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• FFMPEG - Overlaying video with transparency, alpha has strange threshold

  6 mars 2019, par tanker_

  I’m attempting to overlay an Apple ProRes 4444 video with a alpha/transparency onto a normal video. However, upon inspecting the final output from FFMPEG, compared to the same files overlaid on top of one another and rendered in Final Cut Pro, there is a discrepancy in how they render the edges around the object.

  Screenshot comparison :

  

  Additional closeup :

  

  Here is my input :

  ffmpeg \
  
      -i background.MOV -x264opts colormatrix=bt709 \
  
      -i alpha_object.MOV -x264opts colormatrix=bt709 \
  
      -filter_complex " \
  
          [0:v]setpts=PTS-STARTPTS, scale=1920x1080[top]; \
  
          [1:v]setpts=PTS-STARTPTS, scale=1920x1080, \
  
               colorchannelmixer=aa=1.0[bottom]; \
  
          [top][bottom]overlay=shortest=1" \
  
      -vcodec libx264 -qp 15 -an -shortest output.MOV

  Any idea what could be wrong ? Is there a option within FFMPEG’s available filters that I’m missing ?

  All files are ingested and rendered in 1920x1080.

• how to set ffmpeg bitrate, frame per second when scalling from low to high resolution/ high to low

  21 janvier 2015, par user2303069

  I’m developing a video sharing app for mobile device users. I noticed if I convert video with ffmpeg from a low(ex 240x320) to a higher resolution(ex 480x-1) the video looses quality and also there is no sound at the end. My question to you is how should I filter(how many fps,bitrate ect) the converted file ? In terms of parameters, how should I convert to make sure the video comes out in good quality at it’s destination(the user who will play it on their mobile device[Android/BlackBerry]).

  Here is my current code(java) :

  /************************  CONVERTING    TIME   *************************
  
                         method to convert video-clip
  
  */
  
  if(sn.toString().trim().startsWith("<>")){
  
      String info=sn.toString().trim().substring(2);
  
      String scale=info.substring(0, info.indexOf("."));
  
      String width=scale.substring(0, scale.indexOf("x"));
  
      String name=info.substring(info.indexOf(".")+1, info.length());
  
      String to = null;
  
      String from;
  
  
  
      try{
  
          //calculate to and from
  
          to=name.substring(0, name.indexOf("$"));
  
          from=name.substring(name.indexOf("$")+1, name.lastIndexOf("$"));
  
          gui.textArea1.append("\nStart converting...: to="+to+" from="+from+" fileName="+name);
  
      }catch(NullPointerException npe){
  
          gui.textArea1.append("\nNullpointer in calculate name in converting: "+npe.getMessage());
  
      }
  
  
  
      final Path videoIn = Paths.get("c:\\wamp\\www\\iclips\\videoMessages\\"+name);
  
      final Path encodingFile = Paths.get("c:\\wamp\\www\\iclips\\videoMessages\\scaled-"+name);
  
      final Path errorFile = Paths.get("c:\\ffmpeg\\bin\\error.txt");
  
      String pro;
  
      int w=Integer.parseInt(width);
  
  
  
      if(w<=240){
  
          pro="baseline";
  
      }else if(w>240&&w<=480){
  
          pro="main";
  
      }else if(w>480){
  
          pro="high";
  
      }else{
  
          pro="baseline";
  
      }
  
      //int retCode;
  
  
  
      try {
  
          Files.deleteIfExists(encodingFile);
  
          Files.deleteIfExists(errorFile);
  
  
  
          final ProcessBuilder pb 
  
              = new ProcessBuilder("c:\\ffmpeg\\bin\\ffmpeg.exe",
  
                  "-i", videoIn.toString(),
  
                  "-y", 
  
                  "-vf", "scale="+width+":-1", 
  
                  // "-pix_fmt","yuv420p",   
  
                  "-vcodec", "libx264",
  
                  "-vprofile", pro,    
  
                  "c:\\wamp\\www\\iclips\\videoMessages\\scaled-"+name
  
          ); //or other command....                    
  
  
  
          pb.redirectError(errorFile.toFile());
  
          pb.redirectOutput(encodingFile.toFile());
  
  
  
          final Process p = pb.start();
  
          try {
  
              p.waitFor();
  
              if(p.exitValue()==0){
  
                  gui.textArea1.append("\n+++++++++++++Vic-^clip converted successfully:"
  
                          + " ExitValue=["+String.valueOf(p.exitValue())+"] ++++++++++++++");
  
                  if(Files.deleteIfExists(videoIn)){
  
                      gui.textArea1.append("\n"+videoIn.toString()+" deleted!");
  
                  }
  
                  sendMsg("Scalling successfull:-)   Video-clip name=scaled-"+name+"_", "\nSent scaled successfull "+username);
  
                  NotifyClientOfScaledVideoMessage(to,"^scaled-"+name+"_");
  
              }else{
  
                  gui.textArea1.append("\nSomething went wrong with process-convert: ExitValue="+String.valueOf(p.exitValue()));
  
                  sendMsg("Unable to scale video, try again._", "\nSent scaled failed to "+username);
  
              }
  
          } catch (InterruptedException e) {
  
              gui.textArea1.append("\nInterrupted process convert: "+e.getMessage());
  
          }
  
      } catch (IOException e) {
  
          // deal with e here
  
          gui.textArea1.append("\nIOException in Convert Video: "+e.getMessage());
  
      }
  
  }

  Thank you very much.

• Crop video into a 4x4 grid/tiles/matrix efficiently via command-line ffmpeg ?

  22 avril 2017, par Dylan

  Hello Stackoverflow community !

  I dread having to ask questions, but there seems to be no efficient way to take a single input video and apply a matrix transformation/split the video into equal sized pieces, preferably 4x4=16 segments per input.

  I tried using all the libraries such as ffmpeg and mencoder, but having 16 outputs can be as slow as 0.15x. The goal of my project is the split the video into 16 segments, rearrange those segments and combine back into a final video ; later reversing the process in HTML5 canvas. Here is a picture to help you understand what I am talking about :
  the source but also the final destination after reorganizing the pieces

  after the segments are exported, I will recombine the pieces in a puzzle manner (they are also inverted and rotated but unrelated)

  I do not believe you can do this all in one command, so my goal is to crop into 16 mapped outputs quickly, then reassemble them in a different order. But I can do the other parts myself. Ideally there would be a way to move pixel blocks eg 100x100 and just move them around. My math is not strong enough..
  I really appreciate the work you guys do !

  admin@dr.com