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• Combining 2 FFMPEG Commands

  11 juillet 2020, par John Doe

  I'm trying to combine 2 ffmpeg commands, one which creates the video, and another which adds a simple fade to the beginning of the created video. Here's what I have :

  


  ffmpeg -y -stream_loop -1 -i "video.mp4" -stream_loop -1 -i "music.mp3" -i "audio.mp3" -filter_complex "[1:a]volume=0.1[a1];[2:a]adelay=5000|5000,apad=pad_dur=10[a2];[a1][a2]amerge=inputs=2,afade=in:st=0:d=5[audio]" -map "0:v" -map "[audio]" -c:v libx264 -c:a aac -ac 2 -ar 22050 -preset veryfast -shortest "output.mp4"

ffmpeg -y -i "output.mp4" -filter_complex "[0:v]fade=in:0:d=5" -c:a copy -preset veryfast -movflags faststart -fflags genpts "done.mp4"


  


  The two commands work perfectly fine, however the second one takes about the same amount of time to process as the first, and I feel it should be relatively easy to do the fade-in during the first encode. For my skillset atleast, I was wrong. Please could someone with more experience lend a helping hand ?

  


  Thanks.

  


• faster way to downmix 5.1 videos to stereo ?

  22 octobre 2020, par alex hansen

  I have a hand full of movies that are all in 5.1 audio, i need there to be one audio track that is only in stereo. i have found a few suggestions as to how to do this but some dont work for me and others are way too slow.

  


  the one i found that works the fastest is this :

  


  ffmpeg -y -i "input" -map 0:v -c:v copy -map 0:a:0? -c:a:0 copy -map 0:a:0? -c:a:1 aac -ac 2 -metadata:s:a:1 title="Eng 2.0 Stereo" -map 0:a:1? -c:a:2 copy -map 0:a:2? -c:a:3 copy -map 0:a:3? -c:a:4 copy -map 0:a:4? -c:a:5 copy -map 0:a:5? -c:a:6 copy -map 0:a:6? -c:a:7 copy -map 0:s? -c:s copy "output"   


  


  sadly i do not remember where it came from.

  


  the problem with this being that it creates a separate audio track, and for my purposes this does not work.

  


  doing just the standard -ac 2 works but is way to slow, i estimated to take over 40 hours to go through all my movies.

  


  edit :
a bit of extra information to throw in here

  


  

  • all the movies are mp4's

  


  • all except 2 movies are 5.1 audio (there is 1 7.1 and 1 mono. i dont really care about them tho)

  


  • the command i posted runs at about a 40x speed while just doing -ac 4 runs at 2x speed

  


  


• Read, process and save video and audio with FFMPEG

  3 mai 2017, par sysseon

  I want to open a video resource with ffmpeg on Python, get the read frames from the pipe, modify them (e.g. put the timestamp with OpenCV) and write the result to an output video file. I also want to save the audio source with no changes.

  My code (with no audio and two processes) :

  import subprocess as sp
  
  import numpy as np
  
  # import time
  
  # import cv2
  
  
  
  FFMPEG_BIN = "C:/ffmpeg/bin/ffmpeg.exe"
  
  INPUT_VID = 'input.avi'
  
  res = [320, 240]
  
  
  
  command_in = [FFMPEG_BIN,
  
                '-y',  # (optional) overwrite output file if it exists
  
                '-i', INPUT_VID,
  
                '-f', 'image2pipe',  # image2pipe or rawvideo?
  
                '-pix_fmt', 'bgr24',
  
                '-vcodec', 'rawvideo',
  
                '-']
  
  
  
  command_out = [FFMPEG_BIN,
  
                 '-y',  # (optional) overwrite output file if it exists
  
                 '-f', 'rawvideo',
  
                 '-vcodec', 'rawvideo',
  
                 '-s', '320x240',
  
                 '-pix_fmt', 'bgr24',
  
                 '-r', '25',
  
                 '-i', '-',
  
                 # '-i', INPUT_VID,    # Audio
  
                 '-vcodec', 'mpeg4',
  
                 'output.mp4']
  
  
  
  pipe_in = sp.Popen(command_in, stdout=sp.PIPE, stderr=sp.PIPE)
  
  pipe_out = sp.Popen(command_out, stdin=sp.PIPE, stderr=sp.PIPE)
  
  
  
  while True:
  
      # Read 320*240*3 bytes (= 1 frame)
  
      raw_image = pipe_in.stdout.read(res[0] * res[1] * 3)
  
      # Transform the byte read into a numpy array
  
      image = np.fromstring(raw_image, dtype=np.uint8)
  
      image = image.reshape((res[1], res[0], 3))
  
      # Draw some text in the image
  
      # draw_text(image)
  
  
  
      # Show the image with OpenCV (not working, gray image, why?)
  
      # cv2.imshow("VIDEO", image)
  
  
  
      # Write image to output process
  
      pipe_out.stdin.write(image.tostring())
  
  
  
  print 'done'
  
  pipe_in.kill()
  
  pipe_out.kill()

  1. Could it be done with just a process ? (Read the input from a file,
     put it in the input pipe, get the image, process it, and put it in
     the output pipe to be saved into a video file)
  2. How can I save the audio ? In this example, I could use ’-i
     INPUT_VID’ in the second process to get the audio channel, but my
     source will be a RTSP, and I don’t want to create a connection for
     each process. Could I put video+audio in the pipe and rescue and
     separate it with numpy ? How ?
  3. I use a loop to process the frames and wait until I get an error.
     How can I check if all frames are already read ?
  4. Not important, but if I try to show the images with OpenCV
     (cv2.imshow(...)), I only see a gray screen. Why ?