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• ffmpeg : How to limit bit rate of video output ?

  27 mars 2017, par Mat

  To a 2GB raw video file taken in front of a greenscreen I want to add the alpha channel.

  My problem is : the output files appear much too large to me (about 20-fold the size of the input), and OpenShot, the video editor, seems unable to handle such huge files. Comparing file properties of input and output shows bitrates of about 15k in the infiles, and 150k-250k in the result files, which seems to pinpoint the problem.

  (By the way, I also want to discard the first part of the clip as well as its audio channel and reduce the frame rate from 30 to 24 fps in the process, which all works fine.)

  This is my command :

  ffmpeg.exe -i  -vf chromakey=0x007d06:0.15:0.0 -ss 40.420 -r 24 -b:v 15840k -maxrate 15840k -bufsize 15840k -an -c:v <encoder> 
  
  </encoder>

  The parameters as I understand them :

  -i  ... infile
  
  -vf chromakey=0x007d06:0.15:0.0 ... chroma, tolerance & blend of greenscreens
  
  -ss 40.420 ... skip before second 40.420 (this works)
  
  -r 24 ... frame rate (this works, too)
  
  -b:v 15804k ... bitrate (seemingly no effect)
  
  -maxrate 15840k ... maximum BitRate (seemingly no effect)
  
  -bufzise 15840k ... Buffer size (can't tell)
  
  -an ... no audio channel (works fine)
  
  -c:v <encoder> ... Video Encoder (ffvhuff, png, qtrle and tiff were tried, all to the same result)
  
   ... outfile
  
  </encoder>

  b, maxrate and bufsize are described as global options. No matter what setting, during the process bitrates of up to some 3000000kbits/s (tiff) are reported.

  (I also added -pixel_format argb, but this, too, seemed to be ignored, ffmpeg always reports to write yuva420p.)

  What am I missing ?

• Livestream screen capture to frontend website with low latency [closed]

  3 juin 2021, par Eddie Huang

  for a project I want to livestream my desktop on my Ubuntu server onto the frontend website (running on the same server using Node/Express).

  


  It would be the same effect as livestreaming with OBS/ffmpeg to Youtube/Twitch and embedding into my own website.&#xA;It has to be low latency (<1 second)

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  Could anyone point me in what protocols/applications/tutorials to use as an outline ?

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• FFMPEG is not recording the whole window

  25 mai 2021, par John

  I'm using FFMPEG to record a window as illustrated in the figure below. In all cases, the right hand side of the recorded window is cropped. The command I'm giving is

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  ffmpeg -f gdigrab -i title="example.txt - Notepad++" output.mkv


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  Any suggestion on how to fix this problem is much appreciated.

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  Here are some additional info :

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  • Running Windows 10

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  • Using ffmpeg-20181215-011c911-win64-static, but I have the same issue using other versions of FFMPEG

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  • Desktop resolution is 3200x1800 (dpi scaling issue ?)

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  This is what the recorded area looks like in the example above

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  Update 1 :

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  Recording the whole desktop works fine, however, when recording a region using x and y offsets, the region captured is correct, but the region indicated is wrong. I illustrate this in the image below that shows a screen capture of the desktop during recording. The background image is a grid and the taskbar has been hidden.

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  The size of the area to capture is specified to 1280x720, but the region indicated is 1600x900. Also, the x offset is specified to 400px, but the region indicted starts at 500px.

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  The area recorded is correct ! The image below shows a screenshot of the recording during playback in vlc, note that the "misplaced" region indicator can be seen

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  Update 2 :

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  I noticed that the cursor, the mouse, is not correctly placed when capturing from the desktop, see recording below. Everything looks fine during recording, but at playback the cursor is misplaced.

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  The command issued for the recording above was :

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  ffmpeg -f gdigrab -framerate 30 -offset_x 1820 -offset_y 100 -video_size 1280x720 -i desktop output5.mkv


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  Windows 10 / ffmpeg-20181215-011c911-win64-static

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