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• Is ffmpeg's chromakey filter broken when matching black/white ?

  7 janvier 2023, par Taylor Brown

  I have a file, colors.png. It looks like this :

  



  Let's say I want to make the red square transparent. When I run ffmpeg -i colors.png -filter_complex "[0]chromakey=0xff0000:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-red.png (notice I use similarity=0.1 to make this work), I get exactly that :

  



  How about making the blue square transparent ? ffmpeg -i colors.png -filter_complex "[0]chromakey=0x0000ff:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-blue.png works too !

  



  But what about replacing black ? ffmpeg -i colors.png -filter_complex "[0]chromakey=0x000000:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-black.png gives me this :

  



  And likewise, replacing white with ffmpeg -i colors.png -filter_complex "[0]chromakey=0xffffff:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-white.png gives me the same result :

  



  Why is this ? Even if I use similarity=0.01, which according to the docs "matches only the exact key color", this still doesn't work when I'm trying to make black/white transparent. Is ffmpeg broken, or am I misunderstanding the chromakey filter ?

  


• How to remove black bars with ffmpeg ?

  3 novembre 2022, par watch-this

  I'm trying to remove black bars from a 637×478 video

  


  

  


  here's what happens :

  


  % ffmpeg -i sfu11.mp4 -vf "scale=ih*16/9:ih,scale=iw:-2,setsar=1" -y out.mp4 
ffmpeg version 5.1.2 Copyright (c) 2000-2022 the FFmpeg developers
  built with Apple clang version 14.0.0 (clang-1400.0.29.102)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  libavdevice    59.  7.100 / 59.  7.100
  libavfilter     8. 44.100 /  8. 44.100
  libswscale      6.  7.100 /  6.  7.100
  libswresample   4.  7.100 /  4.  7.100
  libpostproc    56.  6.100 / 56.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'sfu11.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf57.83.100
  Duration: 01:02:49.37, start: 0.000000, bitrate: 15 kb/s
  Chapters:
    Chapter #0:0: start 0.000000, end 99.833000
      Metadata:
        title           : Chapter 01
    Chapter #0:1: start 99.833000, end 701.818000
      Metadata:
        title           : Chapter 02
    Chapter #0:2: start 701.818000, end 1213.746000
      Metadata:
        title           : Chapter 03
    Chapter #0:3: start 1213.746000, end 1726.892000
      Metadata:
        title           : Chapter 04
    Chapter #0:4: start 1726.892000, end 2167.882000
      Metadata:
        title           : Chapter 05
    Chapter #0:5: start 2167.882000, end 2816.430000
      Metadata:
        title           : Chapter 06
    Chapter #0:6: start 2816.430000, end 3769.366000
      Metadata:
        title           : Chapter 07
  Stream #0:0[0x1](und): Video: hevc (Main 10) (hvc1 / 0x31637668), yuv420p10le(tv, progressive), 708x478 [SAR 9:10 DAR 1593:1195], 544 kb/s, 23.98 fps, 23.98 tbr, 24k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 341 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Data: bin_data (text / 0x74786574)
    Metadata:
      handler_name    : SubtitleHandler
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x7f8630806e00] width not divisible by 2 (849x478)
Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
[aac @ 0x7f8630809d00] Qavg: 15927.165
[aac @ 0x7f8630809d00] 2 frames left in the queue on closing
Conversion failed!


  


  However, the same flags work using ffplay but I get horizontal black bars instead.

  


  % ffplay -i sfu11.mp4 -vf "scale=ih\*16/9:ih,scale=iw:-2,setsar=1"


  


  

  


  I also tried using the cropdetect filter. It doesn't work and end up with the very same black bars while passing -vf crop=....

  


• FFMPEG segment creates black frame in the beginning - and key_frame looks offset [closed]

  30 septembre 2022, par jackyroo

  I'm trying to split a video using ffmpeg segment :

  


  ffmpeg -r 60 -accurate_seek -I input.mov -map 0:a? -map 0:v? -codec copy -reset_timestamps 1 -map_metadata 0 -avoid_negative_ts 1 -f segment output_%%03d.mov -y -loglevel debug

  


  The problem with this approach is that the first split segment has 2 black frames at the beginning, while the consecutive ones are fine.

  


  I cannot figure out why, and I'm genuinely lost in this process.

  


  I've also tried specifying -force_key_frames but it makes no difference at all.

  


  Then I found something interesting by comparing keyframes of the original video and the first split chunk using this command :

  


  ffprobe -select_streams v -skip_frame nokey -show_frames -v quiet input.mov

  


  Original Video KeyFrames
The first keyframe of the original video looks fine :

  


  [FRAME]
media_type=video
stream_index=0
key_frame=1
pts=0
pts_time=0.000000
pkt_dts=127488
pkt_dts_time=8.300000
best_effort_timestamp=0
best_effort_timestamp_time=0.000000
pkt_duration=256
pkt_duration_time=0.016667
duration=256
duration_time=0.016667
pkt_pos=40
pkt_size=128838
width=1420
height=2000
pix_fmt=yuv420p
sample_aspect_ratio=N/A
pict_type=I
coded_picture_number=0
display_picture_number=0
interlaced_frame=0
top_field_first=0
repeat_pict=0
color_range=unknown
color_space=unknown
color_primaries=unknown
color_transfer=unknown
chroma_location=left
[SIDE_DATA]
side_data_type=H.26[45] User Data Unregistered SEI message
[/SIDE_DATA]
[/FRAME]


  


  Split Video - First Chunk Keyframes

  


  On the other hand, it seems like the first keyframe of the chunk (the one with the two added black frames in the beginning) gets shifted !

  


  [FRAME]
media_type=video
stream_index=1
key_frame=1
pts=507
pts_time=0.033008
pkt_dts=N/A
pkt_dts_time=N/A
best_effort_timestamp=507
best_effort_timestamp_time=0.033008
pkt_duration=256
pkt_duration_time=0.016667
duration=256
duration_time=0.016667
pkt_pos=40
pkt_size=128838
width=1420
height=2000
pix_fmt=yuv420p
sample_aspect_ratio=N/A
pict_type=I
coded_picture_number=0
display_picture_number=0
interlaced_frame=0
top_field_first=0
repeat_pict=0
color_range=unknown
color_space=unknown
color_primaries=unknown
color_transfer=unknown
chroma_location=left
[SIDE_DATA]
side_data_type=H.26[45] User Data Unregistered SEI message
[/SIDE_DATA]
[/FRAME]


  


  Might this be the cause of the two black frames at the beginning ?

  


  The following is the first (and only) keyframe of the second chunk, and it looks fine :

  


  [FRAME]
media_type=video
stream_index=1
key_frame=1
pts=0
pts_time=0.000000
pkt_dts=N/A
pkt_dts_time=N/A
best_effort_timestamp=0
best_effort_timestamp_time=0.000000
pkt_duration=256
pkt_duration_time=0.016667
duration=256
duration_time=0.016667
pkt_pos=40
pkt_size=158598
width=1420
height=2000
pix_fmt=yuv420p
sample_aspect_ratio=N/A
pict_type=I
coded_picture_number=0
display_picture_number=0
interlaced_frame=0
top_field_first=0
repeat_pict=0
color_range=unknown
color_space=unknown
color_primaries=unknown
color_transfer=unknown
chroma_location=left
[/FRAME]


  


  Please help me spreading some light over this...

  


  Thanks !