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• flutter_ffmpeg concat demuxer | front camera videos are upside-down

  18 avril 2021, par Gicminos

  I am currently recording multiple mp4 clips (using Flutter's camera package) and then using ffmpeg concat demuxer to create a single video :

  


  await _flutterFFmpeg.execute('-f concat -safe 0 -i ${txtFile.path} -c copy ${outputClipPath.path}');


  


  This works correctly with any video from the rear camera. When I also concat videos from the front camera, these are upside-down as it seems that ffmpeg does not detect their metadata rotation.

  


  Currently, I have manged to detect if a video is front camera or rear camera in this way :

  


  final FlutterFFprobe flutterFFprobe = FlutterFFprobe();
MediaInformation mediaInformation = await flutterFFprobe.getMediaInformation(this.path);

Map mp = mediaInformation.getAllProperties();

int rotation = mp['streams'][0]['side_data_list'][0]['rotation'];
if (rotation == 90) {
  // Video is upside down and from front-camera
}


  


  The question is, do I need to rotate the video myself prior to concat it ? If yes, what is the best way to do that with flutter_ffmpeg ?

  


  I managed to rotate the video with the following command :

  


  await _flutterFFmpeg.execute('-noautorotate -i ${this.path} -metadata:s:v rotate="0" -vf "transpose=2" ${outputClipPath.path}');


  


  But if I do that then the concat result is corrupted. How do I preserve the encoding and stream after rotation ?

  


  Thank you.

  


• How would I dynamically link FFmpeg in a C# Project for use with FFMpegCore ?

  15 octobre 2024, par liamliam

  So far, I have FFMpegCore working in my project with a ffmpeg.exe dropped into the project directory. This works, but for LGPL license compliance FFmpeg requires dynamic linking :
  
Use dynamic linking (on windows, this means linking to dlls) for linking with FFmpeg libraries..

  


  While I understand the basic concept of dynamic vs static linking, my problem is likely a misunderstanding of how .dlls work and how they apply to C# and .NET.
  
Would it be possible to compile ffmpeg into a single .dll that could be accessed by FFMpegCore cross-platform ? From what I can gather in the source, FFMpegCore looks for an ffmpeg or ffmpeg.exe file in its configuration path.

  


  Is it possible to have .NET dynamically link FFmpeg and expose it to libraries for use or is that a complete misunderstanding and would I then need a wrapper library with different capabilities ?

  


  I've attempted to find the answer in the relevant documentation, but I found none for this specific use of either library. I suspect my problem might be a fundamental misunderstanding of how these tools work and work together.
My ideal result would be using FFMpegCore with an FFmpeg.dll that works cross-platform instead of the .exe.

  


  Edit 1 : @taratect's answer and graphic sent me down a path that cleared up quite a bit about exes and dlls. .Net compiles source code down to platform agnostic Intermediate Language in the form of a .dll or .exe(completely different to C++ variants of these files), which is executed by the Common Language Runtime using a Just In Time compiler to convert that Intermediate Language to Machine Code that can be run on the specific platform .Net is installed on. C++(FFmpeg) compiles directly to platform specific Machine Code (as shown in the graphic), confusingly in the form of a .dll or .exe (on Windows). .Net can indeed load and run machine code unmanaged by Common Language Runtime, since everything is run as Machine Code by the end, however memory and other complexities must then be managed by me, which seems to be what FFMpegCore does in wrapping the executable. I might still be confused/incorrect on some of this, unmanaged code is beyond my understanding so far.
This does more or less confirm that FFMpegCore probably can't be expected to use FFmpeg in the way I hoped and a better workaround might be having the user just supply an FFmpeg source or implement a downloader as part of installation so that I don't have to redistribute it at all.

  


• How to convert images to video using FFMpeg for embedded applications ?

  19 avril 2019, par zthatch56

  I’m encoding images as video using FFmpeg using custom C code rather than linux commands because I am developing the code for an embedded system.

  I am currently following through the first dranger tutorial and the code provided in the following question.

  How to encode a video from several images generated in a C++ program without writing the separate frame images to disk ?

  I have found some "less abstract" code in the following github location.

  https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/encode_video.c

  And I plan to use it as well.

  My end goal is simply to save video on an embedded system using embedded C source code, and I am coming up the curve too slowly. So in summary my question is, Does it seem like I am following the correct path here ? I know that my system does not come with hardware for video codec conversion, which means I need to do it with software, but I am unsure if FFmpeg is even a feasible option for embedded work because I am yet to compile.

  The biggest red flag for me thus far is that FFmpeg uses dynamic memory allocation. I am unfamiliar with how to assess the amount of dynamic memory that it uses. This is very important information to me, and if anyone is familiar with the amount of memory used or how to assess it before compiling, I would greatly appreciate the input.