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• How to "stream" images to ffmpeg to construct a video in .NET 6

  13 septembre 2021, par alkasel

  I'm using FFMPEG command line tool to create a video. As of now I retrive images from memory, but I'd like to avoid writing them to memory in first place and feed FFMPEG directly from memory.

  


  I tried accord-framework.net and it works very well, but now I've switched to .NET 6 and it is not supported (the functionality I used is based on AForge.Video.FFMPEG, an archived project not supporting recent frameworks).

  


  Now as I understand it is possible to have FFMPEG to work on streams instead of images saved on disk. In this post there is a very nice example of doing it in Python.

  


  However I don't know how to do this on .NET 6 using System.Diagnostics.Process : From this post I undestand that I could have FFMPEG take images from standard input using the syntax

  


  -i -


  


  The problem is that I cannot write on standard input before the System.IO.Process (cmd.exe ... \C ffmpeg.exe .... ) has started (I get System.InvalidOperationException : "StandardIn has not been redirected"). However, as soon as such process start, since it find standard input empty, it ends immediately, so I cannot make it in time to fill standard input.

  


  My code looks like this :

  


          MemoryStream memStream = new MemoryStream();

        // Data acquisition
        [...]
        bitmap.Save(memStream, System.Drawing.Imaging.ImageFormat.Bmp);
        [...]

        string ffmpegArgument = "/C ffmpeg.exe -y -i - -c:v libx264 -crf 12 -pix_fmt yuv420p -c:a libvo_aacenc -b:a 128k [...];

        Process cmd = new Process();
        cmd.StartInfo.FileName = "cmd.exe";
        cmd.StartInfo.Arguments = ffmpegArgument;
        cmd.StartInfo.UseShellExecute = false;
        cmd.StartInfo.RedirectStandardInput = true;
        cmd.Start();
        cmd.StandardInput.Write(memStream);


  


  Thanks to everyone who will answer.

  


• avformat/matroskaenc : Write data directly into dynamic buffers

  26 novembre 2019, par Andreas Rheinhardt

  avformat/matroskaenc : Write data directly into dynamic buffers
  This avoids copying the data in small chunks (1024B) into
  
  the dynamic buffer's small buffer before finally writing them
  
  into the "big" buffer.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/matroskaenc.c

• Write empty packets into avi file ffmpeg

  26 avril 2022, par hagor

  A task :
I have a trusted video event detector. I trust to my event detector for 100% and I want to write an uncompressed frame to my avi containter only if my event detector produces "true" result.
For frames, when my event detector is producing "false" I would like to write an empty packet because I want to know that there was a frame without event happening.
Is it possible to keep AVI file alive ? Or do I need to write my own player in this case ?

  


  Another option is to calculate timestamps manually and set dts/pts to that calculated time.
Drawback : I will need to recalculate timestamps to understand how many frames were between events.

  


  I am using :

  


  


  av_write_frame(AVFormatContext, AVPacket) ;

  


  


  and

  


  


  av_interleaved_write_frame(AVFormatContext, AVPacket) ;

  


  


  What is your suggestion/idea ?
Thank you in advance.