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• How to reduce bitrate with out change video quality in FFMPEG

  13 juillet 2016, par Muthu GM

  I’m using FFMPEG C library. I’m use modified muxing.c example to encode video. Video quality is reduce frame by frame when I control bitrate (like 1080 x 720 - bitrate 680k ). But same image I using FFMPEG command line tool to encode same bitrate 680k image quality to not change.

  What is the reason for same image and bitrate encoded video quality reduce whan I encode using C API and reason why quality did not change command line tool.

  I use :

  Command line arg :

  • ffmpeg -framerate 5 image%d.jpg -c:v libx264 -b:v 64k -pix_fmt yuv420p
    out.mp4

  Muxing.c(modified) Codec setting :

  • fps = 5 ;
  • CODEC_ID = H264 (libx264) ;
  • Pixel_fmt = yuv420 ;
  • Image decoder = MJPEG ;
  • bitrate = 64000 ;

  The video size are same but quality is reduce frame by frame in muxing.c
  but same bitrate video quality is perfect.

  please provide how to I reduce bitrate with out change quality using FFMPEG C API.

• How can i use ffmpeg.exe command line to create a video file from number of images on hard disk ?

  22 juillet 2016, par TheLost Lostit

  In command prompt window i typed in the directory of the images :

  D :\SavedScreenshots>ffmpeg.exe -r 3 -i Imgp%04d.bmp -s 720x480 test.avi

  The images file are Bmp type.
  The first image file name is : screenshot0.bmp
  The last one is : screenshot168.bmp

  Example of one image details : Width 1920 Height 1080 Bit Depth 32

  The ffmpeg.exe file is in the same directory of the images.

  In the prompt windows console ouput i see :

  [image2 @ 00000000025624a0] Could find no file with path ’Imgp%04d.bmp’ and index in the range 0-4
  Imgp%04d.bmp : No such file or directory

  Then how should i do it the command line ?

  I found the problem and now it’s working but it’s very strange.

  In c# i create the screenshots of my desktop this images on the hard disk i want to create video file from.
  In c# i did in a timer tick event :

  int count = 0;
  
          private void timer1_Tick(object sender, EventArgs e)
  
          {
  
              Bitmap bmp = new Bitmap(sc.CaptureScreen());
  
              bmp.Save(@"D:\SavedScreenshots\screenshot" + count + ".bmp");
  
              bmp.Dispose();
  
              count ++;
  
          }

  This saved the images on the hard disk all of them in sizes between 129-132kb each file. I could edit/open the images and see them no problems but ffmpeg could not handle them gave me this error.

  Now i changed the code in the c# to this :

  bmp.Save(@"D:\SavedScreenshots\screenshot" + count + ".bmp", System.Drawing.Imaging.ImageFormat.Bmp);

  I added the part : System.Drawing.Imaging.ImageFormat.Bmp

  Now each image file it’s size is about 7MB !!!!
  And now ffmpeg can handle it with the command line :

  ffmpeg.exe -framerate 3 -i screenshot%d.bmp -vf scale=ntsc,setdar=16/9 test.avi

  I wonder why when the images size was 130KB ffmpeg couldn not handle it didn’t find the files or directory and when they are 7MB it does find and create the video file ?

  Even now when i type as command line :

  ffmpeg  -i screenshot%03.bmp -s 720x480 test.avi

  I’m getting erorr not such file or directory

  Only when i type :

  ffmpeg  -i screenshot%d.bmp -s 720x480 test.avi

  It’s working.

  Why when doing screenshot%3.bmp it’s not working but screenshot%d.bmp does working ?

  Also doing screenshot0.bmp worked. Only screenshot%3.bmp not working.
  And in all examples i saw i had to make screenshot%3 or %2 but they give me the error no such directory file.

• What should be the timing to capture screenshots as images and then convert the images to video file using ffmpeg ?

  22 juillet 2016, par TheLost Lostit

  I have a timer tick event where i take screenshots every 10ms

          int count = 0;
  
          private void timer1_Tick(object sender, EventArgs e)
  
          {
  
              Bitmap bmp = new Bitmap(sc.CaptureScreen());
  
              bmp.Save(@"D:\SavedScreenshots\screenshot" + count + ".bmp", System.Drawing.Imaging.ImageFormat.Bmp);
  
              bmp.Dispose();
  
              count ++;
  
          }

  Then i i’m using ffmpeg command line in command prompt window to create a video file from all the images :

  ffmpeg -framerate 2 -i screenshot%d.bmp -c:v libx264 -r 30  -pix_fmt yuv420p out.mp4

  Every bitmap file on hard disk it’s size is 7.91 MB
  The details : 1920x 1080 and Bit depth 32

  The problem is when making the ffmpeg command line with -framerate 2 then when i play the video file in windows media player it’s very very slow.
  When i saet the framerate to 10 then it’s too fast.
  When i set the framerate to 4 i’m getting error in yellow say too large.

  But maybe the problem is that i’m taking a screenshot every 10ms ? Maybe i should take a screenshot every 1000ms ? And then what should i change in the ffmpeg command line ?

  I want it to be like a regular video file speed. Not too fast and not too slow.
  What i’m capturing in the screenshot is my desktop screen and later i want to upload and show it to some support help in a forum.