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• How to print AVFrame->pts in the 00:00:00.033 format ?

  16 janvier 2018, par siods333333

  I need to convert AVFrame->pts into the "00:00:00.033" formatted string, how should I do this ? It is in the AVStream->time_base scale, instead of the ffmpeg standard 1,000,000 scale, need to convert that too.

  I need to walk+decode the entire file, just to get keyframes and duration. Will pass them to ffmpeg filters after that.

  Should the first keyframe have timecode "00:00:00.000" or "00:00:00.033" ? Avidemux uses the latter, don’t know about the ffmpeg.

  I want to know if duration should be the pts of the last frame, or pts of the last frame plus one ?

• In ffmpeg, how to search to a keyframe BEFORE a specified time ?

  12 janvier 2018, par siods333333

  Background

  For a video in the mp4 or flv container formats, I need to :

  1. Get its duration.

  2. Get a keyframe at 25% of its duration. If frame at 25% isn’t a keyframe, seek to the first keyframe before that frame.

  3. Seek to audio at 10ms before that keyframe.

  According to the following comment on StackOverflow, av_seek_frame seems to only seek to a keyframe after a specified time.

  Question

  Given that it appears I can only seek after a specified time, how is it possible to get the required keyframe and to seek to the correct part in a mp4 or flv container as specified above ?

  My Ideas

  • My best bet is probably parsing the header (and index, where applicable) manually, and then use the av_seek_frame with the AVSEEK_FLAG_BYTE flag.

  • Or I can just walk the whole file, and just check if AVFrame->key_frame is true or not.

  It would be awesome if the trim filter could support different seek methods, but I guess I have to get correct timestamps by myself, is that correct ?

• Issue opening video file with OpenCV VideoCapture

  6 décembre 2017, par user1938805

  I’ve been reviewing the multitudes of similar questions for this issue, but I’m afraid I just cannot figure out why I cannot open a file in opencv

  I have a file "small.avi", which is a reencoding of "small.mp4" that I got from the internet. I reencoded it with ffmpeg -i small.mp4 small.avi, and I did this because I couldn’t open a mp4 file either and online it recommended trying an avi format first.

  Here is my code (mostly copied from a tutorial, with a few lines to show some relevant info) :

  import cv2
  
  import os
  
  
  
  for _, __, files in os.walk("."):
  
      for file in files:
  
          print file
  
  print ""
  
  
  
  cap = cv2.VideoCapture("small.mp4")
  
  print cap.isOpened()
  
  print cap.open("small.avi")
  
  i = 0
  
  while cap.isOpened() and i < 10:
  
      i += 1
  
      ret, frame = cap.read()
  
      print "read a frame"
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
      cv2.imshow('frame', gray)
  
      if cv2.waitKey(1) & 0xFF == ord('q'):
  
          break
  
  cap.release()
  
  cv2.destroyAllWindows()

  This produces the following output :

  "A:\Program Files\AnacondaPY\Anaconda\python.exe" A:/Documents/Final/VideoProcessor.py
  
  small.avi
  
  small.mp4
  
  VideoProcessor.py
  
  
  
  False
  
  False
  
  
  
  Process finished with exit code 0

  My program does not appear to properly open either file. Following the advice of

  Can not Read or Play a Video in OpenCV+Python using VideoCapture

  and

  Cannot open ".mp4" video files using OpenCV 2.4.3, Python 2.7 in Windows 7 machine,

  I found my cv2 version to be 3.0.0, went to

  A :\Downloads\opencv\build\x86\vc12\bin

  and copied the file opencv_ffmpeg300.dll to

  A :\Program Files\AnacondaPY\Anaconda

  Despite this, the code still does not successfully open the video file. I even tried the x64 versions, and tried naming the file opencv_ffmpeg.dll, opencv_ffmpeg300.dll, and opencv_ffmpeg300_64.dll (for the x64 version). Is there anything else I can try to fix this ?

  Thanks for any help