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• How can I concatenate MP4 videos and exactly match this combined video to an audio track in ffmpeg ?

  17 juin 2020, par mattador

  Basically I want to combine 4 videos into a single video, then swap out the concatenated audio for another track. The audio track needs to be unaltered and sync exactly to the video.

  



  Specifically, I'm creating multipaged dynamic audio spectrograms (visualizations of a sound file) using ggplot2 and gganimate in R, which I want to combine using ffmpeg. So the original WAV is chopped up into 3 sec segments, a video is created to visualize frequency changes over time for each segment, which I want to combine into 1 video with the original audio track matched up.

  



  All of my relevant files are at github here in the vids folder : DL link here

  



  The individual dynamic spectrograms export fine (1-4.mp4 in the archive). They are each 20ms too long ; they should be exactly 3s, but otherwise great.

  



  I then use ffmpeg to concatenate them :

  



  ffmpeg -f concat -safe 0 -i "mp4Segments.txt" -codec copy -t 12 -y "(1-4)vid.mp4"


  



  but you can see the end of (1-4)vid.mp4 is getting a little off (the cursor is not all the way to the end, so I guess the video is getting cut off before the end. Not a deal-breaker, since the audio still aligns very well to the video cursor.

  



  Now, since the concatenated video introduces glitchy audio between clips, I want to take the uncut original audio and add that to the assembled video.

  



  ffmpeg -ss 0 -i "(1-4)vid.mp4" -i "origWAV.wav"  -c:v libx264 -map 0:v:0 -map 1:a:0 -c:a aac -ac 1 -b:a 192k -y -vsync 1 -t 12 "(1-4)vid+origWAV.mp4"


  



  but the audio is slightly off now, and ends even further before the end of the video. Since it's really important to align audio and video precisely for this, how can I speed up the video to fit the exact duration of the audio or otherwise fix this issue ?

  


• mismatching process id from process execution. Why do they not match and how to fix script to get the correct pid ?

  26 février 2013, par buggedcom

  I'm running a script that executes ffmpeg and outputs stout to a temp file. Along side the output from ffmpeg I'm sending two tokens. one a marker for a failed execution. The other for marking when ffmpeg is completed. I'm trying to output the process id back to the executing script (which is php) however the process id being returned is not that of ffmpeg, rather the bash script.

  The script is as below.

  ((/opt/local/bin/ffmpeg -i '/Users/ollie/Sites/@Projects/PHPVideoToolkit/v2/git/examples/media/BigBuckBunny_320x180.mp4' -y -t '20' -strict 'experimental' -s '142x80' -aspect '16:9' -b:v '10000k' '/Users/ollie/Sites/@Projects/PHPVideoToolkit/v2/git/examples/output/test-1361797899.mp4' && echo '') || echo '' '') 2>&1 > '/Users/ollie/Sites/@Projects/PHPVideoToolkit/v2/git/examples/tmp/phpvideotoolkit_GmxT4T' 2>&1 & echo $!

  Example output from the script is as follows :

  [19] 19316

  However querying ps. The process id of ffmpeg is different. For example :

  Olivers-Mac-Pro:~ ollie$ ps
  
    PID TTY           TIME CMD
  
  19025 ttys002    0:00.00 -bash
  
  19026 ttys002    0:00.00 -bash
  
  19316 ttys002    0:00.00 -bash
  
  19317 ttys002    0:00.00 -bash
  
  19318 ttys002    0:46.56 /opt/local/bin/ffmpeg -i /Users/ollie/Sites/@Projects/PHPVideoToolkit/v2/git/examples/media/BigBuckBunny_320x180.mp4 -y -strict experimental -s 142x80 -aspect 16:9 -b:v 10000k /Users
  
    849 ttys003    0:00.12 -bash
  
   7558 ttys004    0:00.03 -bash

  You see that the process id returned by the script does not match the ffmpeg process id given by ps. Why is this and how can I ammend the original script to get the correct process id ?

• Revision 6c280c2299 : Adjust style to match Google Coding Style a little more closely. Most of these

  1er novembre 2012, par Ronald S. Bultje

  Changed Paths : Modify /vp8/common/arm/arm_systemdependent.c Modify /vp8/common/debugmodes.c Modify /vp8/common/entropymode.c Modify /vp8/common/entropymode.h Modify /vp8/common/extend.c Modify /vp8/common/extend.h Modify /vp8/common/filter.c (...)