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• avcodec/sheervideo : Reduce the size of static arrays

  10 octobre 2020, par Andreas Rheinhardt

  avcodec/sheervideo : Reduce the size of static arrays
  The SheerVideo decoder uses VLC tables which are currently stored in
  
  large arrays that contain the length of each leaf of the corresponding
  
  tree from left to right, taking 15.5KB of space. But all these arrays
  
  follow a common pattern : First the entries are ascending and then they
  
  are descending with lots of successive entries have the same value.
  
  Therefore it makes sense to use a run-length encoding to store them, as
  
  this commit does. Notice that the length 16 has to be treated specially
  
  because there are arrays with more than 256 consecutive entries with
  
  value 16 and because the length of the entries start to descend from
  
  this length onward.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/sheervideo.c
  • [DH] libavcodec/sheervideodata.h

• Reduce write time in stdin stream

  20 décembre 2020, par گورو سینی

  I'm trying to record the web page with puppeteer. For that I'm using the same approach as puppeteer-recorder ie taking the screenshot for each frame and writing to the spawned ffmpeg's stdin stream with slight modifications.

  


  The average time taken for screenshot per frame comes between 1-2ms but the average time to write the screenshot data into stream comes to be 290-300ms per frame.

  


  const ffmpeg = spawn(ffmpegPath, ffmpegArgs(30));

for (let i = 1; i <= totalFrames; i++) {
  let screenshot = await page.screenshot({ omitBackground: true });  --> 1ms
  await write(ffmpeg.stdin, screenshot);                             --> 290ms
}

ffmpeg.stdin.end();


const write = (stream, buffer) =>
 new Promise((resolve, reject) => {
   stream.write(buffer, error => {
     if (error) reject(error);
     else resolve();
 });
});


const ffmpegArgs = fps => [
  '-y', '-f', 'image2pipe',
  '-r', `${+fps}`,
  '-i', '-',
  '-c:v', 'libx264',
  '-auto-alt-ref', '0',
  '-s:v', '1280x720',
  '-crf', '20',
  '-pix_fmt', 'yuv420p',
  '-metadata:s:v:0', 'alpha_mode="1"',
  '-tune', 'stillimage', 
  '-movflags', '+faststart', 'output.avi'
];


  


  Is there any way to reduce the time taken while writing ? Thanks.

  


• FFmpeg taking too long to process video (x264)

  19 avril 2022, par hugger

  I am succesfully processing my video into x264. I am happy with the output and file size I am generating, but the video seems to take as long as the video is to process.

  


  For example, if the video is 10 seconds long, it will take 10 seconds to process the video, etc...

  


  Even if I put -crf 50, it will take the same time. I find this odd behaviour.

  


  Note : I am using FFmpeg with FFmpegKit (React Native) : https://github.com/tanersener/ffmpeg-kit

  


  I am using full-gpl in order to be able to encode to x264. I am not sure what is wrong here or if this is normal behaviour ?

  


  Here is my FFmpeg command I am executing :

  


  `-y -i ${media.path} -c:v libx264 -preset veryfast -tune fastdecode -crf 20 -vf "crop=1350:1080, scale=960:780" -c:a copy -movflags faststart ${path}`


  


  I appreciate all the help I can get here to speed this up / fix this issue.

  


  Cheers !