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• Not getting accurate time stamp from FFMPEG after converting datetime to Unix

  13 janvier 2023, par Jacob

  I am creating a video editing application. I have created an ObservableCollection which contains information regarding every frame, 30 per second. I have computed the DateTime per frame as VideoCreationDate + FrameNumber / 29.97. When I display the current time and date with a TextBlock overlaying each frame, the time is perfectly accurate. However, once I convert the date time to Unix time and use it as parameters in the FFMPEG DrawText filter, the time is slightly off. The first few frames are accurate and progressively get worse off the more I scrub through the frames. I am checking the Unix timestamp on each frame and it is correct but for some reason, when I render the FFMPEG command, it converts the timestamp to date time inaccurately.

  


  Below is the method to convert DateTime to Unix :

  


  public long ToUnixTimestamp(DateTime value)
    {
        var dateTimeOffset = new DateTimeOffset(value);
        var unixDateTime = dateTimeOffset.ToUnixTimeSeconds();
        Debug.WriteLine(unixDateTime);
        return unixDateTime;
    }


  


  Below is part of the FFMPEG string containing the DrawText filter :

  


  drawtext=text=\'%{pts\:localtime\:" + ToUnixTimestamp(CurrentFrame.FrameTime) + @"\:'%#I\:%M%p'}\'


  


  I am not sure if I am doing something wrong or if this is a flaw with FFMPEG. Any ideas ?

  


• Using ffmpeg, extract small part of .m4a audio file specifying exact start and end time

  31 août 2015, par Kes

  I have Linux mint 17.1.

  When I use ffmpeg to cut out a section of a 4 hour long .m4a audio file as follows :

  ffmpeg -ss 0:10:00 -i in_file.m4a -vn -c copy -t 0:40:00 out_file.m4a

  the correct position and duration of extract is extracted and the file plays just fine.

  How can I extract using the end time of the extract, not the duration ?
  ie in this case the start time and end time are 0:10:00 and 0:00:50.

  Thank you

• python - record and preview webcam at the same time, using e.g. ffmpeg

  18 décembre 2024, par Jan Oechsler

  I want to record webcam with sound using python. After tryng multiple different methods, ffmpeg with the python wrapper showed the best results.

  


  Recording works, but how can I preview the webcam at the same time, so I know where I am pointing the cam at ?

  


  I've seen this post, but I dont understand how I could implement this in python, using the wrapper.

  


  Any ideas on how to do this ? Or if there is another, easier, solution to record webcam video with sound and preview it simultaneously from within a python (Qt) application ?

  


  This is my code so far :

  


  import ffmpeg
import time

process = (
    ffmpeg
    .input('video=Integrated Camera:audio=Microphone Array (Realtek(R) Audio)', format='dshow')
    .output('out.mp4', pix_fmt='yuv420p')
    .overwrite_output()
    .run_async(pipe_stdin=True, pipe_stderr=True, quiet=True)
)

# This is just to simulate some time-
time.sleep(10)

process.stdin.write('q'.encode())
process.communicate()
process.wait()

print('done')