[FFmpeg-user] Insert black frames -- How?

[Mark Filipak (ffmpeg)]

I'm failing on the size. I can't explain why.

 >ffmpeg -f lavfi -i color=c=black:s=1920x1080:r=60000/1001:d=60:sar=1:1 test.mkv
ffmpeg started on 2021-02-08 at 20:44:31
Report written to "ffmpeg-20210208-204431.log"
Log level: 32
ffmpeg version N-100851-g9f38fac053 Copyright (c) 2000-2021 the FFmpeg developers
   built with gcc 9.3-win32 (GCC) 20200320
   configuration: --prefix=/ffbuild/prefix --pkg-config-flags=--static --pkg-config=pkg-config 
--cross-prefix=x86_64-w64-mingw32- --arch=x86_64 --target-os=mingw32 --enable-gpl --enable-version3 
--disable-debug --disable-w32threads --enable-pthreads --enable-iconv --enable-zlib --enable-libxml2 
--enable-libfreetype --enable-libfribidi --enable-gmp --enable-lzma --enable-fontconfig 
--enable-opencl --enable-libvmaf --enable-vulkan --enable-libvorbis --enable-amf --enable-libaom 
--enable-avisynth --enable-libdav1d --enable-libdavs2 --enable-ffnvcodec --enable-cuda-llvm 
--enable-libglslang --enable-libass --enable-libbluray --enable-libmp3lame --enable-libopus 
--enable-libtheora --enable-libvpx --enable-libwebp --enable-libmfx --enable-libopencore-amrnb 
--enable-libopencore-amrwb --enable-libopenjpeg --enable-librav1e --enable-librubberband 
--enable-schannel --enable-sdl2 --enable-libsoxr --enable-libsrt --enable-libsvtav1 
--enable-libtwolame --enable-libuavs3d --enable-libvidstab --enable-libx264 --enable-libx265 
--enable-libxavs2 --enable-libxvid --enable-libzimg --extra-cflags=-DLIBTWOLAME_STATIC 
--extra-cxxflags= --extra-ldflags=-pthread --extra-libs=-lgomp
   libavutil      56. 64.100 / 56. 64.100
   libavcodec     58.119.100 / 58.119.100
   libavformat    58. 65.101 / 58. 65.101
   libavdevice    58. 11.103 / 58. 11.103
   libavfilter     7.100.100 /  7.100.100
   libswscale      5.  8.100 /  5.  8.100
   libswresample   3.  8.100 /  3.  8.100
   libpostproc    55.  8.100 / 55.  8.100
[color @ 0000029f0c0bda80] Unable to parse option value "1" as image size
     Last message repeated 1 times
[color @ 0000029f0c0bda80] Error setting option size to value 1.
[Parsed_color_0 @ 0000029f0c0bd980] Error applying options to the filter.
[lavfi @ 0000029f0c0b9000] Error initializing filter 'color' with args 
'c=black:s=1920x1080:r=60000/1001:d=60:sar=1:1'
color=c=black:s=1920x1080:r=60000/1001:d=60:sar=1:1: Invalid argument

 >ffmpeg -f lavfi -i color=c=black:s=hd1080:r=60000/1001:d=60:sar=1:1 test.mkv
ffmpeg started on 2021-02-08 at 20:44:48
Report written to "ffmpeg-20210208-204448.log"
Log level: 32
ffmpeg version N-100851-g9f38fac053 Copyright (c) 2000-2021 the FFmpeg developers
   built with gcc 9.3-win32 (GCC) 20200320
   configuration: --prefix=/ffbuild/prefix --pkg-config-flags=--static --pkg-config=pkg-config 
--cross-prefix=x86_64-w64-mingw32- --arch=x86_64 --target-os=mingw32 --enable-gpl --enable-version3 
--disable-debug --disable-w32threads --enable-pthreads --enable-iconv --enable-zlib --enable-libxml2 
--enable-libfreetype --enable-libfribidi --enable-gmp --enable-lzma --enable-fontconfig 
--enable-opencl --enable-libvmaf --enable-vulkan --enable-libvorbis --enable-amf --enable-libaom 
--enable-avisynth --enable-libdav1d --enable-libdavs2 --enable-ffnvcodec --enable-cuda-llvm 
--enable-libglslang --enable-libass --enable-libbluray --enable-libmp3lame --enable-libopus 
--enable-libtheora --enable-libvpx --enable-libwebp --enable-libmfx --enable-libopencore-amrnb 
--enable-libopencore-amrwb --enable-libopenjpeg --enable-librav1e --enable-librubberband 
--enable-schannel --enable-sdl2 --enable-libsoxr --enable-libsrt --enable-libsvtav1 
--enable-libtwolame --enable-libuavs3d --enable-libvidstab --enable-libx264 --enable-libx265 
--enable-libxavs2 --enable-libxvid --enable-libzimg --extra-cflags=-DLIBTWOLAME_STATIC 
--extra-cxxflags= --extra-ldflags=-pthread --extra-libs=-lgomp
   libavutil      56. 64.100 / 56. 64.100
   libavcodec     58.119.100 / 58.119.100
   libavformat    58. 65.101 / 58. 65.101
   libavdevice    58. 11.103 / 58. 11.103
   libavfilter     7.100.100 /  7.100.100
   libswscale      5.  8.100 /  5.  8.100
   libswresample   3.  8.100 /  3.  8.100
   libpostproc    55.  8.100 / 55.  8.100
[color @ 00000211a0d7da80] Unable to parse option value "1" as image size
     Last message repeated 1 times
[color @ 00000211a0d7da80] Error setting option size to value 1.
[Parsed_color_0 @ 00000211a0d7d980] Error applying options to the filter.
[lavfi @ 00000211a0d79000] Error initializing filter 'color' with args 
'c=black:s=hd1080:r=60000/1001:d=60:sar=1:1'
color=c=black:s=hd1080:r=60000/1001:d=60:sar=1:1: Invalid argument