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• Record live stream using ffmpeg as Process in Java

  26 décembre 2020, par Serbroda

  I can not figure out how to start a Process in Java for recording a live stream with ffmpeg.

  



  I've tried several solutions, but my current code looks like this (simplified) :

  



  public void startDownload() {
    String[] processArgs = new String[] {
            "ffmpeg", 
            "-i", 
            "https://bitdash-a.akamaihd.net/content/sintel/hls/playlist.m3u8", 
            "-c", 
            "copy", 
            "-bsf:a", 
            "aac_adtstoasc", 
            "C:\\temp\\test.mp4"
    };
    ProcessBuilder processBuilder = new ProcessBuilder(processArgs);
    try {
        process = processBuilder.start();
        process.wairFor(); // Do I need this? Actually the stream is running forever until I stop it manually.
        BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line = null;
        while ((line = br.readLine()) != null) { // this blocks forever
            System.out.println(line);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}


  



  The problem is, that something blocks the process from starting. In this example the br.readLine() blocks it forever and I can not get any output from the process.

  



  But after killing the jar / stopping launch config in Intellij, the process begins to work and I have to kill it via task manager.

  



  Running a process that is not recording a live stream like just executing ffmpeg works by the way.

  



  I'm using Windows, JDK 14, IntelliJ.

  


• ffmpeg, how to extract single frame, 0.5 seconds before the end ? [duplicate]

  24 avril 2020, par Tonny

  I've got a bunch (several 100) of videos (all different frame-rates and different lengths).
  
Each has an end-title during the last second of the video, that shows some important information I need to check.
  
Playing each video in a player, scrolling to the end and trying to pause it in the last second is just to cumbersome/time-consuming.
  
Grabbing a frame at that position and saving it as an image for each video lets me quickly check the info using the image-preview in my file-manager. Which is much more efficient.

  



  ffmpeg can capture single frames and write them to a jpg or png, but I am at a loss how to extract a frame in the middle of that title sequence. 0.5 seconds before the end of each video would be the sweet spot. (There is a animation effect during that 1 second sequence that makes the text in the video sometimes hard to read, but exactly in the middle the visibility is best.)
  
As far as I can tell ffmpeg can't use offsets "from the end", so I assume ffprobe is probably needed to analyze the video and on basis off that the correct ffmpeg command can be generated.

  



  I can handle the scripting around it to batch-process all the files.
  
Problem is that I'm very unfamiliar with video in general, ffmpeg and ffprobe in particular. I need some help to get started.
  
If someone can explain to me how to get from the full video 'clip.mp4' to the single frame 0.5 seconds before the end in 'clip_frame.jpg' I would be most grateful.

  


• ffmpeg subtitle font size too big

  21 avril 2020, par Harry Vũ

  After making subtitles in Aegisub, I save it as .ass file, with font size set from style manager,
I used this command

  



  ffmpeg -i video.mp4 -b:v 1M -vf subtitles=subtitle.ass out.mp4


  



  but the output file has the font a few sizes too big, larger than the original size I set in Aegisub.
Did I do something wrong ?
This was the intended size :

  



  

  



  And this is the output size :

  



  

  



  Here's the ass file
ass file