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Merged Video Contains Inverted Clips After First Video Ends
3 février, par Nikunj AgrawalI am working on a Flutter application that merges multiple videos using
ffmpeg_kit_flutter. However, after merging, I notice that the second video (and any subsequent ones) appear inverted or rotated in the final output.

Issue Details :


- 

- The first video appears normal.
- The videos can be recorded using both front and back cameras.
- The second (and later) videos are flipped or rotated upside down.
- This happens after merging using
ffmpeg_kit_flutter.










Question :
How can I correctly merge multiple videos in Flutter without rotation issues ? Is there a way to normalize video orientation before merging using
ffmpeg_kit_flutter?

Any help would be appreciated ! 🚀


Code :


import 'dart:io';
import 'dart:math';

import 'package:camera/camera.dart';
import 'package:ffmpeg_kit_flutter/ffmpeg_kit.dart';
import 'package:ffmpeg_kit_flutter/return_code.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:record/record.dart';
import 'package:videotest/video_player.dart';

class MergeVideoRecording extends StatefulWidget {
 const MergeVideoRecording({super.key});

 @override
 State<mergevideorecording> createState() => _MergeVideoRecordingState();
}

class _MergeVideoRecordingState extends State<mergevideorecording> {
 CameraController? _cameraController;
 final AudioRecorder _audioRecorder = AudioRecorder();

 bool _isRecording = false;
 String? _videoPath;
 String? _audioPath;
 List<cameradescription> _cameras = [];
 int _currentCameraIndex = 0;
 final List<string> _recordedVideos = [];

 @override
 Widget build(BuildContext context) {
 return Scaffold(
 body: Column(
 mainAxisAlignment: MainAxisAlignment.center,
 children: [
 _cameraController != null && _cameraController!.value.isInitialized
 ? SizedBox(
 width: MediaQuery.of(context).size.width * 0.4,
 height: MediaQuery.of(context).size.height * 0.3,
 child: Stack(
 children: [
 ClipRRect(
 borderRadius: BorderRadius.circular(16),
 child: SizedBox(
 width: MediaQuery.of(context).size.width * 0.4,
 height: MediaQuery.of(context).size.height * 0.3,
 child: Transform(
 alignment: Alignment.center,
 transform:
 _cameras[_currentCameraIndex].lensDirection ==
 CameraLensDirection.front
 ? Matrix4.rotationY(pi)
 : Matrix4.identity(),
 child: CameraPreview(_cameraController!),
 ),
 ),
 ),
 Align(
 alignment: Alignment.topRight,
 child: InkWell(
 onTap: _switchCamera,
 child: const Padding(
 padding: EdgeInsets.all(8.0),
 child: CircleAvatar(
 radius: 18,
 backgroundColor: Colors.white,
 child: Icon(
 Icons.flip_camera_android,
 color: Colors.black,
 ),
 ),
 ),
 ),
 ),
 ],
 ),
 )
 : const CircularProgressIndicator(),
 const SizedBox(height: 16),
 Row(
 mainAxisAlignment: MainAxisAlignment.center,
 children: [
 FloatingActionButton(
 heroTag: 'record_button',
 onPressed: _toggleRecording,
 child: Icon(
 _isRecording ? Icons.stop : Icons.video_camera_back,
 ),
 ),
 const SizedBox(
 width: 50,
 ),
 FloatingActionButton(
 heroTag: 'merge_button',
 onPressed: _mergeVideos,
 child: const Icon(
 Icons.merge,
 ),
 ),
 ],
 ),
 if (!_isRecording)
 ListView.builder(
 shrinkWrap: true,
 itemCount: _recordedVideos.length,
 itemBuilder: (context, index) => InkWell(
 onTap: () {
 Navigator.push(
 context,
 MaterialPageRoute(
 builder: (context) => VideoPlayerScreen(
 videoPath: _recordedVideos[index],
 ),
 ),
 );
 },
 child: ListTile(
 title: Text('Video ${index + 1}'),
 subtitle: Text('Path ${_recordedVideos[index]}'),
 trailing: const Icon(Icons.play_arrow),
 ),
 ),
 ),
 ],
 ),
 );
 }

 @override
 void dispose() {
 _cameraController?.dispose();
 _audioRecorder.dispose();
 super.dispose();
 }

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

 Future<void> _initializeCameraController(CameraDescription camera) async {
 _cameraController = CameraController(
 camera,
 ResolutionPreset.high,
 enableAudio: true,
 imageFormatGroup: ImageFormatGroup.yuv420, // Add this line
 );

 await _cameraController!.initialize();
 await _cameraController!.setExposureMode(ExposureMode.auto);
 await _cameraController!.setFocusMode(FocusMode.auto);
 setState(() {});
 }

 Future<void> _initializeDevices() async {
 final cameraStatus = await Permission.camera.request();
 final micStatus = await Permission.microphone.request();

 if (!cameraStatus.isGranted || !micStatus.isGranted) {
 _showError('Camera and microphone permissions required');
 return;
 }

 _cameras = await availableCameras();
 if (_cameras.isNotEmpty) {
 final frontCameraIndex = _cameras.indexWhere(
 (camera) => camera.lensDirection == CameraLensDirection.front);
 _currentCameraIndex = frontCameraIndex != -1 ? frontCameraIndex : 0;
 await _initializeCameraController(_cameras[_currentCameraIndex]);
 }
 }

 // Merge video
 Future<void> _mergeVideos() async {
 if (_recordedVideos.isEmpty) {
 _showError('No videos to merge');
 return;
 }

 try {
 // Debug logging
 print('Starting merge process');
 print('Number of videos to merge: ${_recordedVideos.length}');
 for (var i = 0; i < _recordedVideos.length; i++) {
 final file = File(_recordedVideos[i]);
 final exists = await file.exists();
 final size = exists ? await file.length() : 0;
 print('Video $i: ${_recordedVideos[i]}');
 print('Exists: $exists, Size: $size bytes');
 }

 final Directory appDir = await getApplicationDocumentsDirectory();
 final String outputPath =
 '${appDir.path}/merged_${DateTime.now().millisecondsSinceEpoch}.mp4';
 final String listFilePath = '${appDir.path}/list.txt';

 print('Output path: $outputPath');
 print('List file path: $listFilePath');

 // Create and verify list file
 final listFile = File(listFilePath);
 final fileContent = _recordedVideos
 .map((path) => "file '${path.replaceAll("'", "'\\''")}'")
 .join('\n');
 await listFile.writeAsString(fileContent);

 print('List file content:');
 print(await listFile.readAsString());

 // Simpler FFmpeg command for testing
 final command = '''
 -f concat
 -safe 0
 -i "$listFilePath"
 -c copy
 -y
 "$outputPath"
 '''
 .trim()
 .replaceAll('\n', ' ');

 print('Executing FFmpeg command: $command');

 final session = await FFmpegKit.execute(command);
 final returnCode = await session.getReturnCode();
 final logs = await session.getAllLogsAsString();
 final failStackTrace = await session.getFailStackTrace();

 print('FFmpeg return code: ${returnCode?.getValue() ?? "null"}');
 print('FFmpeg logs: $logs');
 if (failStackTrace != null) {
 print('FFmpeg fail stack trace: $failStackTrace');
 }

 if (ReturnCode.isSuccess(returnCode)) {
 final outputFile = File(outputPath);
 final outputExists = await outputFile.exists();
 final outputSize = outputExists ? await outputFile.length() : 0;

 print('Output file exists: $outputExists');
 print('Output file size: $outputSize bytes');

 if (outputExists && outputSize > 0) {
 setState(() => _recordedVideos.add(outputPath));
 _showSuccess('Videos merged successfully');
 } else {
 _showError('Merged file is empty or not created');
 }
 } else {
 _showError('Failed to merge videos. Check logs for details.');
 }

 // Clean up
 try {
 await listFile.delete();
 print('List file cleaned up successfully');
 } catch (e) {
 print('Failed to delete list file: $e');
 }
 } catch (e, s) {
 print('Error during merge: $e');
 print('Stack trace: $s');
 _showError('Error merging videos: ${e.toString()}');
 }
 }

 void _showError(String message) {
 ScaffoldMessenger.of(context).showSnackBar(
 SnackBar(content: Text(message), backgroundColor: Colors.red),
 );
 }

 void _showSuccess(String message) {
 ScaffoldMessenger.of(context).showSnackBar(
 SnackBar(content: Text(message), backgroundColor: Colors.green),
 );
 }

 Future<void> _startAudioRecording() async {
 try {
 final Directory tempDir = await getTemporaryDirectory();
 final audioPath = '${tempDir.path}/recording.wav';
 await _audioRecorder.start(const RecordConfig(), path: audioPath);
 setState(() => _isRecording = true);
 } catch (e) {
 _showError('Recording start error: $e');
 }
 }

 Future<void> _startVideoRecording() async {
 try {
 await _cameraController!.startVideoRecording();
 setState(() => _isRecording = true);
 } catch (e) {
 _showError('Recording start error: $e');
 }
 }

 Future<void> _stopAndSaveAudioRecording() async {
 _audioPath = await _audioRecorder.stop();
 if (_audioPath != null) {
 final Directory appDir = await getApplicationDocumentsDirectory();
 final timestamp = DateTime.now().millisecondsSinceEpoch;
 final String audioFileName = 'audio_$timestamp.wav';
 await File(_audioPath!).copy('${appDir.path}/$audioFileName');
 _showSuccess('Saved: $audioFileName');
 }
 }

 Future<void> _stopAndSaveVideoRecording() async {
 try {
 final video = await _cameraController!.stopVideoRecording();
 _videoPath = video.path;

 if (_videoPath != null) {
 final Directory appDir = await getApplicationDocumentsDirectory();
 final timestamp = DateTime.now().millisecondsSinceEpoch;
 final String videoFileName = 'video_$timestamp.mp4';
 final savedVideoPath = '${appDir.path}/$videoFileName';
 await File(_videoPath!).copy(savedVideoPath);

 setState(() {
 _recordedVideos.add(savedVideoPath);
 _isRecording = false;
 });

 _showSuccess('Saved: $videoFileName');
 }
 } catch (e) {
 _showError('Recording stop error: $e');
 }
 }

 Future<void> _switchCamera() async {
 if (_cameras.length <= 1) return;

 if (_isRecording) {
 await _stopAndSaveVideoRecording();
 _currentCameraIndex = (_currentCameraIndex + 1) % _cameras.length;
 await _initializeCameraController(_cameras[_currentCameraIndex]);
 await _startVideoRecording();
 } else {
 _currentCameraIndex = (_currentCameraIndex + 1) % _cameras.length;
 await _initializeCameraController(_cameras[_currentCameraIndex]);
 }
 }

 Future<void> _toggleRecording() async {
 if (_cameraController == null) return;

 if (_isRecording) {
 await _stopAndSaveVideoRecording();
 await _stopAndSaveAudioRecording();
 } else {
 _startVideoRecording();
 _startAudioRecording();
 setState(() => _recordedVideos.clear());
 }
 }
}
</void></void></void></void></void></void></void></void></void></string></cameradescription></mergevideorecording></mergevideorecording>

-
How to convert a video to match an existing video (codec, fps, bitrate, height, width, etc.) ? [duplicate]
30 octobre 2020, par Mahdi SahebI have a video file and can see the info using
ffmpeg -i video.mp4. The question is how to use this data to encode another video file to match with this ?

-
How to use ffmpeg to extracted every nth frame from a video to generate a shorter new video ? [duplicate]
12 octobre 2022, par J.WFor example, a video length is 60 seconds with 25 FPS, there are 25 * 60 = 1500 frames.
How to extract the 1st frame every 5 frames, i.e., for the first second's 25 frames, need to extract the 5 frames at 1st, 6th, 11th, 16th and 21st, so the result new video would have 300 frames in total, and at the same time keep the same FPS (or increase FPS) to make the new video shorter, for example :


- 

- to keep the result video to be 25 FPS (same as original video), the video length is 12 seconds ; or
- to make the result video to be 30 FPS, the video length is 10 seconds






Note : the answer in the comment of this similar question solved my question :


ffmpeg -an -i in.mp4 -vf framestep=5,setpts=N/25/TB -r 25 out.mp4


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