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• FFMpeg add drop shadow to a video

  13 juillet 2022, par Francesco Galgani

  I have this example video, recorded by Kazam :
https://user-images.githubusercontent.com/1997316/178513325-98513d4c-49d4-4a45-bcb2-196e8a76fa5f.mp4

  


  It's a 1022x728 video.

  


  I need to add a drop shadow identical to the one generated by the "Drop shadow (legacy)" filter of Gimp with the default settings. So, I generated with Gimp a PNG containing only the drop shadow. It's a 1052x758 image :

  


  

  


  Now I want to put the video over the image to get a new video with the drop shadow. The wanted effect for the first frame is :

  


  

  


  So, the video must be placed over the image. The top-left corner of the video must be in the position 11x11 of the background image.

  


  How can I achieve this result ?

  


  I tried without success the following command. What's wrong ?

  


  ffmpeg -i shadow.png -i example.mp4 -filter_complex "[0:v][1:v] overlay=11:11'" -pix_fmt yuv420p output.mp4


  


  About the transparency of the PNG background image, if it can't be maintained, then it's okay for the shadow to be on a white background. Otherwise, if it can be maintained by using an animated GIF as the output format, it is better.

  


• x86 : ac3dsp : Remove 3dnow version of ff_ac3_extract_exponents

  26 avril 2013, par Diego Biurrun

  x86 : ac3dsp : Remove 3dnow version of ff_ac3_extract_exponents
  The function requires increasing the fuzz factor for the ac3/eac3 encode
  
  tests and even so makes fate fail. It only provides a slight encoding
  
  speedup for legacy CPUs that do not support SS2. Thus its benefit is not
  
  worth the trouble it creates and fixing it would be a waste of time.
  

  • [DBH] libavcodec/x86/ac3dsp.asm
  • [DBH] libavcodec/x86/ac3dsp_init.c
  • [DBH] tests/fate/ac3.mak

• QOpenGLWidget video rendering perfomance in multiple processes

  24 novembre 2018, par MasterAler

  My problem may seem vague without code, but it actually isn’t.

  So, there I’ve got an almost properly-working widget, which renders video frames.

  Qt 5.10 and QOpenGLWidget subclassing worked fine, I didn’t make any sophisticated optimizations — there are two textures and a couple of shaders, converting YUV pixel format to RGB — glTexImage2D() + shaders, no buffers.

  Video frames are obtained from FFMPEG, it shows great performance due to hardware acceleration... when there is only one video window.

  The piece of software is a "video wall" — multiple independent video windows on the same screen. Of course, multi-threading would be the preferred solution, but legacy holds for now, I can’t change it.

  So, 1 window with Full HD video consumes 2% CPU & 8-10% GPU regardless of the size of the window. But 7-10 similar windows, launched from the same executable at the same time consume almost all the CPU. My math says that 2 x 8 != 100...

  My best guesses are :

  • This is a ffmpeg decoder issue, hardware acceleration still is not magic, some hardware pipeline stalls
  • 7-8-9 independent OpenGL contexts cost a lot more than 1 cost x N
  • I’m not using PUBO or some other complex techniques to improve OpenGL rendering. It still explains nothing, but at least it is a guess

  The behavior is the same on Ubuntu, where decoding uses different codec (I mean that using GPU accelerated or CPU accelerated codecs makes no difference !), so, it makes more probable that I’m missing something about OpenGL... or not, because launching 6-7 Qt examples with dynamic textures shows normal growth of CPU usages — it is approximately a sum for the number of windows.

  Anyway, it becomes quite tricky for me to profile the case, so I hope someone could have been solving the similar problem before and could share his experience with me. I’d be appreciated for any ideas, how to deal with the described riddle.

  I can add any pieces of code if that helps.