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• FFmpeg image2 output : Control JPG image quality when using mjpeg_qsv

  11 avril 2022, par clic

  My FFmpeg command ouputs a series of JPG images. Simplified :

  


  


  ffmpeg -f dshow -video_size 3840x2160 -framerate 25 -i "video=My
Webcam" -qscale:v 5 -vcodec mjpeg_qsv "C :\out\%d.jpg"

  


  


  I want to use -vcodec mjpeg_qsv to leverage GPU acceleration. Usually (without "_qsv") I can control JPG image quality by using qscale:v , but it seems to have no effect in combination with mjpeg_qsv.

  


  Is it even possible to control JPG image quality when using mjpeg_qsv ? If yes, any ideas how ? Thanks !

  


• VB.NET : How to maintain main form control during loops in other sub ?

  5 février 2015, par Zed Machine

  I have a program with only one form.
  By pressing a button it starts a ffmpeg conversion.

  In the main form, in textboxes, ffmpeg stats are outputted. This is possible by taking StandardError output from ffmpeg.

  Public Sub Console()
  
          Dim Process As New Process 
  
  
  
          Process.StartInfo.UseShellExecute = False
  
          Process.StartInfo.RedirectStandardError = True
  
          Process.StartInfo.RedirectStandardOutput = True 
  
          Process.StartInfo.FileName = current_ffmpeg_path 
  
          Process.StartInfo.Arguments = input_params 
  
          Process.StartInfo.CreateNoWindow = True 
  
          Process.Start() 
  
  
  
          Dim ffmpeg_stats_output As System.IO.StreamReader = Process.StandardError
  
  
  
          Do While Process.HasExited = False
  
          [update all main form textboxes by taking input string from ffmpeg and elaborate it]
  
          Loop
  
  End Sub

  The problem is that while this loop is executed the textboxes and progress bar are updated but the main form cannot be modified. There is in fact no control at all by user. So if I want to make a button to stop/pause ffmpeg in main form this cannot be pressed as anything else on the main form.

  there is a way to maintain loops inside other Sub without loose control of main form while they’re running ?

  I tried to fix it by calling another dialog form with textboxes and progress bar. But even this form loose completely control until the process is finished.

  To send pause/stop conversion to ffmpeg (that runs without a window) is it correct use :

  Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
  
  SendKeys.Send("q")
  
  SendKeys.Send("^s") 
  
  End Sub

  or must be specified that this key is sent to the current running Process ?

• 2-pass rate control in HEVC encoder or x265

  6 mai 2021, par Alearner

  I want to use 2-pass rate control in the HEVC encoder reference code but I do not know if there is a configuration setting to do it. My goal is to encode an original sequence in the 1st-pass rate control and encode a filtered sequence of the original sequence in the 2nd-pass.

  


  I see this can be done in FFmpeg and x265, but giving two different input videos (original and filtered) to the encoder, does it still even make sense ? Any ideas on how to do it in the HEVC encoder/x265 or any comments would be appreciated.