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• Preserving original colour spaces with FFmpeg

  12 décembre 2022, par Hashim Aziz

  I'm trying to implement some logic in my FFmpeg scripts to make sure that a video's colourspace is always preserved when upscaling. Just setting the metadata seems to be enough to do this, but the hard part is figuring out which metadata is needed, especially when the colourspace and related colour data reads as unknown, as is so often the case with many of my source videos.

  


  As I understand it, two things determine a video's original colourspace : whether a video is standard or high definition, and if it's standard definition, whether it's NTSC or PAL/SECAM. Based on this, I came up with the following logic to check the height of a video and set colourspace according to it :

  


  height=$(ffprobe -v error -select_streams v:0 -show_entries stream=width -of default=nw=1:nk=1 "$1" | tr -d $'\r')
colour_space=$(ffprobe -v error -select_streams v:0 -show_entries stream=color_space -of default=nw=1:nk=1 "$1" | tr -d $'\r')

# If input is standard definition and colourspace is BT601 (NTSC)
if [[ $height -lt 720 && $colour_space == "smpte170m" ]]; then 
colour_metadata="-colorspace smpte170m -color_trc smpte170m -color_primaries smpte170m" # set metadata to BT601 (NTSC)
# If input is standard definition and colourspace is BT601 (PAL and SECAM) or unknown
elif [[ $height -lt 720 && ($colour_space == "bt470bg" || $colour_space == "unknown") ]]; then 
colour_metadata="-colorspace bt470bg -color_trc gamma28 -color_primaries bt470bg" # set metadata to superior/more common PAL/SECAM
elif [[ $height -ge 720 ]]; then # If input is high definition
colour_metadata="-colorspace bt709 -color_trc bt709 -color_primaries bt709" # set metadata to BT.709
else echo "Unrecognised colorspace $color_space detected, leaving colour untouched"
fi


  


  Is this approach likely to work for the majority of videos ? Is there anything wrong with it that can be improved, or is it completely flawed for some reason that I'm missing ?

  


• FFMPEG : How to extract a PNG sequence from a video, remove duplicate frames in the process and keep the original frame number ?

  16 mai 2020, par Simon

  I have a recording of an old game which has variable framerate. Since I want to process individual frames to upscale and modernize the footage I would like to avoid any duplicate frames. I know that I can use this function to extract all frames from a video :

  



  ffmpeg -i input.mov -r 60/1 out%04d.png


  



  And I know that I can remove duplicate frames using this function :

  



  ffmpeg -i input.mov -vf mpdecimate,setpts=N/FRAME_RATE/TB output.mov


  



  However, the above command removes duplicate frames and puts frames next to each other whereas in order to keep a timecode of sorts it would be a lot more useful to be able to extract PNGs with frame number (video is progressive 60fps) but without all of the duplicates.

  



  So, the question is : what if I want to extract PNG files BUT maintain the original corresponding framenumber within the sequence ? So, if we have a video with 10 frames and frames 2-8 are duplicates it spits out 1.png 2.png 9.png and 10.png ? How do I combine both bits of code listed above ?

  


• avformat/movenc : added ability to use original stream ids as track ids instead of...

  31 août 2016, par Erkki Seppälä

  avformat/movenc : added ability to use original stream ids as track ids instead of regenerating them
  Sometimes it’s useful to be able to define the exact track numbers in
  
  the generated track, instead of always beginning at track id 1. Using
  
  the option use_stream_ids_as_track_ids now copies the use stream ids
  
  to track ids. Dynamically generated tracks (ie. tmcd) have their track
  
  numbers defined as continuing from the highest numbered stream id.
  Signed-off-by : Erkki Seppälä <erkki.seppala.ext@nokia.com>
  
  Signed-off-by : OZOPlayer <OZOPL@nokia.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

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