complex " +
        "\" " +
        "[0:v]setpts=PTS-STARTPTS,scale=w=640:h=424,setsar=sar=1/1,split=2[stream1out1][stream1out2];" +
        "[1:v]setpts=PTS-STARTPTS,scale=w=640:h=424,setsar=sar=1/1,split=2[stream2out1][stream2out2];" +
        "[2:v]setpts=PTS-STARTPTS,scale=w=640:h=424,setsar=sar=1/1,split=2[stream3out1][stream3out2];" +
        "[stream1out1]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=3,select=lte(n\\,90)[stream1overlaid];" +
        "[stream1out2]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=1,select=lte(n\\,30)[stream1ending];" +
        "[stream2out1]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=2,select=lte(n\\,60)[stream2overlaid];" +
        "[stream2out2]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=1,select=lte(n\\,30),split=2[stream2starting][stream2ending];" +
        "[stream3out1]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=2,select=lte(n\\,60)[stream3overlaid];" +
        "[stream3out2]pad=width=640:height=427:x=(640-iw)/2:y=(427-ih)/2:color=#$backgroundColor,trim=duration=1,select=lte(n\\,30)[stream3starting];" +
        "[stream2starting][stream1ending]blend=all_expr='if(gte(X,(W/2)*T/1)*lte(X,W-(W/2)*T/1),B,A)':shortest=1[stream2blended];" +
        "[stream3starting][stream2ending]blend=all_expr='if(gte(X,(W/2)*T/1)*lte(X,W-(W/2)*T/1),B,A)':shortest=1[stream3blended];" +
        "[stream1overlaid][stream2blended][stream2overlaid][stream3blended][stream3overlaid]concat=n=5:v=1:a=0,scale=w=640:h=424,format=yuv420p[video]\"" +
        " -map [video] -vsync 2 -async 1 " +
        customOptions +
        "-c:v " +
        videoCodec +
        " -r 30 " +
        videoFilePath;
  }