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• aacenc : reorder coding tools

  2 septembre 2015, par Rostislav Pehlivanov

  aacenc : reorder coding tools
  This commit reorders the coding tools such that they’re doing what
  
  the decoder does in reverse order. The very first thing the decoder
  
  does is to decode M/S stereo if that’s signalled, then prediction,
  
  IS, and finally TNS and PNS in another function.
  
  adjust_frame_information()’s application of IS and M/S was taken
  
  out into two separate functions since prediction doesn’t expect
  
  to get the raw coefficients but rathe the coefficients at that
  
  part of the encoding process.
  The results show a much better PSNR when any combination of
  
  Intensity Stereo, Mid/Side stereo and Prediction is used, which
  
  is a sign of an increased encoder efficiency as well as the fact
  
  that the decoder gets what it expects.
  Otherwise, with only IS, PNS or prediction there are neither
  
  regressions nor improvements except in the case of IS, which
  
  now by itself (or with PNS) is less prone to artifacts. Enabling
  
  M/S (using stereo_mode) as well will also reduce stereo artifacts
  
  induced by IS, so in the very near future M/S may be enabled
  
  by default.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aacenc.c

• Higher quality of JPEG frames extracted with FFMPEG from MP4 video [on hold]

  5 juin 2019, par 2006pmach

  I got a 4k mp4 video file and my goal is to extract the individual frames. Unfortunately, the video is quite big 10GB and storing all the frames lossless (e.g. using png, results in 12MB per frame) is not an option. Therefore, I tired to save directly JPEG images. For me quality is more important than a small file size around 1MB would be good.
  To do so I used FFMPEG as follows :

  ffmpeg -ss 00:04:52 -i video.MP4 -qscale:v $quality -frames:v 1 output-$quality.jpg

  I tried the full range from 2 to 31 for $quality and obtained the blue curve in the plot (PSNR vs. File size)

  Additionally, I extracted the frame and saved it as PNG and used convert from ImageMagick to compress the PNG file as follows :

  convert -quality $quality% frame.png output-$quality.jpg

  Again I tried the full range for $quality from 10 to 100 and obtained the orange line in the plot (The highest quality is 50dB but uses 6MB, so I only show the results up to 2MB).

  Now, my questions are as follows. Why is the quality of ffmpeg that much worse than when using ImageMagick ? Is it possible to increase the quality of the JPEG frames using ffmpeg directly or do I need to go via the PNG and then to JPEG. The later method is somehow suboptimal because it requires storing the png and will be much slower. Any suggestions ? My guess is that ffmpeg trades quality vs. speed...

  

• FFmpeg : How do i use this script to concatenate incoming segments

  5 juillet 2017, par NGage

  I’d like to use this script but i don’t know how it should be applied. I was going to use it for encoding tv-shows and be able to start encoding as i had cut out the first segment.

  According to the ffmpeg-wiki (where i found the script) it says : "Concatenation becomes troublesome, if next clip for concatenation does not exist at the moment, because decoding won’t start until the whole list is read. However, it is possible to refer another list at the end of the current list :"

  Bear in mind that i dont know to much about bash

  #!/bin/bash
  
  
  
  fn_concat_init() {
  
  echo "fn_concat_init"
  
  concat_pls=`mktemp -u -p . concat.XXXXXXXXXX.txt`
  
  concat_pls="${concat_pls#./}"
  
  echo "concat_pls=${concat_pls:?}"
  
  mkfifo "${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_feed() {
  
  echo "fn_concat_feed ${1:?}"
  
  {
  
      >&2 echo "removing ${concat_pls:?}"
  
      rm "${concat_pls:?}"
  
      concat_pls=
  
      >&2 fn_concat_init
  
      echo 'ffconcat version 1.0'
  
      echo "file '${1:?}'"
  
      echo "file '${concat_pls:?}'"
  
  } >"${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_end() {
  
  echo "fn_concat_end"
  
  {
  
      >&2 echo "removing ${concat_pls:?}"
  
      rm "${concat_pls:?}"
  
      # not writing header.
  
  } >"${concat_pls:?}"
  
  echo
  
  }
  
  
  
  fn_concat_init
  
  
  
  echo "launching ffmpeg ... all.mkv"
  
  timeout 60s ffmpeg -y -re -loglevel warning -i "${concat_pls:?}" -pix_fmt 
  
  yuv422p all.mkv &
  
  
  
  ffplaypid=$!
  
  
  
  
  
  echo "generating some test data..."
  
  i=0; for c in red yellow green blue; do
  
  ffmpeg -loglevel warning -y -f lavfi -i testsrc=s=720x576:r=12:d=4 -pix_fmt 
  
  yuv422p -vf "drawbox=w=50:h=w:t=w:c=${c:?}" test$i.mkv
  
  fn_concat_feed test$i.mkv
  
  ((i++));
  
  echo
  
  done
  
  echo "done"
  
  
  
  fn_concat_end
  
  
  
  wait "${ffplaypid:?}"
  
  
  
  echo "done encoding all.mkv"