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• How to know the delay of frames between 2 videos, to sync an audio from video 1 to video 2 ?

  8 janvier 2021, par jaimepm

  world.

  


  I have many videos that I want to compare one-to-one to check if they are the same, and get from there the delay of frames, let's say. What I do now is opening both video files with virtualdub and checking manually at the beginning of video 1 that a given frame is at position, i.e., 4325. Then I check video 2 to see the position of the same frame, i.e., 5500. That would make a delay of +1175 frames. Then I check at the end of the video 1 another given frame, position let's say 183038. I check too the video 2 (imagine the position is 184213) and I calculate the difference, again +1175 : eureka, same video !
The frame I chose to compare aren't exactly random, it must be one that I know it is exactly one I can compare to (for example, a scene change, an explosion that appears from one frame to another, a dark frame after a lighten one...) and I always try to check for the first comparison frames within the first 10000 positions and for the second check I take at the end.
What I do next is to convert the audio from video 1 to video 2 calculating the number of ms needed, but I don't need help with that. I'd love to automatize the comparison so I just have to select video 1 and video 2, nothing else, that way I could forget forever virtualdub and save a lot of time.

  


  I'm tagging this post as powershell too because I'm making a script where at the moment I have to introduce the delay between frames (after comparing manually) myself. It would be perfect that I could add this at the beginning of the script.

  


  Thanks !

  


• FFMPEG : How to overlay a large size png on jpg [closed]

  21 juin 2022, par Yoav Mor

  I'm trying to use ffmpeg to achieve the following :
x.jpg = a file that is 540x540 in size.
Gradient.png = a 540x960 image that has a gradient of semi transparency (which starts with dark blue with no transparency in the top and then gradually becomes transparent in the bottom)
example of Gradient.png attached

  


  The goal is to end up with a jpg that is 540x960, where x.jpg is in the bottom 540x540 of the frame and the Gradient.png is laid on top of it. Because Gradient.png is larger, this seems to pose a problem.

  


  I tried :

  


  ffmpeg.exe -i x.jpg -i Gradient.png -filter_complex overlay=0:480 -c:v png -pix_fmt rgba out.png


  


  Which just creates a 540x540 frame, so doesn't work. Feels close though. If I new how to enlarge the "canvas" this could have maybe worked.

  


  I tried.

  


  ffmpeg.exe -i Gradient.png -i x.jpg -filter_complex overlay=0:480 -c:v png -pix_fmt rgba out.png


  


  Which does create a 540x960 frame but Gradient.png is not on top of 1.jpg, the opposite is happening here, so I don't get the effect of the semi transparency shown on top of x.jpg like I need.

  


  Any help will be highly appreciated

  


  Edit :
I was able to do it in 2 steps.
ffmpeg -i x.jpg -vf "scale=540:960:force_original_aspect_ratio=decrease,pad=540:960 :(ow-iw)/2 :(oh-ih)" -c:v png -pix_fmt rgba out.jpg
ffmpeg -i out.jpg -i Gradient.png -filter_complex overlay=0:0 OUT2.jpg

  


  If someone can come up with a way to do it in one step, it'll be great.

  


• Started Programming Young

  6 septembre 2011, par Multimedia Mike — Programming

  I have some of the strangest memories of my struggles to jump into computer programming.

  Back To BASIC
  I remember doing some Logo programming on Apple II computers at school in 5th grade (1987 timeframe). But that was mostly driving turtle graphics. Then I remember doing some TRS-80 BASIC in 7th grade, circa 1989. Emboldened by what very little I had learned in perhaps the week or 2 we took in a science class to do this, I tried a little GW-BASIC on my family’s “IBM-PC compatible” computer (they were still called that back then). I still remember what my first program consisted of. Even back then I was interested in manipulating graphics and color on a computer screen. Thus :

  10 color 1
  20 print "This is color 1"
  30 color 2
  40 print "This is color 2"
  ...
  

  And so on through 15 colors. Hey, it did the job– it demonstrated the 15 different colors you could set in text mode.

  What’s FOR For ?
  That 7th grade computer unit in science class wasn’t very thick on computer science details. I recall working with a lab partner to transcribe code listings into a computer (and also saving my work to a storage cassette). We also developed form processing programs that would print instructions to input text followed by an “INPUT I$” statement to obtain the user’s output.

  I remember there was some situation where we needed a brief delay between input and printing. The teacher told us to use a construct of the form :

  10 FOR I = 1 TO 20000
  20 NEXT I
  

  We had to calibrate the number based on our empirical assessment of how long it lasted but I recall that the number couldn’t be much higher than about 32000, for reasons that would become clearer much later.

  Imagine my confusion when I would read and try to comprehend BASIC program code I would find in magazines. I would of course see that FOR..NEXT construct all over the place but obviously not in the context of introducing deliberate execution delays. Indeed, my understanding of one of the fundamental building blocks of computer programming — iteration — was completely skewed because of this early lesson.

  Refactoring
  Somewhere along the line, I figured out that the FOR..NEXT could be used to do the same thing a bunch of times, possibly with different values. A few years after I had written that color program, I found it again and realized that I could write it as :

  10 for I = 1 to 15
  20 color I
  30 print I
  40 next I
  

  It still took me a few more years to sort out the meaning of WHILE..WEND, though.