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• The duration of movie file recorded by AVAssetWriter is not correct

  1er mars 2016, par ideawu

  I am recording video files with AVAssetWriter combining with AVCaptureVideoDataOutputSampleBufferDelegate. So I can take control over every frame the camara gives in the method :

  - (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
  
      double time = CMTimeGetSeconds(CMSampleBufferGetPresentationTimeStamp(sampleBuffer));
  
      NSLog(@"%f", time);
  
      [_videoInput appendSampleBuffer:sampleBuffer];
  
  }

  So I am so sure how many samples have been written to AVAssetWriter via AVAssetWriterInput, and I know exactly the start time and end time of the samples being written. The duration is calculated by end_time - start_time. Say the duration calculated in the video capture programm is 0.5 second.

  I get the .mov/.mp4 file on disk, inspected with ffmpeg -i, it shows a very different duration.

  ffmpeg -i m003.mp4 2>&1 | grep Dura
  
    Duration: 00:00:01.37, start: 0.836667, bitrate: 95 kb/s

  The movie file show a duration of 1.37 seconds, which it’s quite different with the EXACT duration 0.5.

  Does any one knows the reason ?

• Movie from PNGs using FFmpeg and Python - rgb24 vs yuv420p

  7 février 2016, par Eilam G

  I wrote a little Python program to grab a bunch of PNGs and render them into a movie using the FFmpeg command line. The PNGs are read into [X*Y*3] numpy arrays (ignoring the alpha channel), new frames are added via interpolation, and the data is fed into FFmpeg as a pipe and saved as an mp4.

  The files play fine in VLC on Windows, but don’t work in iMovie on a Mac. I think it might have to do with most programs expecting H264 videos to be in the YUV420P color space, which my movies aren’t. I’ve tried changing the ffmpeg command -pix_fmt from rgb24 to yuv420p, but no go.

  Relevant Python code attached below.

  def init_vars(args):
  
      global log_file, file_names, command, num_int_frames, num_files, silent
  
  
  
      file_names = glob('./*.png')
  
      num_files = len(file_names)
  
  
  
      if args.log:
  
          log_file = 'bmmp.log'
  
      else:
  
          log_file = os.devnull
  
  
  
      silent = args.silent
  
  
  
      frames_per_second = args.fps
  
      wanted_movie_length = args.length
  
      movie_file_name = args.name + '.mp4'
  
  
  
      num_int_frames = round((frames_per_second * wanted_movie_length - 1) / (num_files - 1) - 1)
  
  
  
      if sys.platform == 'win32':
  
          ffmpeg_bin = 'ffmpeg.exe'
  
      else:
  
          ffmpeg_bin = 'ffmpeg'
  
  
  
      command = [ffmpeg_bin,
  
                 '-y', # (optional) overwrite output file if it exists
  
                 '-f', 'rawvideo',
  
                 '-vcodec','rawvideo',
  
                 '-s', '1280x720', # size of one frame
  
                 '-pix_fmt', 'rgb24',
  
                 '-r', str(frames_per_second), # frames per second
  
                 '-i', '-', # The input comes from a pipe
  
                 '-an', # Tells FFMPEG not to expect any audio
  
                 movie_file_name]

  Cheers,
  Eilam

• Convert TIFF images sequence to lossless movie FFMPEG

  9 janvier 2016, par Rarez

  I would like use a h265 codec(FPS must be equal to 25) to save loseless wideo from sequence of TIFF images. I have a problem with save it. I supose that it is little mistake. I tried many combinactions of commands here is last one :

  ffmpeg -f image2 -r $FRAMERATE -i IMG_%03d.tif -vcodec libx265 -x265-params lossless movie.mp4

  And output :

  [libx265 @ 0x2bcaf40] 4:2:2 and 4:4:4 support is not fully defined for HEVC yet. Set -strict experimental to encode anyway.
  
  Output #0, mp4, to 'movie.mp4':
  
      Stream #0:0: Video: hevc, none, q=2-31, 128 kb/s, SAR 1:1 DAR 0:0, 25 fps
  
      Metadata:
  
        encoder         : Lavc57.20.100 libx265
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (tiff (native) -> hevc (libx265))
  
  Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

  I will be very glad for any help. Thanks