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• RGB-frame encoding - FFmpeg/libav

  4 février 2014, par learner

  I am learning video encoding & decoding in FFmpeg. I tried the code sample on this page (only the video encoding & decoding part). Here the dummy image being created is in YCbCr format. How do I achieve similar encoding by creating RGB frames ? I am stuck at :

  Firstly, how to create this RGB dummy frame ?

  Secondly, how to encode it ? Which codec to use ? Most of them work with YUV420p only...

  EDIT : I have a YCbCr encoder and decoder as given on the this page. The thing is, I have RGB frame-sequence in my database and I need to encode it. But the encoder is for YCbCr. So, I am wondering to convert RGB frames to YCbCr (or YUV420P) somehow and then encode them.
  At decoding end, I get decoded YCbCr frames and I convert them back to RGB. How to go ahead with it ?

  I did try the swscontext thing, but the converted frames lose color information and also scaling errors. I thought of doing it manually using two for loops and colorspace conversion formulae
  but I am not able to access individual pixel of a frame using FFmpeg/libav library ! Like in OpenCV we can easily access it with something like : Mat img(x,y) but no such thing here ! I am totally a newcomer to this area...

  Someone can help me ?

  Many Thanks !

• x86/tx_float : remove vgatherdpd usage

  20 mai 2022, par Lynne

  x86/tx_float : remove vgatherdpd usage
  Its performance loss ranges from either being just as fast as individual loads
  
  (Skylake), a few percent slower (Alderlake), 8% slower (Zen 3), to completely
  
  disasterous (older/other CPUs).
  Sadly, gathers never panned out fast on x86, even with the benefit of time and
  
  implementation experience.
  This also saves a register, as there's no need to fill out an additional
  
  register mask.
  Zen 3 (16384-point transform) :
  
  Before : 1561050 decicycles in           av_tx (fft),  131072 runs,      0 skips
  
  After :  1449621 decicycles in           av_tx (fft),  131072 runs,      0 skips
  Alderlake :
  
  2% slower on big transforms (65536), to 1% (131072), to a few percent for smaller
  
  sizes.
  

  • [DH] libavutil/x86/tx_float.asm
  • [DH] libavutil/x86/tx_float_init.c

• Android Java (ffmpeg-kit). Assistance(opinion) with combining 4 ffmpeg commands together

  26 novembre 2022, par D-MAN

  I have the following 4 ffmpeg commands. 1. adds a png frame(border) over the entire length of the video. 2. creates a boomerang effect. 3. adds an outro jpeg to the last 2 seconds of the video. 4. Adds an intro jpeg to the first 2 seconds of the video.(these commands work individually)

  


  My aim is to combine all of these individual commands into one command to create a complete edited video. The final video needs all these elements in one final edited video.

  


  Your assistance is greatly appreciated.

  


  /**
 *

 * (Middle overlay filter) String exe = "-i " + input_video_uri + " -framerate 60 -i " + frame + " -filter_complex [0]pad="+mVideoWidth+":"+mVideoHeight+":576:0[vid];[vid][1]overlay -c:a copy -vcodec mpeg4 -crf 0 -preset ultrafast -qscale 0 " + file2.getAbsolutePath();

 * (Boomerang effect) String exe = "-y -i " + input_video_uri + " -filter_complex [0]reverse[r];[0][r][0]concat=n=3,setpts=0.5*PTS " + file2.getAbsolutePath();

 * (Put image at end of video) String exe = "-i "+ input_video_uri +" -i "+ frame +" -filter_complex \"[0:v][1:v] overlay=0:0:enable='between(t,"+ (msec - 2 ) + ","+ msec+")'\" -pix_fmt yuv420p -c:a copy " + file2.getAbsolutePath();

 * (Put image at start of video) String exe = "-i "+ input_video_uri +" -i "+ frame +" -filter_complex \"[0:v][1:v] overlay=0:0:enable='between(t,0,2)'\" -pix_fmt yuv420p -c:a copy " + file2.getAbsolutePath();

 * */


  


  Being new to ffmpeg, I am limited in knowledge. However, I have tried '&&' which produced an unrecognized error from the ffmpeg library.