How do I use this async function's callback parm to know when my function finished executing?

user_4838216 0
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New to flutter and async programming in general. I want to use this function:

https://pub.dev/documentation/ffmpeg_kit_flutter/latest/ffmpeg_kit/FFmpegKit/executeAsync.html

I don't understand the part that says

You must use an FFmpegSessionCompleteCallback if you want to be notified about the result.

Can someone explain how to use this as if I was a beginner programmer? Is this parameter something I can use to print a simple message to the console, like 'execution finished'?

What I've tried so far:

String test1() {
    return 'FFMPEG FINISHED';
  }

...later in the code

await FFmpegKit.executeAsync('ffmpeg -i ' + FileDir.path + currentFilename + ' ' + FileDir.path + currentOutputFilename + '.mp3', test1());

This gives an error pointing to the end of the await FFmpegKit... line: The argument type 'String' can't be assigned to the parameter type 'void Function(FFmpegSession)?'.

dart flutter ffmpeg android ios
1 Answers

The callback will be invoked when the operation completes. However, when you do

await FFmpegKit.executeAsync(..., test1());

you're not passing a callback. Instead, you're invoking your function yourself and passing the result (which fails with a type error).

You need to pass the function itself, not the result of invoking it:

await FFmpegKit.executeAsync(..., test1);

Additionally, your test1 callback has the wrong signature, and it will not do anything since it just returns a value that won't be used anywhere. You therefore need to make an additional change:

void test1(FFmpegSession session) {
  print('FFMPEG FINISHED');
}
user_1797150
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