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• Calculating PCR (Program clock reference) in MPEG2 Transport stream

  1er octobre 2024, par Tomislav Timic

  i am implementing transcoder and packager for abr protocols (HLS/DASH), and also udp mutlicast as output option. I am currently finishing multiplexing of mpeg 2 transport streams, but i do not really understand how should pcr work, how should I calculate it, I have pts/dts values, is there some formula to derive pcr from pts and/or dts ? When i do tsdump from tsduck with ffmpeg output they have around +100ms PCR delay on PTS.

  


  I found some calculations like this :

  


  (int64_t) ((8.0 * (packetsWritten * TS_PACKET_LENGTH + offset) / tsMuxrate) * TS_CLOCK + 0.5) + pcrStart


  


  But it does not match ffmpeg calculation. When i do like this :

  


  base = (int64_t) packet->dts - (int64_t) (SYSTEM_CLOCK_FREQ_90kHz * 0.1);


  


  It has +100ms delay from PTS. But it is hardcoded.

  


• JavaFX : ffmpeg process finishes writing the file only after closing the program

  16 juin 2024, par The Engineer

  My JavaFX application uses ffmpeg to extract the first frame from a video file. The ffmpeg command is run in a separate thread, and the process ends with a wait. However, despite the fact that the image is saved to a temporary directory (temp/video_preview.jpg ), it becomes available only after the forced termination of the entire program, and not immediately after the completion of the ffmpeg process. I need the image to be available for display in ImageView immediately after the ffmpeg process is completed.
  
https://github.com/Memory420/GifConverter/tree/master

  


  I expected the ffmpeg process to quickly create a picture and I would apply it where I need it.

  


  @FXML&#xA;    private void onDragOver(DragEvent event) {&#xA;        if (event.getDragboard().hasFiles()) {&#xA;            event.acceptTransferModes(TransferMode.ANY);&#xA;        }&#xA;    }&#xA;&#xA;    @FXML&#xA;    private void onDragDropped(DragEvent event) {&#xA;        Dragboard db = event.getDragboard();&#xA;        boolean success = false;&#xA;        if (db.hasFiles()) {&#xA;            List<file> files = db.getFiles();&#xA;            File videoFile = files.get(0);&#xA;            Image image = extractFirstFrameFromVideo(videoFile.getAbsolutePath());&#xA;            mainImage.setImage(image);&#xA;            success = true;&#xA;        }&#xA;        event.setDropCompleted(success);&#xA;        event.consume();&#xA;    }&#xA;</file>

  


  private Image extractFirstFrameFromVideo(String pathToVideo) {
        try {
            ProcessBuilder processBuilder = new ProcessBuilder(
                    ffmpegPath,
                    "-y",
                    "-ss", "00:00:00",
                    "-i", pathToVideo,
                    "-frames:v", "1",
                    outputFilePath  // "temp/video_preview.jpg"
            );

            Process process = processBuilder.start();

            int exitCode = process.exitValue();
            if (exitCode != 0) {
                throw new IOException("ffmpeg process exited with error code: " + exitCode);
            }

            return new Image(new File(outputFilePath).toURI().toString());

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }


  


• How to rename the .wav file which is going to download using the below program ?

  29 avril 2020, par Y V Sravan Kumar Reddy

  from __future__ import unicode_literals
import youtube_dl

ydl_opts = {
    'format': 'bestaudio/best',
    'postprocessors': [{
        'key': 'FFmpegExtractAudio',
        'preferredcodec': 'wav',
        'preferredquality': '192'
    }],
    'postprocessor_args': [
        '-ar', '16000'
    ],
    'prefer_ffmpeg': True,
    'keepvideo': True
}

with youtube_dl.YoutubeDL(ydl_opts) as ydl:
    ydl.download(['https://www.youtube.com/watch?v=JpjEwIceVIo'])


  



  ---

  



  Output :

  



  [youtube] JpjEwIceVIo: Downloading webpage
[download] Speech on Importance of Education in English for Higher Secondary students by Smile Please World-JpjEwIceVIo.webm has already been downloaded
[download] 100% of 1.69MiB
[ffmpeg] Destination: Speech on Importance of Education in English for Higher Secondary students by Smile Please World-JpjEwIceVIo.wav


  



  ---

  



  I want to change the filename to audio1.wav instead of Speech on Importance of Education in English for Higher Secondary students by Smile Please World-JpjEwIceVIo.wav. Please help me with this problem.