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• lavc : fix and extend AVCodecContext.get_format doxy

  17 juin 2021, par Anton Khirnov

  lavc : fix and extend AVCodecContext.get_format doxy
  Remove some incorrect (or at least misleading) statements, such as the
  
  formats being ordered by quality, or the first format being the native
  
  one. Neither of those are true for hardware acceleration, which is the
  
  main use of this callback.
  

  • [DH] libavcodec/avcodec.h

• Is there a way to apply a curve bend in ffmpeg ?

  25 mars 2020, par stevendesu

  I have four cameras each feeding me a different portion of a basketball court. Due to the slight offset of the cameras physical locations and lens distortion around the edges of the camera, I cannot simply stitch the videos together without some kind of correction.

  I’ve looked into ffmpeg’s perspective filter, as well as the lenscorrection filter. In the former case it was only able to create a trapezoid, not the curved image I want. In the latter case using negative values to k1 and k2 seemed to be heading in the right direction, but it either disorted the top and bottom of the image to the point of being nonsensical noise, or it zoomed in to the image so much that I lost important details.

  For the sample picture below, ultimately I want the midcourt line (the blue vertical line on the right side) to be vertical, and I want the mess of wires on the white desk at the bottom to remain visible and identifiable.

  Given a video which looks like the following :

  

  I wish to produce something like the following :

  

  This image was made using the "Curve Bend" filter in GIMP, but I just eye-balled it - so it’s not perfect. Ideally once I get the exact parameters the midcourt line will be perfectly vertical

  When using the lenscorrection filter, no values for k1 and k2 seemed to get the effect I want :

  Negative k1, negative k2 :

  

  Negative k1, positive k2 :

  

  Positive k1, negative k2 :

  

  Positive k1, positive k2 :

  

  In general :

  • negative / negative distorted the image beyond recognition
  • negative / positive looked alright, but the midcourt line was off the screen and it wasn’t clear if any distortion had been applied
  • positive / negative looked the best, but while the top and bottom curved in the middle of the left and right actually bulged out, leaving the midcourt line distorted
  • positive / positive was the opposite of the desired effect

• FFMPEG : Add a fixed size image on a video, regardless of the video width & height (resolution)

  11 mars 2017, par Drupalist

  This is my code that adds an image to videos, running via PHP :

  exec('ffmpeg -i input.mp4 -i logo.png -filter_complex 
  
  "[0:v][1:v] overlay=10:10"  -pix_fmt yuv420p -c:a copy output.mp4');

  It works well but the problem is, the image is scaled down or up, up on the video resolution. For example in the following images the logo width is 50px but videos resolution are different :

  

  and this one

  

  How can I prevent the image from scaling down/up ?

  ---

  Update

  Thanks to Mulvya, he proposed these codes

  ffmpeg -i input.mp4 -i logo.png -filter_complex 
  
  "[1:v][0:v]scale2ref=(W/H)*ih/8:ih/8[wm][base];[base][wm]overlay=10:10"
  
  -pix_fmt yuv420p -c:a copy output.mp4

  and

  ffmpeg -i input.mp4 -i logo.png -filter_complex 
  
  "[1:v][0:v]scale2ref=(W/H)*ih/8:ih/8[wm][base];[wm]setsar=1[wmsar];
  
  [base][wmsar]overlay=10:10"
  
  -pix_fmt yuv420p -c:a copy output.mp4

  that works very well, but it doesn’t keep the logo aspect ratio.
  I tried this code on two videos with different resolution and this is the result

  

  and this one

  

  Is it possible to improve this solution ?