You’re about to enhance your Flutter projects and become a pro at mixing audio and video. Let’s start this coding journey together and open up a whole new world of possibilities. Get ready to blend, tweak, and craft with FFmpeg in Flutter—because your digital ideas deserve to look and sound amazing!

We will start setting up our project by adding packages that we will need to merge MP3 and MP4 files using FFmpeg.
ffmpeg_kit_flutter:- This package will help us run FFmpeg commands in Flutter, using which we will merge MP3 with MP4.
path_provider:- Path Provider will help us get directory paths using which we can fetch the audio and video files and also save our output file.
permission_handler:- We will be needing this package so that we can get permission to read or write user’s files.

pubspec.yaml :-

dependencies:
  flutter:
    sdk: flutter
  ffmpeg_kit_flutter: ^x.x.x  # Replace with the latest version
  path_provider: ^x.x.x  # Replace with the latest version
  permission_handler: ^x.x.x  # Replace with the latest version

Now we can start coding by making three functions that will help us merge audio and video files

First of all, we will request storage permission from the user so that we can access their mp3 and mp4 files

  PermissionStatus _permissionStatus = PermissionStatus.undetermined;

  @override
  void initState() {
    super.initState();
    _requestStoragePermission();
  }

  Future<void> _requestStoragePermission() async {
    final status = await Permission.storage.request();
    setState(() {
      _permissionStatus = status;
    });
  }

Then we will get the path where we want to get our mp3 and mp4 files and save our output.mp4 file

  Future<String> _getAudioFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/audio.mp3'; // Replace with your audio file path
  }

  Future<String> _getVideoFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/video.mp4'; // Replace with your video file path
  }

  Future<String> _getOutputFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/output.mp4'; // Replace with your desired output file path
  }

Now we will be coding the main function where our video and the audio will be merged using FFmpeg

  Future<void> _mergeAudioAndVideo() async {
    if (_permissionStatus != PermissionStatus.granted) {
      print('Storage permission not granted.');
      return;
    }

    final audioPath = await _getAudioFilePath();
    final videoPath = await _getVideoFilePath();
    final outputPath = await _getOutputFilePath();

    final command =
        '-i $videoPath -i $audioPath -c:v copy -c:a aac -strict experimental $outputPath';

    final executionId = await FFmpegKit.executeAsync(command);
    final returnCode = await FFmpegKitConfig.getLastReturnCode();

    if (returnCode == ReturnCode.SUCCESS) {
      print('Merge successful');
    } else {
      print('Merge failed');
    }
  }

Now let’s create a basic UI using which the user will trigger the function and the merging will start

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Audio and Video Merge Demo'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: _mergeAudioAndVideo,
          child: Text('Merge Audio and Video'),
        ),
      ),
    );
  }

This is it! You merged an audio file and a video file using Flutter and FFmpeg.

You can find the whole code here:

import 'package:flutter/material.dart';
import 'package:ffmpeg_kit_flutter/ffmpeg_kit.dart';
import 'package:path_provider/path_provider.dart';
import 'package:permission_handler/permission_handler.dart';

class AudioVideoMergeDemo extends StatefulWidget {
  @override
  _AudioVideoMergeDemoState createState() => _AudioVideoMergeDemoState();
}

class _AudioVideoMergeDemoState extends State<AudioVideoMergeDemo> {
  PermissionStatus _permissionStatus = PermissionStatus.undetermined;

  @override
  void initState() {
    super.initState();
    _requestStoragePermission();
  }

  Future<void> _requestStoragePermission() async {
    final status = await Permission.storage.request();
    setState(() {
      _permissionStatus = status;
    });
  }

  Future<void> _mergeAudioAndVideo() async {
    if (_permissionStatus != PermissionStatus.granted) {
      print('Storage permission not granted.');
      return;
    }

    final audioPath = await _getAudioFilePath();
    final videoPath = await _getVideoFilePath();
    final outputPath = await _getOutputFilePath();

    final command =
        '-i $videoPath -i $audioPath -c:v copy -c:a aac -strict experimental $outputPath';

    final executionId = await FFmpegKit.executeAsync(command);
    final returnCode = await FFmpegKitConfig.getLastReturnCode();

    if (returnCode == ReturnCode.SUCCESS) {
      print('Merge successful');
    } else {
      print('Merge failed');
    }
  }

  Future<String> _getAudioFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/audio.mp3'; // Replace with your audio file path
  }

  Future<String> _getVideoFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/video.mp4'; // Replace with your video file path
  }

  Future<String> _getOutputFilePath() async {
    final directory = await getTemporaryDirectory();
    return '${directory.path}/output.mp4'; // Replace with your desired output file path
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Audio and Video Merge Demo'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: _mergeAudioAndVideo,
          child: Text('Merge Audio and Video'),
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: AudioVideoMergeDemo(),
  ));
}