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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 with mp4 file, segment and concatenate doesn't recreate the original video, why ?

  5 février 2023, par tttterrgi79

  I'm trying to segment and concatenate mp4 file with FFmpeg.

  


  First I segment the video file :

  


  ffmpeg -i input.mp4 -c copy -map 0 -f segment -reset_timestamps 1 output%03d.mp4


  


  Then I concatenate

  


  ffmpeg -f concat -safe 0 -i list.txt -c copy -movflags faststart done.mp4 


  


  My expectation is that the videos should be the exact same, however a lot of differences appear, the bytes size is slightly different, then with FFprobe I find differences in streams, as both video streams and audio streams have different starting times and durations.

  


  The reason I'm asking this, because I want to first segment the file, then reencode several parts of the video with different program, and then concatenate back, but this will not work if timestamps are messed up in the process.

  


• Playing 120fps in browser between original and re-made video, original is normal speed, new video is slo-mo

  1er mars 2023, par Patrick Vellia

  I used my GoPro Hero10 to record at 4k 120fps on a green screen. This original video plays slo-mo in QuickTime but "normal" speed in the browser. I want it playing normal speed, and if end user wants to slow it down they have the extra frames for that to maintain clarity, which is why I record at 120.

  


  I then used FFMPEG to create an image sequence of the video.

  


  Then I ran Image Magic to create the transparent frames.

  


  Then I put it back together with the following command for a HEVC mov file :

  


  ffmpeg -r 120 -f image2 -i transparent/image_transparent_%08d.png -vcodec hevc_videotoolbox -crf 28 -alpha_quality 1  -tag:v hvc1 output.mov


  


  I am still on an Intel MacBook Pro running FFMPEG 4.6 (as I've found 5+ was buggy with one of my commands a few months ago but can't remember which one, I think it was the videotoolbox).

  


  The GoPro video has the following stream data as input to the FFMPEG :

  


  Duration: 00:00:08.15, start: 0.000000, bitrate: 60160 kb/s
  Stream #0:0(eng): Video: hevc (Main) (hvc1 / 0x31637668), yuvj420p(pc, bt709), 3840x2160 [SAR 1:1 DAR 16:9], 59891 kb/s, 119.88 fps, 119.88 tbr, 120k tbn, 119.88 tbc (default)
    Metadata:
      creation_time   : 2023-02-28T19:06:41.000000Z
      handler_name    : GoPro H.265
      vendor_id       : [0][0][0][0]
      encoder         : GoPro H.265 encoder
      timecode        : 19:05:32:105
  Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)
    Metadata:
      creation_time   : 2023-02-28T19:06:41.000000Z
      handler_name    : GoPro AAC  
      vendor_id       : [0][0][0][0]
      timecode        : 19:05:32:105
  Stream #0:2(eng): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
    Metadata:
      creation_time   : 2023-02-28T19:06:41.000000Z
      handler_name    : GoPro TCD  
      timecode        : 19:05:32:105
  Stream #0:3(eng): Data: bin_data (gpmd / 0x646D7067), 76 kb/s (default)
    Metadata:
      creation_time   : 2023-02-28T19:06:41.000000Z
      handler_name    : GoPro MET  


  


  Whereas the re-constructed video has the following data :

  


  Duration: 00:00:08.13, start: 0.000000, bitrate: 763650 kb/s
  Stream #0:0: Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, progressive), 3840x2160 [SAR 1:1 DAR 16:9], 763696 kb/s, 120 fps, 120 tbr, 15360 tbn, 15360 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : FFMP
      encoder         : Lavc58.134.100 hevc_videotoolbo


  


  When this re-constructed video plays in the browser, it is in slow-mo and I need to set the playbackRate to 4.0 for it to play "normally".

  


  Is there something I need to add to the video for the browser to play it at "normal" speed ?