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• Inconsistent behavior when placing adjacent video overlays

  24 juillet 2023, par abingham

  This script uses ffmpeg to overlay a red [1] and blue [2] stream atop a yellow [0] stream. The intent is that the red stream will be exactly adjacent to the blue stream ; at frame 1731 the output video should transition immediately from pure red to pure blue :

  


  # These values result in a blank frame where the videos join at around 58s
LENGTH=1800
SPLIT_AT=1731

# These values work just fine.
# LENGTH=1800
# SPLIT_AT=2

ffmpeg \
-f lavfi -r 30 -i "color=c=yellow:s=1920x1080" \
-f lavfi -r 30 -i "color=c=990000:s=1920x1080" \
-f lavfi -r 30 -i "color=c=000099:s=1920x1080" \
-filter_complex \
"[1]concat=n=1[red_concat];"\
"[red_concat]tpad=start=0[red_pad];"\
"[0][red_pad]overlay=enable=between(n\,0\,$SPLIT_AT):eof_action=repeat[red_overlay];"\
"[2]concat=n=1[blue_concat];"\
"[blue_concat]tpad=start=$SPLIT_AT[blue_pad];"\
"[red_overlay][blue_pad]overlay=enable=between(n\,$SPLIT_AT\,$LENGTH):eof_action=repeat[blue_overlay];"\
"[blue_overlay]trim=end_frame=$LENGTH[full];" \
 -map "[full]" video.mp4 -y


  


  However, what I see is that there is a single black frame between the pure red and pure blue. This black seems to be coming from the frames that tpad adds.

  


  What I don't understand is why I'm seeing that black frame. As far as I can tell, my uses of tpad and overlay/enable-between should produce a seamless transition from red to blue. And indeed, if I change the SPLIT_AT value to almost anything else I get exactly that ; the value 1731 is "special" in some way.

  


  Can anyone explain what's going on ? Maybe more importantly, can anyone reproduce this problem ?

  


  My first thought was that I've got some form of fencepost error in how I'm using tpad or enable-between. However, that doesn't explain why the script works for most values but not 1731. This difference in results feels like there's a rounding error somewhere, but since I'm dealing purely in terms of integer frame numbers, I don't see how I could be introducing them.

  


  A few notes :

  


  


  • This is a drastically reduced example from a larger video compositing system. Things like the use of concat may appear unnecessary, but they're representative of what the larger system is doing.

    


  


  • I'm using ffmpeg-6.0 installed via homebrew on an M1 macbook

    


  


  


• Why is ffmpeg's hstack so much slower than overlay and pad ?

  27 janvier 2021, par cgenco

  I'm using ffmpeg to stitch together two videos of people chatting into a video with each of them side-by-side, like this :

  


  

  


  Here's the command I'm currently using to get this done, which runs at 2.5x on my 13" M1 MacBook Pro :

  


  ffmpeg -y -i left.mp4 -i right.mp4 -filter_complex "
  [0:v] crop=w=in_w/2 [croppedLeft];
  [1:v][1:v] overlay=x=overlay_w/4 [shiftedRight];
  [shiftedRight][croppedLeft] overlay [vout];
  [0:a][1:a] amix [aout]
" -map "[vout]" -map "[aout]" -ac 2 out.mp4


  


  This command crops the left video to half of its original width (cropping so the video is centered), then shifts the right video a quarter of its width to the right, then overlays the left video on the left half of the output merged with the shifted right video.

  


  One day on my weekly fun-time read-through the FFmpeg filters documentation I stumbled on a filter named hstack, which is described as being "faster than using overlay and pad filter to create same output."

  


  My ex wife can affirm that there are few higher priorities in my life than going faster, so I altered my ffmpeg script to use hstack instead of two overlays :

  


  ffmpeg -y -i left.mp4 -i right.mp4 -filter_complex "
  [0:v] crop=w=in_w/2 [croppedLeft];
  [1:v] crop=w=in_w/2 [croppedRight];
  [croppedLeft][croppedRight] vstack [vout];
  [0:a][1:a] amix [aout]
" -map "[vout]" -map "[aout]" -ac 2 out.mp4


  


  ...but that command runs painfully slowly, like 0.1x. It takes multiple minutes to render a single second.

  


  So uhhh what's going on here ? Why is hstack taking so long when it's supposed to be faster ?

  


  I've tried this on both the M1 native build from OSXExperts (version N-99816-g3da35b7) and the standard ffmpeg from brew and hstack is just as slow on each.

  


• Processing3 get "Error=2 No such file or directory" with a file that actually doesn't exist at the first place

  29 octobre 2016, par Tuang Pingfavilunda

  I cannot figure it out what happen to my Processing file. I am trying to use VideoExport library and my Macbook Pro cannot play it, but the Mac-mini is able to do so.

  Before the error happened it is another error=13 permission denied thing, so I messed in the terminal for a while with chmod 777 and finding the file with ls. I don’t know if that may be the reason that caused this happen. FYI, I also installed ffmpeg already.

  And this is the full error :

      java.io.IOException: Cannot run program "/Users/Tuang/Desktop/DMA_WORKS/Work1_Facial Muscles/Cam_Rec/sketch_161027a/sketch_161027a.pde": error=2, No such file or directory
  
      at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
  
      at com.hamoid.VideoExport.startFfmpeg(Unknown Source)
  
      at com.hamoid.VideoExport.initialize(Unknown Source)
  
      at com.hamoid.VideoExport.saveFrame(Unknown Source)
  
      at Basic.draw(Basic.java:32)
  
      at processing.core.PApplet.handleDraw(PApplet.java:2412)
  
      at processing.awt.PSurfaceAWT$12.callDraw(PSurfaceAWT.java:1540)
  
      at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:316)
  
  Caused by: java.io.IOException: error=2, No such file or directory
  
      at java.lang.UNIXProcess.forkAndExec(Native Method)
  
      at java.lang.UNIXProcess.<init>(UNIXProcess.java:247)
  
      at java.lang.ProcessImpl.start(ProcessImpl.java:134)
  
      at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
  
      ... 7 more
  
  VideoExport error: Ffmpeg failed. Study /Users/Tuang/Desktop/DMA_WORKS/Work1_Facial_Muscles/Camera_Recorder/Basic/basic.mp4.txt for more details.
  
  Could not run the sketch (Target VM failed to initialize).
  
  For more information, read revisions.txt and Help → Troubleshooting.
  
  </init>

  ---

  1) The java.io.IOException : trying to call "/Work1_Facial Muscles/Cam_Rec/sketch_161027a/sketch_161027a.pde" which doesn’t exist for real. It is gone for a long time but seems like the program stuck here.

  2) "basic" is a file name from the Example of the Library. I just use it to test. Surprisingly, Every files that have been saved and changed the name still get the java.io.IOException’s error of the missing sketch_161027a.pde file.

  ---

  What I have done :
  1 I have already done the Homebrew thing to install ffmpeg.
  2 I deleted everything of Processing and reinstall it again.

  Any suggestion ?