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• Data lost in ffmpeg in overlay / steganography using ffmpeg

  3 août 2020, par g Kishore

  Goal : Embedding some textual information into a video(steganography) using LSB encoding. And retrieving the embedded text.

  


  Procedure followed :

  


  

  1. Extracted one frame from video :
ffmpeg -i -vf "select=eq(n,34)" -vframes 1 out.bmp

  


  2. LSB encoding of text into out.bmp using C-code :
NOTE : Decoding of embedded text from out.bmp is working fine[c-code]

  


  3. Insert out.bmp back into original video :
ffmpeg -i -i out.bmp -filter_complex "[0:v][1:v]overlay=enable='between(n,0,0)'[out]" -acodec copy -map
"[out]" -map 0:1 output.mp4

  


  4. Extracted frames from encoded video "output.mp4" :
ffmpeg -i output.mp4 frames%d.bmp
NOTE : Replaced image is present in extracted frames

  


  5. Decoding the text from frames0.bmp, frames1.bmp, frames2.bmp using C-Code
NOTE : not able to decode the text. I tried comparing image data of out.bmp & frames0.bmp, frames1.bmp, frames2.bmp. Lots of changes are there.

  


  


  PS :
. C-code used to encode & decode text into the image is working well. No ambiguity in it.
. Encoded video is playable properly. Only issue is loss of embedded text while overlaying the encoded image back into the video

  


  Any help is appreciated.

  


• Recording live stream with intermittent no audio with FFmpeg

  15 décembre 2022, par charlie-bird

  I'm trying to record a live stream with ffmpeg and having an issue with the audio.
The stream has video and audio, until it goes to video only for a few minutes and back to audio+video.
  
A : XXXXXX________YYYYYY_______ZZZZZZ
  
V : XXXXXXOOOOO0YYYYYYOOOOOZZZZZZ
  

  


  When I stop the recording and look at the output file, the absence of audio is messing stuff up. Instead of having no audio during the "breaks" ffmpeg wrote the audio track from after the break over the video, completely disconnecting audio and video
  
A : XXXXXXYYYYYYYZZZZZZZZZ
  
V : XXXXXXOOOOOOOOYYYYYYOOOOOOOZZZZZZ
  

  


  Is there an argument or parameter to force the recording of an "empty" audio track over the video when there's no audio, to keep both in sync ?

  


  Right now, not using any options

  


  ffmpeg -i "https://input.m3u8" ~/Outputfile.mp4


  


  Tried with map as below, same issue

  


  ffmpeg -i "https://input.m3u8" -map 0:a -map 0:v ~/Outputfile.mp4


  


  EDIT :
Also tried with a simple copy, in that case the audio stops but then isn't recorded when it comes back

  


  ffmpeg -i "https://input.m3u8" -map 0:a -map 0:v -c copy ~/Outputfile.ts


  


  EDIT 2 :
I've found a workaround. I re-stream the live stream using VLC on a local port and record copy with ffmpeg, and now it's all in sync

  


  ffmpeg -i "http://10.10.10.10:1234" -c copy ~/Outputfile.ts


  


  I would still like to be able to do this directly, but in the meantime that works.

  


• How do i compress a video file in c# (Xamarin android)

  1er août 2016, par stackOverNo

  I’m currently working on a xamarin.android project, and am attempting to upload a video to an aws server, and then also be able to play it back. The upload is working correctly as far as I can tell.

  I’m retrieving the file from the user’s phone, turning it into a byte array, and uploading that. This is the code to upload :

  if (isImageAttached || isVideoAttached)
  
              {
  
                  //upload the file 
  
                  byte[] fileInfo = System.IO.File.ReadAllBytes(filePath);
  
                  Task<media> task = client.SaveMediaAsync(fileInfo, nameOfFile);
  
                  mediaObj = await task;
  
  
  
                  //other code below is irrelevant to example
  
              }
  
  </media>

  and SaveMediaAsync is a function I wrote in a PCL :

  public async Task<media> SaveMediaAsync(byte[] fileInfo, string fName)
  
      {        
  
          Media a = new Media();
  
          var uri = new Uri(RestUrl);
  
  
  
          try
  
          {
  
  
  
              MultipartFormDataContent form = new MultipartFormDataContent();
  
              form.Add(new StreamContent(new MemoryStream(fileInfo)), "file", fName);  //add file
  
  
  
              var response = await client.PostAsync(uri, form);            //post the form   client is an httpclient object
  
              string info = await response.Content.ReadAsStringAsync();
  
  
  
      //save info to media object
  
              string[] parts = info.Split('\"');
  
              a.Name = parts[3];
  
              a.Path = parts[7];
  
              a.Size = Int32.Parse(parts[10]);
  
  
  
          }
  
          catch(Exception ex)
  
          {
  
      //handle exception
  
          }
  
  
  
          return a;
  
  
  
      }
  
  </media>

  After uploading the video like that, I’m able to view it in a browser using the public url. The quality is the same, and there is no issue with lag or load time. However when I try to play back the video using the same public url on my app on an android device, it takes an unbelievably long time to load the video. Even once it is loaded, it plays less than a second of it, and then seems to start loading the video again(the part of the progress bar that shows how much of the video has loaded jumps back to the current position and starts loading again).

   VideoView myVideo = FindViewById<videoview>(Resource.Id.TestVideo);
  
  
  
   myVideo.SetVideoURI(Android.Net.Uri.Parse(url));
  
  
  
   //add media controller
  
   MediaController cont = new MediaController(this);
  
   cont.SetAnchorView(myVideo);
  
   myVideo.SetMediaController(cont);
  
  
  
   //start video
  
   myVideo.Start();
  
  </videoview>

  Now I’m trying to play a 15 second video that is 5.9mb. When I try to play a 5 second video that’s 375kb it plays with no issue. This leads me to believe I need to make the video file smaller before playing it back, but I’m not sure how to do that. I’m trying to allow the user to upload their own videos, so I’ll have all different file formats and sizes.

  I’ve seen some people suggesting ffmpeg for a c# library to alter video files, but I’m not quite sure what it is I need to do to the video file. Can anyone fill in the gaps in my knowledge here ?

  Thanks for your time, it’s greatly appreciated !