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• ffmpeg concatenating videos of different fps while keeping the total length not changed

  23 novembre 2017, par A_Matar

  I wanna pad an mp4 video stream with another video clip of a static image that I created using :

  def generate_white_vid (duration):
  
      output_filename = os.path.join(p_path,'white_vid_'+" 0:.2f}".format(duration)+'.mp4')
  
      ffmpeg_create_vid_from_static_img = 'ffmpeg -loop 1 -i /path/WhiteBackground.jpg -c:v libx264 -t %f -pix_fmt yuv420p -vf scale=1920:1080 %s' % (duration, output_filename)
  
      p = subprocess.Popen(ffmpeg_create_vid_from_static_img, shell=True)
  
      p.communicate()
  
      return output_filename

  I use the following to concatenate :

  def concat_vids(clip_paths):
  
      filenames_txt = open('clips_to_join.txt','w')
  
      for clip in clip_paths:
  
          filenames_txt.write ('file \''+ clip+'\'\n')
  
      filenames_txt.close()
  
      output_filename = clip_paths[0].split('.', 2)[0]
  
      output_file_path = os.path.join(root_path, output_filename+'-padded.mp4')
  
      # join the clips
  
      ffmpeg_command = ["ffmpeg", "-f", "concat", "-safe", "0", "-i", "clips_to_join.txt", "-codec", "copy", output_file_path] # output_filename = ch0X-start_time-end_time
  
      p = subprocess.Popen(ffmpeg_command)
  
      p.communicate() # wait till the subprocess finishes. You can send commands to process as well.
  
      return output_file_path

  When I check the length of the resulting video after concatenation, I find that it is not equal to the sum of the two segments that I concatenated, and sometimes it is even less by some seconds !!

  Here is how I get the video length in seconds :

  def ffmpeg_len(vid_path):
  
      '''
  
      Returns length in seconds using ffmpeg
  
      '''
  
      ffmpeg_get_mediafile_length = ['sh', '-c', 'ffmpeg -i "$1" 2>&1 | grep Duration', '_', vid_path]
  
      p = subprocess.Popen(ffmpeg_get_mediafile_length, stdout=subprocess.PIPE, stderr=subprocess.PIPE)    
  
      output, err = p.communicate()
  
      length_regexp = 'Duration: (\d{2}):(\d{2}):(\d{2})(\.\d+),'
  
      re_length = re.compile(length_regexp)
  
      matches = re_length.search(output)
  
      if matches:
  
          video_length = int(matches.group(1)) * 3600 + \
  
                          int(matches.group(2)) * 60 + \
  
                          int(matches.group(3)) + float(matches.group(4))
  
          return video_length
  
      else:
  
          print("Can't determine video length.")
  
          print err
  
          raise SystemExit

  My guess is that maybe the concatenation unifies the fps rate for the all the clips to be joined, if this is the case, how to prevent this from happening ? How can I get a video of the desired length exactly.

  Maybe it worth mentioning that the video to padded is very short 0.42 second, the original video is 210.58 and the resultant video is 210.56 !

  I have verified that ffmpeg does generate the desired padding region and it is of the desired length 0.42 I got a 0.43 segment when I forced 30 fps but it is okay.

• ffmpeg - how can I scale the video while perserving the total frames in it ?

  14 juin 2018, par choz

  I have a video with a size of 515 x 755, that I would like to resize proportionally to 206 x 302 (so, factor is 2.5).

  In this video, I have the total of 588 frames, and I use ffmpeg to scale it, with this command.

  ffmpeg -i video.mp4 -vf scale=206:-1 xRotation_206.mp4

  And I use this to check how many frames are there in the video, based on this answer.

  ffmpeg -i video.mp4 -map 0:v:0 -c copy -f null - 2>&1 | awk '/frame=/ {print $2}'

  The original video frames is good (588 frames). But, after resizing with the command above, my converted video now has 604 frames.

  The question is, how can I resize the video by preserving the total frames in it ? It doesn’t really have to be ffmpeg approach, and any suggestion is appreciated.

  Here’s the sample video that I use : Link

• How do I set total file duration generating a piped mp4 with ffmpeg ?

  9 avril 2021, par Mikhail Novikov

  My task is to generate (by piping, so that a file can be played at the same time with generation) an mp4 file which is a part of a larger file, with the result looking like a static file link, being seekable before it fully loads (i.e. supporting range headers).

  


  Here is how I do it now :

  


  ffmpeg -ss $1 -i teststream_hls1_replay.mp4 -t $2 -timecode $3 \
       -codec copy -movflags frag_keyframe+faststart -f mp4 pipe:1


  


  Result is OK (video starts from the right point) except the player does not see the total duration of a file so a controlbar looks weird, and seeking isn't possible properly, just because the controlbar jumps all the time.

  


  How do I indicate to ffmpeg that it has to set moov atom to contain right duration ?

  


  Basically the question boils down to : how do I force set some arbitrary duration of file in a moov atom, when I am generating a fragmented mp4 ? ffmpeg will not get know how long will it be, so explainably it can't do it itself, but I know... is there a command line parameters to specify a 'forced duration' ?