Extract row data from csv file. Flutter - flutter

Question

I'm having a file containing multiple data in different rows, where in the first row is having some of the ANSI values and the other rows is having UTF-8 related values.
I was hoping to extract only the first row and decode the ANSI value with the help of the ascii.decoder and in the other rows with the help of utf-8.decoder.
I successfully did the decode when i removed the first row from the csv file manually and vice versa but how to do that programmatically?
This is what I'm trying to do
final ackFile = File(entities[i].path).openRead(); //To read the file
final ackFields = await ackFile.transform(utf8.decoder).transform(const CsvToListConverter()).toList(); //To extract it I'm getting error
//also here
final ackFile = File(entities[i].path).openRead().transform(utf8.decoder).transform(LineSplitter()).forEach((element) => print("Element is $element")); //When trying to read the csv file line by line
I'm getting an error stating as
I/flutter (22362): The supplied value (512.000000pt) will be discarded and treated as if it had not been specified.
E/flutter (22362): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: FormatException: Unexpected extension byte (at offset 82)
E/flutter (22362): #0 _Utf8Decoder.convertChunked (dart:convert-patch/convert_patch.dart:1893:7)
E/flutter (22362): #1 _Utf8ConversionSink.addSlice (dart:convert/string_conversion.dart:314:28)
E/flutter (22362): #2 _Utf8ConversionSink.add (dart:convert/string_conversion.dart:310:5)
E/flutter (22362): #3 _ConverterStreamEventSink.add (dart:convert/chunked_conversion.dart:72:18)
E/flutter (22362): #4 _SinkTransformerStreamSubscription._handleData (dart:async/stream_transformers.dart:111:24)
E/flutter (22362): #5 _rootRunUnary (dart:async/zone.dart:1436:47)
E/flutter (22362): #6 _CustomZone.runUnary (dart:async/zone.dart:1335:19)
E/flutter (22362): #7 _CustomZone.runUnaryGuarded (dart:async/zone.dart:1244:7)
E/flutter (22362): #8 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:341:11)
E/flutter (22362): #9 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:271:7)
E/flutter (22362): #10 _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:733:19)
E/flutter (22362): #11 _StreamController._add (dart:async/stream_controller.dart:607:7)
E/flutter (22362): #12 _StreamController.add (dart:async/stream_controller.dart:554:5)
E/flutter (22362): #13 _FileStream._readBlock.<anonymous closure> (dart:io/file_impl.dart:98:19)
E/flutter (22362): #14 _rootRunUnary (dart:async/zone.dart:1436:47)
E/flutter (22362): #15 _CustomZone.runUnary (dart:async/zone.dart:1335:19)
E/flutter (22362): <asynchronous suspension>
E/flutter (22362):