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FFmpeg Concatenation Command Fails in Flutter App
18 février 2024, par PetroI'm developing a Flutter application where I need to concatenate several images into a single video file using FFmpeg. Despite following the recommended practices and trying multiple variations of the FFmpeg command, all my attempts result in failure with an exit code of 1.


FFMPEG Version :
ffmpeg_kit_flutter: ^6.0.3-LTS

All of the files are present when this happens...



Environment :
Flutter app targeting Android
Using ffmpeg-kit-flutter for FFmpeg operations


Objective :
To concatenate multiple images stored in the app's file system into a video.


Code Snippet :
I'm generating a list of image paths, writing them to a file (ffmpeg_list.txt), and using that file with FFmpeg's concat demuxer. Here's a simplified version of my code :


Future<void> _createVideoFromImages() async {
 final Directory appDir = await getApplicationDocumentsDirectory();
 final Uuid uuid = Uuid();
 final String videoFileName = uuid.v4();
 final String outputPath = '${appDir.path}/$videoFileName.mp4';
 
 final Directory tempImageDir = await Directory('${appDir.path}/tempImages').create();
 final StringBuffer ffmpegInput = StringBuffer();
 int index = 0;

 for (var image in _images) {
 String newFileName = 'img${index++}${Path.extension(image.path)}'.replaceAll(' ', '_');
 final String newPath = '${tempImageDir.path}/$newFileName';
 await image.copy(newPath);
 ffmpegInput.writeln("file '$newPath'");
 }

 final String listFilePath = '${appDir.path}/ffmpeg_list.txt';
 await File(listFilePath).writeAsString(ffmpegInput.toString());

 if(await File(listFilePath).exists()) {
 String ffmpegCommand = "-v verbose -f concat -safe 0 -i $listFilePath -vsync vfr -pix_fmt yuv420p -c:v libx264 -r 30 $outputPath";
 // Additional commands tried here...
 await FFmpegKit.execute(ffmpegCommand).then((session) async {
 // Error handling code...
 });
 }
}

Result Logs:
I/flutter: file exists at /data/user/0/com.example.app/app_flutter/ffmpeg_list.txt
I/flutter: FFmpeg command: -v verbose -f concat -safe 0 -i /data/user/0/com.example.app/app_flutter/ffmpeg_list.txt -vsync vfr -pix_fmt yuv420p -c:v libx264 -r 30 /data/user/0/com.example.app/app_flutter/58fdf92b-47b0-49d1-be93-d9c95870c733.mp4
I/flutter: Failed to create video
I/flutter: FFmpeg process exited with:1
I/flutter: FFmpeg command failed with logs: ffmpeg version n6.0 Copyright (c) 2000-2023 the FFmpeg developers...
</void>

Attempts :
-Simplified the FFmpeg command by removing -vsync vfr, -pix_fmt yuv420p, and adjusting -r 30 parameters.
-Tried using the -c copy option to avoid re-encoding.
-Tested with a single image to ensure basic functionality works.
-Checked file permissions and ensured all images and the list file are accessible.


Despite these attempts, the command fails without providing specific error messages related to the command's execution. The verbose logs do not offer insights beyond the FFmpeg version and configuration.


Questions :
Are there known issues with FFmpeg's concat that might lead to such failures ?
Are there alternative approaches ?


I appreciate any insights or suggestions the community might have. Thank you !


Full code :


Future<void> _createVideoFromImages() async {
 final Directory appDir = await getApplicationDocumentsDirectory();
 final Uuid uuid = Uuid();
 final String videoFileName = uuid.v4();
 final String outputPath = '${appDir.path}/$videoFileName.mp4';
 final String singleImagePath = _images[0]!.path;

// Create a directory to store renamed images to avoid any naming conflict
 final Directory tempImageDir = await Directory('${appDir.path}/tempImages').create();

 final StringBuffer ffmpegInput = StringBuffer();
 int index = 0; // To ensure unique filenames

 for (var image in _images) {
 // Generate a new filename by replacing spaces with underscores and adding an index
 String newFileName = 'img${index++}${p.extension(image!.path)}'.replaceAll(' ', '_');
 final String newPath = '${tempImageDir.path}/$newFileName';

 // Copy and rename the original file to the new path
 await image!.copy(newPath);

 // Add the new, safely named file path to the ffmpegInput
 ffmpegInput.writeln("file '$newPath'");
 }

// Write the paths to a temporary text file for FFmpeg's concat demuxer
 final String listFilePath = '${appDir.path}/ffmpeg_list.txt';
 await File(listFilePath).writeAsString(ffmpegInput.toString());

 //check if file exists
 if(await File(listFilePath).exists()) {
 print("file exists at $listFilePath");

// Use the generated list file in the concat command
 String ffmpegCommand = "-v verbose -f concat -safe 0 -i $listFilePath -vsync vfr -pix_fmt yuv420p -c:v libx264 -r 30 $outputPath";
 String ffmpegCommand2 = "-v verbose -f concat -safe 0 -i $listFilePath -c:v libx264 $outputPath";
 String ffmpegCommand3 = "-v verbose -i $singleImagePath -frames:v 1 $outputPath";
 //print command
 print("FFmpeg command: $ffmpegCommand");


 await FFmpegKit.execute(ffmpegCommand).then((session) async {
 // Check the session for success or failure
 final returnCode = await session.getReturnCode();
 if (returnCode!.isValueSuccess()) {
 print("Video created successfully: $outputPath");
 //okay all set, now set the video to be this:
 _actual_video_file_ready_to_upload = File(outputPath);
 print ("video path is: ${outputPath}");
 } else {
 print("Failed to create video");
 print("FFmpeg process exited with:" + returnCode.toString());
 // Command failed; capture and log error details
 await session.getLogsAsString().then((logs) {
 print("FFmpeg command failed with logs: $logs");
 });
 // Handle failure, e.g., by showing an error message
 showSnackBarHelperERRORWrapLongString(context, "Failed to create video");
 }
 });

 //try command 2
 if(_actual_video_file_ready_to_upload == null) {
 await FFmpegKit.execute(ffmpegCommand2).then((session) async {
 // Check the session for success or failure
 final returnCode = await session.getReturnCode();
 if (returnCode!.isValueSuccess()) {
 print("Video created successfully: $outputPath");
 //okay all set, now set the video to be this:
 _actual_video_file_ready_to_upload = File(outputPath);
 print ("video path is: ${outputPath}");
 } else {
 print("Failed to create video");
 print("FFmpeg process exited with:" + returnCode.toString());
 // Command failed; capture and log error details
 await session.getLogsAsString().then((logs) {
 print("FFmpeg command failed with logs: $logs");
 });
 // Handle failure, e.g., by showing an error message
 showSnackBarHelperERRORWrapLongString(context, "Failed to create video");
 }
 });
 }
 //try command 3
 if(_actual_video_file_ready_to_upload == null) {
 await FFmpegKit.execute(ffmpegCommand3).then((session) async {
 // Check the session for success or failure
 final returnCode = await session.getReturnCode();
 if (returnCode!.isValueSuccess()) {
 print("Video created successfully: $outputPath");
 //okay all set, now set the video to be this:
 _actual_video_file_ready_to_upload = File(outputPath);
 print ("video path is: ${outputPath}");
 } else {
 print("Failed to create video");
 print("FFmpeg process exited with:" + returnCode.toString());
 // Command failed; capture and log error details
 await session.getLogsAsString().then((logs) {
 print("FFmpeg command failed with logs: $logs");
 });
 // Handle failure, e.g., by showing an error message
 showSnackBarHelperERRORWrapLongString(context, "Failed to create video");
 }
 });
 }
 }else{
 print("file does not exist at $listFilePath");
 }
 }
</void>

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