Valid Slideshow-Video created by ffmpeg is not accepted by Twitter

I create a video from a slideshow using ffmpeg. I have a valid video at the end. VLC plays that video, YouTube also. I want to display the final product directly on twitter.

I checked the recommened specs according to resolution, framerate, aspect ration and size required for Twitter to accept this video. But still when trying to add this video direcectly into Twitter I receive an error that "no video with supported format or MIME-Type found".

Ffmpeg does not display any error or warning.

Arguments:

ffmpeg -f image2pipe -framerate 1 -i pipe:.png -c:v libx264 -crf 21  -r 30 -y "Blathering.noaudio.mp4"

As you can see I create one image per frame (-framerate 1) but create a 30fps output file (-r 30)

The output from ffmpeg looks like this:

ffmpeg version git-2020-06-17-0b3bd00 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9.3.1 (GCC) 20200523
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 55.100 / 56. 55.100
  libavcodec     58. 92.100 / 58. 92.100
  libavformat    58. 46.101 / 58. 46.101
  libavdevice    58. 11.100 / 58. 11.100
  libavfilter     7. 86.100 /  7. 86.100
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Input #0, image2pipe, from 'pipe:.png':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: png, rgba(pc), 680x420 [SAR 3779:3779 DAR 34:21], 1 fps, 1 tbr, 1 tbn, 1 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
[libx264 @ 00000217ad682780] using SAR=1/1
[libx264 @ 00000217ad682780] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 00000217ad682780] profile High 4:4:4 Predictive, level 3.0, 4:4:4, 8-bit
[libx264 @ 00000217ad682780] 264 - core 160 - H.264/MPEG-4 AVC codec - Copyleft 2003-2020 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 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=21.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'Blathering.noaudio.mp4':
  Metadata:
    encoder         : Lavf58.46.101
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv444p, 680x420 [SAR 1:1 DAR 34:21], q=-1--1, 30 fps, 15360 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.92.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
frame=  150 fps=0.0 q=-1.0 Lsize=      17kB time=00:00:04.90 bitrate=  29.2kbits/s dup=145 drop=0 speed=  29x
video:15kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 17.439800%
[libx264 @ 00000217ad682780] frame I:1     Avg QP:12.52  size:  9283
[libx264 @ 00000217ad682780] frame P:38    Avg QP:10.45  size:    53
[libx264 @ 00000217ad682780] frame B:111   Avg QP:11.67  size:    29
[libx264 @ 00000217ad682780] consecutive B-frames:  1.3%  0.0%  0.0% 98.7%
[libx264 @ 00000217ad682780] mb I  I16..4: 66.0% 25.8%  8.3%
[libx264 @ 00000217ad682780] mb P  I16..4:  0.0%  0.0%  0.0%  P16..4:  0.0%  0.0%  0.0%  0.0%  0.0%    skip:99.9%
[libx264 @ 00000217ad682780] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  0.5%  0.0%  0.0%  direct: 0.0%  skip:99.5%  L0:64.2% L1:35.8% BI: 0.0%
[libx264 @ 00000217ad682780] 8x8 transform intra:25.9% inter:0.0%
[libx264 @ 00000217ad682780] coded y,u,v intra: 5.2% 3.2% 3.1% inter: 0.0% 0.0% 0.0%
[libx264 @ 00000217ad682780] i16 v,h,dc,p: 89% 11%  0%  0%
[libx264 @ 00000217ad682780] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 60%  4% 36%  0%  0%  0%  0%  0%  0%
[libx264 @ 00000217ad682780] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 27% 36% 19%  2%  3%  3%  5%  2%  4%
[libx264 @ 00000217ad682780] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 00000217ad682780] ref P L0: 86.2%  3.4% 10.3%
[libx264 @ 00000217ad682780] ref B L0: 51.9% 48.1%
[libx264 @ 00000217ad682780] kb/s:23.31

The Codec information are the following:

This is pure Images, no audio at this point in the video. Is there a parameter I am missing? IMHO this looks like a very common video file I create there.