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• FFmpeg chromakey libavfilter using C-API - key/replace green with alpha transparency

  3 juin 2020, par ZeroDefect

  I'm trying to use the FFmpeg chromakey libavfilter (via the C-API using C++17) to key some green pixels in a YUVA422p image and replace them with alpha transparency.

  



  Now, I setup/initialise the graph, connect the filters, and push through a frame ; however, the output frame appears unchanged. I suspect one of my configuration parameters is incorrect, but I'm really unsure. After having read the pertinent documentation, I still don't understand the problem.

  



  I have published a (minimal) code sample in github - https://github.com/zerodefect/chromakey_test. I have tried to keep the code sample as brief as possible but it is still a bit lengthy.

  



  The code sample includes a sample image (green_screen.png) for the purposes of testing.

  



  To run the application, the following parameters are required :

  



  


  ./cb_chroma_key_test ./green_screen.png [OUTPUT_PATH]

  


  



  The application dumps out a PLANAR image at YUV422p which I then load in via rawpixels.net - a brilliant little online utility to view raw image data (packed or planar).

  



  My avfilter graph consists of :

  



  


  buffersrc -> format -> chromakey -> buffersink

  


  



  The format filter is taking the RGBA (packed) format and converting it to YUVA422 planar.

  



  

  • GCC 8.4

  


  • Ubuntu 18.04

  


  • FFmpeg 4.2

  


  


• Streaming Webcam Over LAN : HTML5 Video Element Not Loading

  27 novembre 2023, par Franck Freiburger

  I am currently working on a project where I aim to stream my webcam over my LAN and read the stream in an HTML5 video element with minimal setup. My setup involves a server (192.168.0.1 dev/video0 -> ffmpeg) and a client (192.168.0.2 html5 browser). I am using ffmpeg with the codec set to h264.

  


  Here is the ffmpeg command I am using :

  


  ffmpeg -f video4linux2 -i /dev/video0
  -an -c:v libx264 -b:v 1024k -video_size 800x600 -pix_fmt yuv420p -preset ultrafast
  -tune zerolatency -g 16 -keyint_min 16 -f mpegts pipe:1


  


  This command is spawned by a simple Node.js server that shares this stream without any transformation (just pipe ffpmeg stream to each incoming connection).

  


  When I use vlc or ffplay with the following command, it works very well :

  


  ffplay -fflags nobuffer -flags low_delay -probesize 32 -analyzeduration 0 -framedrop http://192.168.0.1:3000/stream


  


  I can even run multiple instances of ffplay and the video is properly played. However, when I try to use the HTML5 element like this :

  


  <video src="http://127.0.0.1:3000/stream" type="video/mp4"></video>&#xA;

  


  The video seems to "load forever" without any error, nothing suspect in chrome://media-internals. I can see in the network tab that the network is reading the stream, but the video does not play (got same result using hljs and videojs).

  


  

  


  I am looking for help to understand :

  


  

  • What is wrong with the <video></video> element in this context ?

  


  • Is there a better approach to achieve this ?

  


  


  Any help or guidance would be greatly appreciated.

  


• lavu/riscv : CPU flag for the Zbb extension

  2 octobre 2022, par Rémi Denis-Courmont

  lavu/riscv : CPU flag for the Zbb extension
  Unfortunately, it is common, and will remain so, that the Bit
  
  manipulations are not enabled at compilation time. This is an official
  
  policy for Debian ports in general (though they do not support RISC-V
  
  officially as of yet) to stick to the minimal target baseline, which
  
  does not include the B extension or even its Zbb subset.
  For inline helpers (CPOP, REV8), compiler builtins (CTZ, CLZ) or
  
  even plain C code (MIN, MAX, MINU, MAXU), run-time detection seems
  
  impractical. But at least it can work for the byte-swap DSP functions.
  

  • [DH] libavutil/cpu.c
  • [DH] libavutil/cpu.h
  • [DH] libavutil/riscv/cpu.c
  • [DH] tests/checkasm/checkasm.c