Recherche avancée

Sur d’autres sites (8048)

• FFMPEG Seeking with concat demuxer causes video & audio to be out of sync

  20 février 2023, par Garuuk

  I have a very simple use case that's driving me bananas.

  


  My problem and question :

  


  I'm using ffmpeg version 5.1.2 on a MacOS and i'm using ffmpeg seeking and concat demuxer to cut many 1 minute videos into 15 seconds chopped up over 12 clips where every clip is just 2 seconds from the same video (kind of like a mini teasers for the video). I would really like to not have to re-encode to make the video processing as fast as possible.

  


  First, I take each 1 minute video and cut it up into 12 clips (I do all this programmatically in python fwiw)

  


  ffmpeg -ss 0 -i input.mp4 -t 2 -c copy -y cut_1.mp4
ffmpeg -ss 4 -i input.mp4 -t 2 -c copy -y cut_2.mp4
ffmpeg -ss 8 -i input.mp4 -t 2 -c copy -y cut_3.mp4
...
...


  


  I then write all the output file names to my concat_manifest.txt

  


  file cut_1.mp4
file cut_2.mp4
...
...


  


  Then I run my concat command :

  


  ffmpeg -f concat -i concat_manifest.txt -c copy -y concat_video.mp4


  


  This works really fast but the audio and video at the stitch point get out of sync and sometimes the video just chokes & lags. It's mostly not a smooth experience.

  


  What I have tried :

  


  

  1. using the concat protocol with intermediate profiles : ffmpeg.org/wiki/Concatenate#demuxer

  


  2. Putting the -ss when I seek after the -i. This makes everything worse

  


  3. Playing around with different -ss values. This has some noticeable affects but it's not obvious why yet.

  


  4. I've also read from the ffmpeg resource regarding seeking and copying :

  


  


  Which leads me to believe that maybe because ffmpeg is using timestamps instead of frames, seeking isn't accurate using -ss when using the concat demuxer

  


  Is there a way to get concat demuxer cutting and concatenating the video where the audio is somewhat in sync with the video ?

  


  Thanks

  


  EDIT : I found an answer and i'll be posting the solution in the coming few days.

  


• Can you stream video with ffmpeg and opencv without long buffers

  13 septembre 2019, par steve

  I’m successfully getting a video stream using ffmpeg, and displaying with opencv, but the video starts and stops very often and is not as smooth as when played on a browser. Is there a way to get the video stream to be as smooth as on a browser ?

  I’ve tried playing with ffmpeg parameters as well as having multiple pipes to stitch together a single video.

  import cv2
  
  import numpy as np
  
  import subprocess as sp
  
  import time
  
  
  
  
  
  # Playlist manifest for video from Nevada DOT traffic camera
  
  VIDEO_URL = "https://wowza1.nvfast.org/bmw3/charleston_and_fremont_public.stream/playlist.m3u8"
  
  
  
  width = 360
  
  height = 240
  
  
  
  pipe = sp.Popen([ 'ffmpeg', "-i", VIDEO_URL,
  
              "-loglevel", "quiet", # no text output
  
              "-an",   # disable audio
  
              "-f", "image2pipe",
  
              "-pix_fmt", "bgr24",
  
              "-r", "15", # FPS
  
              "-hls_list_size", "3", 
  
              #"-hls_time", "8" 
  
              "-vcodec", "rawvideo", "-"],
  
              stdin = sp.PIPE, stdout = sp.PIPE)
  
  
  
  while True:
  
  
  
          # Convert bytes to image
  
          raw_image = pipe.stdout.read(width*height*3) # read 432*240*3 bytes (= 1 frame)
  
          img =  np.fromstring(raw_image, dtype='uint8').reshape((height,width,3))
  
          raw_image = np.copy(img)
  
  
  
          # Show image
  
          cv2.imshow('pipe', img)
  
          cv2.waitKey(1)
  
          time.sleep(0.05) # This is to slow down the video so it plays more naturally

  The expected output is a opencv window that displays the video just like in https://cctv.nvfast.org/

  I assume the problem lies in ffmpeg not getting the video chunks.

• bash variable changes in loop with ffmpeg

  17 septembre 2018, par Mike

  I wrote a skript to quickly create short preview clips from vides I recorded on timestamps that I found worth checking out later for cutting.
  My file with the timestamps is written like this

  FILE_NAME1#MM:SS MM:SS
  
  FILE_NAME2#MM:SS MM:SS MM:SS MM:SS

  example :

  MAH01728#02:47 03:34 03:44 05:00 06:08 06:55

  The script looks like this :

  #!/bin/bash
  
  while read f
  
   do
  
  
  
   file=$(echo $f | cut -d"#" -f1)
  
   filename=${file}".MP4"
  
   timestamps=$(echo $f | cut -d"#" -f2)
  
  
  
  for time in $timestamps 
  
   do 
  
    ffmpeg -ss 00:${time}.0 -i "orig/${filename}" -c copy -t 10 "preview/${file}_${time}.MP4"
  
   done
  
  done < $1

  The script gets half of the previews that I want and on the other the filename is messed up and ffmpeg complains that the file is not found :

  orig/714.MP4: No such file or directory
  
  orig/00:58 01:25.MP4: No such file or directory

  So I modified the script for trouble shooting and just put an echo in front of the ffmpeg command - now all file names are correct. What am I missing ?

  ffmpeg -ss 00:01:47.0 -i orig/MAH01714.MP4 -c copy -t 10 preview/MAH01714_01:47.MP4
  
  ffmpeg -ss 00:02:00.0 -i orig/MAH01713.MP4 -c copy -t 10 preview/MAH01713_02:00.MP4
  
  ffmpeg -ss 00:00:58.0 -i orig/MAH01712.MP4 -c copy -t 10 preview/MAH01712_00:58.MP4
  
  ffmpeg -ss 00:01:25.0 -i orig/MAH01712.MP4 -c copy -t 10 preview/MAH01712_01:25.MP4