[FFmpeg-user] lagfun misunderstanding?

Sun Mar 29 16:07:59 EEST 2020

Hi Folks,
     I'm exploring the lagfun filter and think I may have some fundamental
misunderstanding as I'm not getting the results I expect.

I have a video of green lasers on glassware in the dark and wish to make the
laser flashes persist.
My attempts so far seem to result in the green flashes persisting as white,
however.

I tried this command which I think  should do this:
Take the YUV input video, split it into RGB, run lagfun on only the green
content, save resulting output.

ffmpeg -i IMG_1685.MOV -q:v 0 -vcodec h264 -acodec aac -strict -2 -filter:v
format=pix_fmts=rgb24,lagfun=decay=0.999 greenlagtest.mp4

Input file is here: http://www.robinbussell.co.uk/mov/IMG_1685.MOV  (far too
much camera movement, I know!) 
Output here: http://www.robinbussell.co.uk/mov/greenlagtest.mp4

Console output is:

ffmpeg version 4.2.2-1build1~18.04.sav0 Copyright (c) 2000-2019 the FFmpeg
developers
  built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
  configuration: --prefix=/usr --extra-version='1build1~18.04.sav0'
--toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu
--incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl
--disable-stripping --enable-avresample --disable-filter=resample
--enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom
--enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca
--enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig
--enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm
--enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg
--enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg
--enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr
--enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame
--enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack
--enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid
--enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal
--enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394
--enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r
--enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'IMG_1685.MOV':
  Metadata:
    major_brand     : qt
    minor_version   : 0
    compatible_brands: qt
    creation_time   : 2020-03-28T12:20:59.000000Z
  Duration: 00:00:18.53, start: 0.000000, bitrate: 3829 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv,
bt709), 1280x720, 3823 kb/s, 60.01 fps, 60 tbr, 600 tbn, 1200 tbc (default)
    Metadata:
      creation_time   : 2020-03-28T12:20:59.000000Z
      handler_name    : Core Media Video
      encoder         : H.264
    Stream #0:1(und): Data: none (mebx / 0x7862656D), 0 kb/s (default)
    Metadata:
      creation_time   : 2020-03-28T12:20:59.000000Z
      handler_name    : Core Media Metadata
    Stream #0:2(und): Data: none (mebx / 0x7862656D), 0 kb/s (default)
    Metadata:
      creation_time   : 2020-03-28T12:20:59.000000Z
      handler_name    : Core Media Metadata
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x55a16881aec0] using cpu capabilities: MMX2 SSE2Fast SSSE3
SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x55a16881aec0] profile High 4:4:4 Predictive, level 3.2, 4:4:4
8-bit
[libx264 @ 0x55a16881aec0] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC
codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options:
cabac=1 ref=3 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1
psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=0
cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=12
lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0
bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0
direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40
intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0
qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'greenlagtest.mp4':
  Metadata:
    major_brand     : qt
    minor_version   : 0
    compatible_brands: qt
    encoder         : Lavf58.29.100
    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv444p,
1280x720, q=-1--1, 60 fps, 15360 tbn, 60 tbc (default)
    Metadata:
      creation_time   : 2020-03-28T12:20:59.000000Z
      handler_name    : Core Media Video
      encoder         : Lavc58.54.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
frame= 1112 fps= 50 q=-1.0 Lsize=    6912kB time=00:00:18.48
bitrate=3063.4kbits/s speed=0.833x
video:6905kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 0.101704%
[libx264 @ 0x55a16881aec0] frame I:5     Avg QP:22.29  size: 50576
[libx264 @ 0x55a16881aec0] frame P:968   Avg QP:25.09  size:  6873
[libx264 @ 0x55a16881aec0] frame B:139   Avg QP:24.68  size:  1178
[libx264 @ 0x55a16881aec0] consecutive B-frames: 81.5%  4.1%  4.3% 10.1%
[libx264 @ 0x55a16881aec0] mb I  I16..4: 54.6%  0.0% 45.4%
[libx264 @ 0x55a16881aec0] mb P  I16..4:  4.5%  0.0%  0.7%  P16..4: 36.1% 
6.4%  5.3%  0.0%  0.0%    skip:46.9%
[libx264 @ 0x55a16881aec0] mb B  I16..4:  0.6%  0.0%  0.0%  B16..8: 25.8% 
0.6%  0.2%  direct: 0.3%  skip:72.4%  L0:29.9% L1:69.0% BI: 1.1%
[libx264 @ 0x55a16881aec0] coded y,u,v intra: 12.4% 1.8% 1.2% inter: 7.0%
1.6% 0.7%
[libx264 @ 0x55a16881aec0] i16 v,h,dc,p: 51% 26% 18%  5%
[libx264 @ 0x55a16881aec0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 18% 19% 32%  5% 
6%  5%  6%  4%  5%
[libx264 @ 0x55a16881aec0] Weighted P-Frames: Y:2.9% UV:0.7%
[libx264 @ 0x55a16881aec0] ref P L0: 39.8% 52.2%  5.6%  2.3%  0.1%
[libx264 @ 0x55a16881aec0] ref B L0: 88.5%  9.1%  2.4%
[libx264 @ 0x55a16881aec0] ref B L1: 97.8%  2.2%
[libx264 @ 0x55a16881aec0] kb/s:3051.71

I can cheat by putting a colorbalance section afterwards:

  ffmpeg -i IMG_1685.MOV -q:v 0 -vcodec h264 -acodec aac -strict -2
-filter:v
format=pix_fmts=rgb24,lagfun=decay=0.999:planes=1,colorlevels=romax=0.6:bomax=0.6
greenlag2.mp4

which leads to this output http://www.robinbussell.co.uk/mov/greenlag2.mp4 
but that feels like cheating!

Can anyone help explain what's going on? I was expecting green trails but
got white. There are Blue trails too, however, from the blue LEDs in the
scene, am I getting the concept of planes mixed up somewhere? maybe
something to do with the very high contrast input?

Many thanks,
      Robin.

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