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• Fast seeking ffmpeg multiple times for screenshots

  14 septembre 2021, par user3786834

  I have come across https://askubuntu.com/questions/377579/ffmpeg-output-screenshot-gallery/377630#377630, it's perfect. That has done exactly what I wanted.

  



  However, I'm using remote URLs to generate the screenshot timeline. I do know it's possible to fast seek with remote files using https://trac.ffmpeg.org/wiki/Seeking%20with%20FFmpeg (using -ss before the -i) but this only runs the once.

  



  I'm looking for a way to use the

  



  ./ffmpeg -i input -vf "select=gt(scene\,0.4),scale=160:-1,tile,scale=600:-1" \
-frames:v 1 -qscale:v 3 preview.jpg


  



  command but using the fast seek method as it's currently very slow when used with a remote file. I use PHP but I am aware that a C method exists by using av_seek_frame, I barely know C so I'm unable to implement this into a PHP script I'm writing. So hopefully, it is possible to do this directly with ffmpeg in the PHP system() function.

  



  Currently, I run seperate ffmpeg commands (with the -ss method) and then combine the screenshots together in PHP. However, with this method it will be refetching the metadata each time and a more optimized method would be to have it all happen in the same command line because I want to reduce the amount of requests made to the remote url so I can run more scripts in sequence with each other.

  



  Thank you for your help.

  


• FFmpeg - Multiple videos with 4 areas and different play times

  25 mai 2018, par Robert Smith

  I have videos as follows

  video   time
  
  ======= =========
  
  Area 1:
  
  video1a    0-2000
  
  video1b 2500-3000
  
  video1c 3000-4000
  
  
  
  Area 2:
  
  video2a  300- 400
  
  video2b  800- 900
  
  
  
  Area 3:
  
  video3a  400- 500
  
  video3b  700- 855
  
  
  
  Area 4:
  
  video4a  400- 500
  
  video4b  800- 900

  Basically these are security camera outputs and should display in 4 areas :

  So far I have the following :

  ffmpeg
  
      -i 1.avi -i 2.avi -i 3.avi -i 4.avi
  
      -filter_complex "
  
          nullsrc=size=640x480 [base];
  
          [0:v] setpts=PTS-STARTPTS, scale=320x240 [upperleft];
  
          [1:v] setpts=PTS-STARTPTS, scale=320x240 [upperright];
  
          [2:v] setpts=PTS-STARTPTS, scale=320x240 [lowerleft];
  
          [3:v] setpts=PTS-STARTPTS, scale=320x240 [lowerright];
  
          [base][upperleft] overlay=shortest=1 [tmp1];
  
          [tmp1][upperright] overlay=shortest=1:x=320 [tmp2];
  
          [tmp2][lowerleft] overlay=shortest=1:y=240 [tmp3];
  
          [tmp3][lowerright] overlay=shortest=1:x=320:y=240
  
      "
  
      -c:v libx264 output.mp4

  But there are two things I am missing :

  • The above is only for 4 video files, I need a way to add additional files to each area (for example video1b should play at its corresponding time after video1a in the same area)
  • How do I specify the beginning/ending time as shown above for each file ?

• FFMPEG stereo track stops capturing at random times during a capture session

  26 mai 2022, par mrwassen

  I am currently working on building a workflow to capture and archive a large stash of family and friends PAL and NTSC VHS tapes. The hardware setup is as follows :

  


  

  • JVC HR-7860S VCR

  


  • s-video / RCA audio >

  


  • ADVC-3000 converter

  


  • SDI / BNC cable >

  


  • Blackmagic Decklink Mini Recorder 4K PCIe card

  


  • installed in a fairly hi-spec windows machine : AMD Ryzen 9 5900X 3.7 Ghz base 12 core, GEFORCE RTX 3060 12 gB, 32 gB ram

  


  


  The plan is to capture to lossless AVI, then drop into an NLE (Vegas Pro v.16) to do a minimal amount of cleanup / trimming, then render to a more compressed video format (TBD) for upload to AWS S3 accessible through a family website.

  


  The issue I am having is that when I run the capture using ffmpeg/directshow e.g. for a perfectly fine 90 min. PAL tape, at some random point of time during the capture one of the 2 stereo channels just stops capturing. This has happened with all of the tapes I have tested so far, and it happens at different times during the same video. I have examined the frames surrounding points in time when this happens, and it doesn't correlate to any transitions or jitter, but often just randomly in the middle of a perfectly smooth scene. Once the one channel stops capturing it never starts back up again during that capture session.

  


  The ADVC-3000 and the VCR are both showing both stereo channels playing normally throughout the capture. The windows machine running the capture hardly breaks a sweat at any time, and the transfer easily keeps up constantly showing a speed = 1x which I assume means nothing lagging. Also there are no video/audio sync issues at any point in time even towards the end of long tapes e.g. 90 mins.

  


  I am fairly new at ffmpeg, so I have spent extensive amounts of time reading up on forum posts and experimenting and have ended up with the following syntax :

  


  ffmpeg -y -f dshow -rtbufsize 2000M -i video="Blackmagic WDM Capture":audio="Blackmagic WDM Capture" -codec:v v210 -pix_fmt yuv422p -codec:a pcm_s16le -b:a 128k -t 02:00:00 -r 25 -threads 4 -maxrate 2500k -filter:a "volume=1.5" output_v210_audio.avi


  


  The capture runs without a single dropped frame, the only error I am getting when launching (and perhaps this is a smoking gun ?) is :

  


  


  "Non-monotonous DTS in output stream 0:1 ; previous : 0, current : -30 ;
changing to 1. This may result in incorrect timestamps in the output
file."

  


  


  I have tried to troubleshoot this in the hopes that it is tied to my issue but so far without luck.

  


  Hoping somebody can help correct or modify my command line or perhaps other ideas to help resolve the issue.