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• Revision 704028d435 : Experimental rate control change. When the codec in VBR (or cq) mode hits its m

  7 octobre 2013, par Paul Wilkins

  Changed Paths :
   Modify /vp9/encoder/vp9_onyx_if.c

  
  
  Experimental rate control change.

  When the codec in VBR (or cq) mode hits its max q limits and is
  struggling to hit a target bandwidth, the bit target per frame collapses.

  In the first instance normal frames cap out at the maximum allowed
  Q and then the ARF and GFs do the same. This latter behavior is not
  generally desirable as GFs and ARFs are only effective from a quality
  and data rate perspective if they have at lease some level of -Q delta
  compared to the surrounding frames.

  In this patch I define a separate max Q for GFs and ARFs that is
  derived from but somewhat lower than that defined for normal frames.
  In effect there is a minimum Q delta that will always be available for
  GFs and ARFs regardless of the target rate and MAXQ setting.

  This may of course mean that the absolute lowest rate obtainable for
  a given clip is somewhat higher.

  Change-Id : I268868b28401900d0cd87e51e609cd3b784ab54a

• 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

• How do you get ffmpeg to convert a video, parse its thumbnail and then pass it back to Elgg in the file upload function ? [closed]

  22 janvier, par Orange

  I know my question is very specific, but I'm using the social media base (with WAMP) Elgg to create a Flash-based video sharing site for older browsers and computers and I was wondering how does one set up ffmpeg and Elgg in tandem so Elgg gets both a thumbnail and a video converted to FLV from an MP4 file someone uploads from their computer.

  


  I'm using Elgg 1.9 and ffmpeg-20130314.

  


  I couldn't figure out how to inject ffmpeg into Elgg so I tried duplicating the upload form so it had two file upload buttons (second one for thumbnail image) but this broke the site and made a blank undeletable video.