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• Improve ffmpeg scene detection in particular scenario

  17 septembre 2021, par Nobody-Knows-I-am-a-Dog

  I have 50 hours of video where a speaker is in the lower right corner of the video and the by far larger part of the video consists of slides in the center. The speaker moves a bit, the slides transition into the video. I need to detect the time codes of the slide transitions. +- 1 second precision is fine. I am playing around with select filters in ffmpeg such as ffmpeg -i lecture.mp4  -filter:v "select='gt(scene,0.1)',showinfo"   -f null - but I have remaining problems where some help or hint would be highly appreciated.

  


  Problem 1 : Speaker movement occasionally triggers false positives. If there is some possibility to restrict frame comparison to a certain (spatial, cropped) area of the scene then I could focus on the slide area and this would greatly help.

  


  Problem 2 : Speed of slide transition is slow so I occasionally miss a transition since the change from frame(n) to frame(n+1) is too small. It would be great if I could compare, for example, frame(n) to frame(n+10) for threshold detection. ffmpeg scene detection : check only every nth frame ? does not help here, because it only checks every n-th frame but still compares a frame with its immediate neighbor.

  


  Of course, both problems can be solved by producing a cropped version with reduced framerate. However, I am looking for a solution where I can do this in a single pass with some complex filter expression ... and this is exactly the place where my own experience with ffmpeg fails me and where I would appreciate some help.

  


  Problem 3 : Occasionally a single slide transition triggers several times in a row throughout the transition. I have no idea how to solve this in ffmpeg.

  


• Black screen when recording specific screen / window using ffmpeg [closed]

  16 mai, par Mark Brin

  Issue :
I'm trying to capture the specific window using ffmpeg & i've tried these below command for that :

  


  ffmpeg -f gdigrab -framerate 30 -i title="Window Title" -b:v 3M -pix_fmt yuv420p output_FILENAME.webm


  


  And also try changing output format to .mp4

  


  ffmpeg -f gdigrab -framerate 30 -i title="Window Title" -b:v 3M -pix_fmt yuv420p output_FILENAME.mp4


  


  but the output video just shows the black screen with cursor.

  


  What i've tried :

  


  


  • Tried online solutions like Recording Screen with FFmpeg, How to record a specific window using ffmpeg ?, Record specific window using ffmpeg, but none of them worked.

    


  


  • even tried some of the tweaks like removing flags like -pix_fmt yuv420p also tried -f d3d11grab but didn't work.

    


  


  • When i try desktop capture it works completely fine.

    


  


  • I'm using this command to confirm that i'm using correct window title

    


  


  


  Get-Process |
  Where-Object { $_.MainWindowTitle -ne "" } |
  Select-Object -Unique MainWindowTitle


  


  System I'm using :

  


  Windows 11

  


• Getting ffmpeg to capture the full screen of xfvb-run screen running puppeteer script, and send it over rtmp

  30 janvier, par james

  My problem

  


  I can't get ffmpeg or xvfb-run to stream the full screen to ffplay/videolan, it only captures a part of the screen.

  


  Update 2

  


  I answered the question myself in a follow up answer, hopefully it can be useful for someone else with the same problem.

  


  Update 1

  


  So the problem is definitely with xvfb-run, since the two following commands, still give a webm file, that only show parts of the screen

  


  ffmpeg -f x11grab -i :99 -g 50 -b:v 4000k -maxrate 4000k -bufsize 8000k -f webm -s 384x216 "blank.webm"

  


  xvfb-run -n 99 -a --server-args="-screen 0 1024x8000x24 -ac -nolisten tcp -dpi 96 +extension RANDR" "node index.js"

  


  What I've tried

  


  

  • I've tried changing ffmpeg command and xvfb-run, for example adding "-vf format=yuv420p" or "-filter:v "crop=iw-400:ih-40,scale=960:720" to ffmpeg command

  


  • I've tried to show other applications under xvfb-run instead of puppeteer (chrome..)

  


  • Recording screen with ffmpeg and saving it to a file, to see if there's a problem with the rtmp stream

  


  


  But still no luck. That's why I'm reaching out to the stackoverflow community.

  


  xvfb-run command

  


  xvfb-run -n 99 -a --server-args="-screen 0 1024x8000x24 -ac -nolisten tcp -dpi 96 +extension RANDR" "node index.js"

  


  ffmpeg command to capture xvfb-run virtual screen

  


  ffmpeg -f x11grab -i :99 -f pulse -i default -c:v libx264 -c:a aac  -g 50 -b:v 4000k -maxrate 4000k -bufsize 8000k -f flv -listen 1 rtmp://localhost:4444/stream

  


  And finally to show the rtmp stream

  


  ffplay -fflags -nobuffer -flags low_delay -probesize 32 -flags low_delay -analyzeduration 0 -i rtmp://localhost:4444/stream

  


  The puppeteer script (index.js) which xfvb-runs

  


  

import puppeteer from 'puppeteer';
let initPuppeteer = async () => {
  const launchArgs = [
    //'--window-size=1280,1024',
    '--disable-web-security',
    '--disable-features=IsolateOrigins',
    '--disable-site-isolation-trials',
    '--app',
    '--kiosk',
  ]
  await puppeteer.launch({headless: false, ignoreDefaultArgs: ["--enable-automation"], args: launchArgs});
  const page = await this.browser.newPage();
  const device = puppeteer.devices['Nexus 10'];
  await page.emulate(device);
  await page.goto("https://google.com");
}
initPuppeteer()