add black&silence to beginning of a video - audio

Question

Hi I am struggling to add black&silence to the begining of a video with ffmpeg. I did search a lot but they look too complex for me.
Below command is what I find to add black&silence to the end of of video, now how can I tune it to the beginning of a video?
ffmpeg -i input.mp4 -f lavfi -i color=s=1920x1080:d=10 -filter_complex [0:v][1]concat -af [0]apad -shortest output.mp4
Looks I need to use adelay instead of apad, below is the command that makes sense to me, but the audio is not delayed.
ffmpeg -i input.mp4 -f lavfi -i color=s=1920x1080:d=10 -filter_complex [1][0:v]concat -af [0]adelay=10 output.mp4
Here is the input info and ffmpeg version:
ffmpeg -i input.mp4
ffmpeg version 4.2.1-static https://johnvansickle.com/ffmpeg/ Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
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
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 'input.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.29.100
Duration: 00:01:00.00, start: 0.000998, bitrate: 2526 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080, 2394 kb/s, 24 fps, 24 tbr, 16k tbn, 48 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 124 kb/s (default)
Metadata:
handler_name : SoundHandler
At least one output file must be specified
Thanks!

Answer 1

There are several methods to do this. The first method is simple and easy but re-encodes the main video. The other method is slightly more complicated but does not re-encode the main video, so the quality is preserved this method will be faster for long videos.
tpad & adelay filters
Using the tpad and adelay filters:
ffmpeg -i input.mp4 -filter_complex "[0:v]tpad=start_duration=2[v];[0:a]adelay=2s:all=true[a]" -map "[v]" -map "[a]" output.mp4
If your ffmpeg is older than version 4.2 then change adelay=2s:all=true to adelay=2000|2000.
color & anullsrc filters with concat demuxer
Make 2 second black and silence that match the attributes of the input. Using the color and anullsrc filters:
ffmpeg -f lavfi -i color=size=1920x1080:rate=24:duration=2 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 -video_track_timescale 16k -shortest black.mp4
Make join.txt containing:
file 'black.mp4'
file 'input.mp4'
Concatenate with the concat demuxer:
ffmpeg -f concat -i join.txt -c copy output.mp4