[FFmpeg-user] ffmpeg MP4/x264 output colours change when input source is different resolution (bug?)

Wed Sep 14 13:12:25 EEST 2022

On 9/14/22, Dan <twinbee42 at skytopia.com> wrote:
> Using the latest 5.1.1 "essentials build" by www.gyan.dev.
>
> Hi all, I'm a beginner to ffmpeg so I'm having a hard time believing that a
> utility so old and so widely used has such a fundamental bug, but the
> evidence is staring me in the face and leads me to no other conclusion.
>
> It's incredibly easy to replicate thankfully. I want to convert numerous
> frames to make an animation, but thankfully, I've simplified the problem to
> even using a single image to make a '1 frame video' for the purposes of
> debugging.
>
> Simply perform this command line:

Scale filter may give different colors depending on frame dimensions.

Use zscale filter instead.

>
> ffmpeg.exe -i original.png -crf 0 -vcodec libx264 output.mp4
>
> ...With this "original.png" ("fC2Tj") image:
> https://i.stack.imgur.com/5jkct.png
>
> And this command line:
>
> ffmpeg.exe -i doubleHeight.png -crf 0 -vcodec libx264 output.mp4
>
> ...On this "doubleHeight" ("RGIvA") image:
> https://i.stack.imgur.com/PLdsb.png
>
> The double height version is darker than it should be. I've checked the
> resulting video in both Media Player Classic and Chrome.
>
> If you check the dark green colour on the original PNG images, using an eye
> dropper tool, they're both R=25,G=74,B=15. However, if you check the same
> colour on the output MP4s, the colour matches on the original PNG, but not
> the doubleHeight version, which is R=22,G=66,B=12.
>
> If I use -vcodec libx264rgb, instead of -vcodec libx264, that fixes the
> issue, but I need libx264 so the output video can work on Chrome and other
> media players.
>
> What gives? CLI output below (for the double height version):
>
> -------------------------------------------------------------------------------
>
> D:\Utils\ffmpeg\bin\ffmpeg.exe -i
> C:\Users\<USERNAME>\Desktop\testcol\PLdsb.png -crf 0 -vcodec libx264
> C:\Users\<USERNAME>\Desktop\testcol\PLdsb.mp4
> ffmpeg version 5.1.1-essentials_build-www.gyan.dev Copyright (c) 2000-2022
> the FFmpeg developers
>    built with gcc 12.1.0 (Rev2, Built by MSYS2 project)
>    configuration: --enable-gpl --enable-version3 --enable-static
> --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv
> --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-zlib
> --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth
> --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265
> --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx
> --enable-libass --enable-libfreetype --enable-libfribidi --enable-libvidstab
> --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm
> --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc
> --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libgme
> --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame
> --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm
> --enable-libopencore-amrnb --enable-libopus --enable-libspeex
> --enable-libvorbis --enable-librubberband
>    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, png_pipe, from 'C:\Users\<USERNAME>\Desktop\testcol\PLdsb.png':
>    Duration: N/A, bitrate: N/A
>    Stream #0:0: Video: png, rgb24(pc), 968x984, 25 fps, 25 tbr, 25 tbn
> Stream mapping:
>    Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
> Press [q] to stop, [?] for help
> [libx264 @ 000001b24acb3400] using cpu capabilities: MMX2 SSE2Fast SSSE3
> SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
> [libx264 @ 000001b24acb3400] profile High 4:4:4 Predictive, level 3.2,
> 4:4:4, 8-bit
> [libx264 @ 000001b24acb3400] 264 - core 164 r3095 baee400 - H.264/MPEG-4 AVC
> codec - Copyleft 2003-2022 - http://www.videolan.org/x264.html - options:
> cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=0
> mixed_ref=1 me_range=16 chroma_me=1 trellis=0 8x8dct=1 cqm=0 deadzone=21,11
> fast_pskip=0 chroma_qp_offset=0 threads=12 lookahead_threads=2
> sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0
> constrained_intra=0 bframes=0 weightp=2 keyint=250 keyint_min=25 scenecut=40
> intra_refresh=0 rc=cqp mbtree=0 qp=0
> Output #0, mp4, to 'C:\Users\<USERNAME>\Desktop\testcol\PLdsb.mp4':
>    Metadata:
>      encoder         : Lavf59.27.100
>    Stream #0:0: Video: h264 (avc1 / 0x31637661), yuv444p(tv, progressive),
> 968x984, q=2-31, 25 fps, 12800 tbn
>      Metadata:
>        encoder         : Lavc59.37.100 libx264
>      Side data:
>        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
> frame=    1 fps=0.0 q=0.0 Lsize=       2kB time=00:00:00.00
> bitrate=180512.8kbits/s speed=0.0017x
> video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing
> overhead: 88.235291%
> [libx264 @ 000001b24acb3400] frame I:1     Avg QP: 0.00  size:   405
> [libx264 @ 000001b24acb3400] mb I  I16..4: 83.5% 16.4%  0.1%
> [libx264 @ 000001b24acb3400] 8x8 transform intra:16.4%
> [libx264 @ 000001b24acb3400] coded y,u,v intra: 0.0% 0.0% 0.0%
> [libx264 @ 000001b24acb3400] i16 v,h,dc,p: 100%  0%  0%  0%
> [libx264 @ 000001b24acb3400] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 41%  0% 59%  0%
> 0%  0%  0%  0%  0%
> [libx264 @ 000001b24acb3400] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 38%  6% 56%  0%
> 0%  0%  0%  0%  0%
> [libx264 @ 000001b24acb3400] kb/s:81.00
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