ffmpeg: join + crossfade 5 input files (video+audio) into one output file - ffmpeg

Question

I have 5 mp4 input videos (audio+video) that I want to 'join' into a single output video with a crossfade effect in between each pair of videos.
I want to 'crossfade' both the audio and the video, with a transition of 0.4s.
(Not an actual crossfade, more like video-2 fades in over video-1, video-1 does not need to fade out, but this is not the problem)
I'm using ffmpeg-4.1.3-win64-static
I have followed many tutorials and answers from here, but there are so many different ways to do it...
Each one of the 5 videos is 1.024s long, duration obtained with ffprobe
ffprobe.exe -i "0.mp4" -show_entries format=duration -v quiet -of csv="p=0"
This is the command for both audio and video:
(I've reformatted the command so it is easier to read, it is issued as a single line in the command prompt)
ffmpeg.exe -y -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4"
-filter_complex "
[0:v]setpts=PTS-STARTPTS[v1];
[1:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(0.6/TB)[v2];
[2:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.2/TB)[v3];
[3:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.8/TB)[v4];
[4:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(2.4/TB)[v5];
[v1][v2]overlay[u1];[u1][v3]overlay[u2];[u2][v4]overlay[u3];[u3][v5]overlay,format=yuv420p[v];
[0][1]acrossfade=d=0.4[a0];
[a0][2]acrossfade=d=0.4[a1];
[a1][3]acrossfade=d=0.4[a2];
[a2][4]acrossfade=d=0.4[a]
" -map [v] -map [a] "output.mp4"
When I do both audio and video into a single output file, output.mp4 can not be played on VLC, this is the vlc log:
main debug: `file:///C:/project/input-videos/output.mp4' gives access `file' demux `any' path `/C:project/input-videos/output.mp4'
main debug: creating demux: access='file' demux='any' location='/C:/project/input-videos/output.mp4' file='C:\project\input-videos\output.mp4'
main debug: looking for access_demux module matching "file": 15 candidates
main debug: no access_demux modules matched
main debug: creating access: file:///C:/project/input-videos/output.mp4
main debug: (path: C:\project\input-videos\output.mp4)
main debug: looking for access module matching "file": 26 candidates
main debug: using access module "filesystem"
main debug: looking for stream_filter module matching "prefetch,cache_read": 24 candidates
cache_read debug: Using stream method for AStream*
cache_read debug: starting pre-buffering
cache_read error: cannot pre fill buffer
main debug: looking for meta fetcher module matching "any": 1 candidates
main debug: no stream_filter modules matched
main warning: cannot insert stream filter prefetch,cache_read
main debug: looking for stream_filter module matching "any": 24 candidates
playlist debug: not enough data
...
This is the output from ffmpeg:
ffmpeg version 4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 8.3.1 (GCC) 20190414
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --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-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth
libavutil 56. 22.100 / 56. 22.100
libavcodec 58. 35.100 / 58. 35.100
libavformat 58. 20.100 / 58. 20.100
libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100
libpostproc 55. 3.100 / 55. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '0.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
location-eng : +52.6899-001.8293/
location : +52.6899-001.8293/
Duration: 00:00:01.02, start: 0.000000, bitrate: 13821 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 14002 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandle
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : SoundHandle
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '1.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
location-eng : +53.4256-001.3580/
location : +53.4256-001.3580/
Duration: 00:00:01.02, start: 0.000000, bitrate: 7094 kb/s
Stream #1:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 7113 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandle
Stream #1:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : SoundHandle
Input #2, mov,mp4,m4a,3gp,3g2,mj2, from '2.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
location-eng : +53.3927-001.5044/
location : +53.3927-001.5044/
Duration: 00:00:01.02, start: 0.000000, bitrate: 7367 kb/s
Stream #2:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 7394 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandle
Stream #2:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 126 kb/s (default)
Metadata:
handler_name : SoundHandle
Input #3, mov,mp4,m4a,3gp,3g2,mj2, from '3.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
location-eng : +53.3927-001.5044/
location : +53.3927-001.5044/
Duration: 00:00:01.02, start: 0.000000, bitrate: 8145 kb/s
Stream #3:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 8192 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandle
Stream #3:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 125 kb/s (default)
Metadata:
handler_name : SoundHandle
Input #4, mov,mp4,m4a,3gp,3g2,mj2, from '4.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.20.100
location-eng : +53.3927-001.5044/
location : +53.3927-001.5044/
Duration: 00:00:01.02, start: 0.000000, bitrate: 6241 kb/s
Stream #4:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2224x1080 [SAR 1:1 DAR 278:135], 6241 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandle
Stream #4:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 126 kb/s (default)
Metadata:
handler_name : SoundHandle
Stream mapping:
Stream #0:0 (h264) -> setpts
Stream #0:1 (aac) -> acrossfade:crossfade0
Stream #1:0 (h264) -> format
Stream #1:1 (aac) -> acrossfade:crossfade1
Stream #2:0 (h264) -> format
Stream #2:1 (aac) -> acrossfade:crossfade1
Stream #3:0 (h264) -> format
Stream #3:1 (aac) -> acrossfade:crossfade1
Stream #4:0 (h264) -> format
Stream #4:1 (aac) -> acrossfade:crossfade1
format -> Stream #0:0 (libx264)
acrossfade -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
When I do the video only it is fine. The duration of the output.mp4 file generated for video-only is 3.4s
When I do the audio only it is also fine. The duration of the output.mp4 file generated for audio-only is 3.435s
This is the command for video only:
ffmpeg.exe -y -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4"
-filter_complex "
[0:v]setpts=PTS-STARTPTS[v1];
[1:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(0.6/TB)[v2];
[2:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.2/TB)[v3];
[3:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(1.8/TB)[v4];
[4:v]format=yuva420p,fade=in:st=0:d=0.4:alpha=1,setpts=PTS-STARTPTS+(2.4/TB)[v5];
[v1][v2]overlay[u1];[u1][v3]overlay[u2];[u2][v4]overlay[u3];[u3][v5]overlay,format=yuv420p[v]
" -map [v] "output.mp4"
This is the command for audio only:
ffmpeg.exe -y -i "0.mp4" -i "1.mp4" -i "2.mp4" -i "3.mp4" -i "4.mp4"
-filter_complex "
[0][1]acrossfade=d=0.4[a0];
[a0][2]acrossfade=d=0.4[a1];
[a1][3]acrossfade=d=0.4[a2];
[a2][4]acrossfade=d=0.4[a]
" -map [a] "output.mp4"
What am I missing in order to generate one output file with both audio and video content?
Edit: Here's the full ffmpeg command + result for audio and video combined with "-loglevel debug" added. (Too big to add directly here, so I've added it to Pastebin)
https://pastebin.com/NLBc7Abb
Work Around
Not a solution, but I found a work around:
Create video only output using command above, output to video.mp4
Create audio only output using command above, output to audio.mp4
Merge both video.mp4 and audio.mp4 into output.mp4 using the following command:
ffmpeg.exe -y -i "video.mp4" -i "audio.mp4" -c:v copy -c:a aac output.mp4
If anyone has any ideas as to why the combined audio+video command does not work, please let me know. :)