How to change file extension in Flutter? - dart

Question

I have to download media files from a website which returns a video URL like this:
https://scontent-dfw5-2.cdninstagram.com/vp/1cdfc59a008aa7609b5a91d7fdf58a81/5CB6F8B1/t50.12441-16/57499829_322195418440891_1171410395492073139_n.mp4?_nc_ht=scontent-dfw5-2.cdninstagram.com
I download this video file using flutter_downlaoder.
Downloaded file does not contain any extension so i have to add it myself.
I have to rename downloaded file in following format:
[username]_[timestamp].mp4
Problem is that when i download this video file without extension and add it manually by renaming from storage directory, video plays fine but when i rename programmatically it doesn't play and gives 'Video Format Error'.
I have shared my code below. How to fix this issue?
Future downloadMedia(String userName, String videoURL, String downloadPath, BuildContext context) async {
String filename = "${userName}_${DateTime.now().millisecondsSinceEpoch}";
String downloadURL = videoURL;
String taskId = await FlutterDownloader.enqueue(
url: downloadURL,
savedDir: downloadPath,
fileName: filename,
showNotification: false,
openFileFromNotification: false);
FlutterDownloader.registerCallback((id, status, progress) async {
if (progress.toInt() >= 100) {
String newFilename = "$filename.mp4";
Future.delayed(const Duration(milliseconds: 500), () {
File(downloadPath + "/" + filename)
.renameSync(downloadPath + "/" + newFilename);
});
}
});
}

Answer 1

I searched around and found that renaming video file will always mess up video codec settings, so best way is to handle it using FFMpeg.
import 'package:flutter_downloader/flutter_downloader.dart';
import 'package:flutter_ffmpeg/flutter_ffmpeg.dart';
class Download {
final FlutterFFmpeg _flutterFFmpeg = FlutterFFmpeg();
Future downloadMedia(String userName, String videoURL, String downloadPath,
BuildContext context) async {
String filename = "${userName}_${DateTime.now().millisecondsSinceEpoch}";
String filenameOriginal =
"${userName}_${DateTime.now().millisecondsSinceEpoch}";
String downloadURL = videoURL;
var started = false;
await FlutterDownloader.enqueue(
url: downloadURL,
savedDir: downloadPath,
fileName: filename,
showNotification: false,
openFileFromNotification: false);
FlutterDownloader.registerCallback((id, status, progress) async {
if (progress.toInt() >= 100) {
started = true;
var inputFile = "${downloadPath + "/" + filename}";
var outputFile = "${downloadPath + "/" + filenameOriginal}_${DateTime.now().millisecondsSinceEpoch}.mp4";
_flutterFFmpeg
.execute("-i inputFile -c copy outputFile")
.then((rc) => print("FFmpeg process exited with rc $rc"));
//Export file as Mp4 Video
}
});
}
}
Exported video file can easily be played in VLC player or MX player apps.