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• ffmpeg : convert video1->images->video2 produce different number of seconds in video1,video2

  25 mai 2016, par mrgloom

  I’m trying to convert video to images, make some image processing and then convert images back to video.

  Code :

  VIDEO_PATH="/home/user/myvideo.mp4"
  
  SEPARATOR='/'
  
  BITRATE="4600k"
  
  
  
  VIDEO_BASE_DIR=`dirname $VIDEO_PATH`
  
  FRAMES_DIR=$VIDEO_BASE_DIR$SEPARATOR"Frames"
  
  mkdir $FRAMES_DIR
  
  
  
  #check info of original video
  
  ./ffprobe -show_streams $VIDEO_PATH
  
  
  
  #video to images
  
  ./ffmpeg -i $VIDEO_PATH $FRAMES_DIR$SEPARATOR"image%d.png"
  
  
  
  #images to video
  
  ./ffmpeg -y -pattern_type glob -i $FRAMES_DIR$SEPARATOR'*.png' -r 30 -vcodec mpeg4 -b:v $BITRATE $VIDEO_BASE_DIR$SEPARATOR$BITRATE.mp4
  
  
  
  #check info of produced video
  
  ./ffprobe -show_streams $VIDEO_BASE_DIR$SEPARATOR$BITRATE.mp4

  The problem is that length in second of original and produced videos doesn’t match.

  In ffprobe output I can see that r_frame_rate=30/1 for both videos.
  And nb_frames don’t match nb_frames=339 for first and nb_frames=407 for second video.

  UPDATE :

  Seems this command with -framerate solved the problem :

  ./ffmpeg -framerate 30 -y -start_number 1 -i $FRAMES_DIR$SEPARATOR"image%d.png" -r 30 -vcodec h264 -b:v $BITRATE $VIDEO_BASE_DIR$SEPARATOR$BITRATE.mp4

• How to compare audio channel differences with FFmpeg ?

  30 septembre 2021, par Deivedux

  I'm making a little script for myself to quickly go through a large volume of video and audio files to compress audio for extra space, but for extra efficiency, I also don't want to waste space by keeping both channels if they're identical.

  


  My issue is that I don't know how to, let's say, check if their decoded versions are at least a 99.99% match, in which case I'd only encode the left channel into mono.

  


  How would I go about doing this ?

  


• movenc : Add a flag for indicating a discontinuous fragment

  20 novembre 2014, par Martin Storsjö

  movenc : Add a flag for indicating a discontinuous fragment
  This allows creating a later mp4 fragment without sequentially
  
  writing the earlier ones before (when called from a segmenter).
  Normally when writing a fragmented mp4 file sequentially, the
  
  first timestamps of a fragment are adjusted to match the
  
  end of the previous fragment, to make sure the timestamp is the
  
  same, even if it is calculated as the sum of previous fragment
  
  durations. (And for the first packet in a file, the offset of
  
  the first packet is written using an edit list.)
  When writing an individual mp4 fragment discontinuously like this
  
  (with potentially writing the earlier fragments separately later),
  
  there’s a risk of getting a gap in the timeline if the duration
  
  field of the last packet in the previous fragment doesn’t match up
  
  with the start time of the next fragment.
  Using this requires setting -avoid_negative_ts make_non_negative
  
  (or -avoid_negative_ts 0).
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/movenc.c
  • [DH] libavformat/movenc.h