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• ffmpeg converting PCM data file to wav file getting distorted(noisy) data

  3 janvier 2015, par Mahendra

  I have raw pcm data in following form :

  0000 0000 0000 0000 0000 0000 0000 0000
  
  0000 0000 0000 0000 0000 0000 0000 0000
  
  0000 0000 0000 0000 0000 0000 0000 0000
  
  0000 0000 0000 0000 0000 0000 0000 0100
  
  0000 0000 0000 0000 0000 0000 0000 0000
  
  0000 0100 0100 0000 0000 efbf bdef bfbd
  
  0000 efbf bdef bfbd efbf bdef bfbd efbf
  
  bdef bfbd efbf bdef bfbd efbf bdef bfbd
  
  efbf bdef bfbd efbf bdef bfbd 0000 efbf
  
  bdef bfbd 0000 efbf bdef bfbd efbf bdef
  
  bfbd 2900 efbf bdef bfbd 0000 efbf bdef
  
  bfbd efbf bdef bfbd efbf bdef bfbd 0000

  and I want to make this data in wav file when I am converting by ffmpeg getting noisy data by this command :

  sox -V -t raw -b 16 -e signed -r 16000 -c 1 14_32_7_187.pcm  new.wav

  and :

  ffmpeg -f s16le -ar 16000 -ac 1 -i 14_32_7_187.pcm -ar 16000 -ac 1 oout.wav

  using both getting noisy data.

• How to save frame from VOB with correct size ?

  18 mars 2017, par Paulo Barretto

  I am saving single frames from a vob file with ffmpeg.

  ffprobe shows for my vob file :

  Stream #0:1[0x1e0] : Video : mpeg2video (Main), yuv420p(tv), 720x480
  [SAR 8:9 DAR 4:3], Closed Captions, 3750 kb/s, 29.97 fps, 29.97 tbr,
  90k tbn, 59.94 tbc

  My command line is

  ffmpeg -i File1.vob -ss 10 -q:v 2 -vframes 1 -an -sn frame10s.jpg

  My jpeg files are being saved with 720x480, horizontally stretched. How can I make them be saved with correct display ratio 640x480 ?

• 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 ?