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• FFMPEG - 4K HDR - MPEG - BIG FILE convert

  8 mars 2018, par Ian Lodanko

  I would like to ask how through ffmpeg to achieve the smallest file size and yet keep the best quality [LIKE Youtube convert].

  Currently used :

  ffmpeg -i "/home/sampe_4K_HDR.mkv" -map 0:00 -c:v libx264 -preset ultrafast -b:v 66718k -pix_fmt yuv420p10le -x264-params "colorprim=bt2020:transfer=smpte2084:colormatrix=bt2020nc" -crf 18 -c:a libfdk_aac -profile:v baseline -level 3.0 "/home/sampe_4K_HDR.mp4"

  But the size of the video after conversion is very large, I would like to preserve as much as possible the quality of the original video and get the smallest possible video size.

  Could you please advise ? Write some examples of how to get better with smaller sizes ? Thank you in advance and I apologize for my English in advance.

• How to get frames from HDR video in scRGB color space ?

  5 mars 2018, par Виталий Синявский

  I want to create a simple video player that will show HDR video on HDR TV. For example, this "LG Chess HDR" video. It is encoded with HEVC, its bit depth is 10 bit, pixel format is YUV420P10LE and it has metadata abount BT2020 color space and PQ transfer function.

  In this NVIDIA article I found the next :

  The display driver takes the scRGB back buffer, and converts it to the
  standard expected by the display presently connected. In general, this
  means converting the color space from sRGB primaries to BT. 2020
  primaries, scaling to an appropriate level, and encoding with a
  mechanism like PQ. Also, possibly performing conversions like RGB to
  YCC if that display connection requires it.

  It means that my player should render pixels in the scRGB color space (linear encoding, sRGB primaries, full range is -0.5 through just less than +7.5). So I need to get frames from the source video in this color space somehow, preferably in FP16 pixel format (half float, 16 bits per one color channel). I come to the following simple pipeline to render videos to HDR :

  source HDR video in BT2020 color space with applied PQ -> [some video library] -> 
  
  -> video frames with colors in scRGB color space -> [my program] ->
  
  -> rendered video on HDR TV with applied conversions by display driver

  I’m trying to use FFmpeg as this library and do not understand how to get frames from the source HDR video in scRGB color space.

  I use sws_scale FFmpeg method now to get frames and know about filters API. But I did not found any information and help about how to transparantly get frames in scRGB using these functionality without parsing metadata for all source videos and create custom video filters for them.

  Please, tell me what I can do to get frames in the scRGB color space using FFmpeg. Can someone tell other libraries with which I can do it ?

• correct way to download a mp4 [Audio only] file as a mp3 file via php

  3 février 2018, par Kapil

  I am asking this question because i found it impossible as far my knowledge stands. However i believe here on stackoverflow a lot of genius persons visits so maybe someone can give a good advice / trick.

  My problem is, I am downloading a audio/mp4 file of youtube hosted on googlevideo.com’s server.

  My PHP code for this purpose :
  $mp3path is url of video

  header('Content-Description: File Transfer');
  
  if(strpos($mp3path, "https://") === false) {
  
      header('Content-length: ' . size($mp3path)); //size is custom function
  
  } 
  
      header("Content-Type: audio/MP4A-LATM, audio/MP4A, audio/m4a, audio/mp4, audio/mp4a, audio/mp4-audio, audio/mpeg"); 
  
      header('Content-Type: application/force-download');
  
      header("Accept-Ranges: bytes");
  
      header('Content-Transfer-Encoding: binary'); 
  
      header('Content-disposition: attachment; filename="'.$title.'.mp3"'); 
  
      header('Connection: Keep-Alive');
  
      header('Expires: 0');
  
      header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
  
      header('Last-Modified: ' . gmdate('D, d M Y H:i:s', time()) . ' GMT');
  
      header("Cache-Control: private", false);
  
      header('Pragma: no-cache');
  
      readfile($mp3path);
  
      exit;

  I can download this audio file but few mp3 players are not able to play it when i did some research on by using mp3val [mp3val.sourceforge.net]. I found this file do not contain sample-rate, bit-rate or some other required codecs inside the file.
  Error received from mp3val : Unknown file format

  I know one possible way of doing this which is ffmpeg but i am looking for a less time consuming option of doing this because first ffmpeg download the whole file and then convert it to mp3 and save it on server. It takes a lot of time.

  I am looking for a easiest solution in which, i dont want to save the whole file on my server. I want to call this file from remote server and want to add sample rate, bit-rate in the file and then just somehow with php i want to start download on browser.

  All i mean to say i need a faster solution. I have seen 2 yt to mp3 converter, They are doing the same thing, giving instant download. i dont know how ?

  Please if you think its a stupid question or not possible then dont report to stackoverflow. I am trying to figure it out that’s why i am asking this question here. I hope you’ll understand my curiosity.

  Thanks,