Recherche avancée

Sur d’autres sites (9980)

• calling ffmpeg from python in a loop

  22 juin 2018, par Steffen Lesch

  I am currently writing my first python script to split large audio files into smaller ones. (Splitting Albums into individual tracks) :

  import subprocess
  
  
  
  def genList():
  
      with open("commands.txt") as file:
  
          ffmpeg_template_str = 'ffmpeg -i audio.FLAC -acodec copy -ss START_TIME -to END_TIME LITTLE_FILE'
  
          lines = file.readlines()
  
          results = []
  
  
  
          for line in lines:
  
              argument_list = line.split(' ')
  
              result = ffmpeg_template_str
  
              results.append(result.replace('START_TIME', argument_list[0]).replace('END_TIME', argument_list[1]).replace('LITTLE_FILE', argument_list[2]))
  
      return results;
  
  
  
  def split():
  
      commands = genList()
  
      for command in commands:
  
          subprocess.call(command.split(' '))
  
  
  
  split()

  When i execute the script, many command line windows will pop up, but only the last delivers the desired result.

  So if i want to split an audio file into smaller files only the last split operation seems to executed correctly.

  Additionally if i dont use a for loop and just paste subprocess.call multiple times into the code it works just fine.

  subprocess.call(command1)
  
  subprocess.call(command2)
  
  subprocess.call(command3)

  Any help will be greatly appreciated.

• 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 Error : Pattern type 'glob' was selected but globbing is not support ed by this libavformat build

  20 juillet 2015, par Aryan Naim

  I’m trying to convert group of ".jpg" files acting as individual frames into 1 single mpeg video ".mp4"

  Example parameters i used :

  frame duration =2 secs

  frame rate =30 fps

  encoder = libx264 (mpeg)

  input pattern = "*.jpg"

  output pattern = video.mp4

  Based on ffmpeg wiki instructions at (https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20from%20images), I issued this command :

  ffmpeg -framerate 1/2 -pattern_type glob -i "*.jpg" -c:v libx264 -r 30 -pix_fmt yuv420p video.mp4

  Im getting this error :

  [image2 @ 049ab120] Pattern type ’glob’ was selected but globbing is not support
  ed by this libavformat build
  *.jpg : Function not implemented

  Which probably means the API pattern matching commands for my build/version have changed. By the way this my windows 32bit ffmpeg download build # ffmpeg-20150702-git-03b2b40-win32-static.

  How can I choose a group of files using pattern matching using ffmpeg ?

  Thanks