ffmpeg throw a silent video output when trying to merge video and audio - audio

Question

I tried to combine mp4 format video and wav format audio.
The video is shorter than the audio and start second is same as 00:00.
I used command as bellows:
ffmpeg -i video.mp4 -i audio.wav -filter_complex "[0:a]volume=0.2[A];[1:a][A]amerge[Aout]" -map 0:v -map [Aout] -y -shortest output_video.mp4
The problem is the output_video.mp4 is a silent video without the sound.
How can I get the output_video.mp4 with sound from audio.wav?
ffmpeg output is:
ffmpeg version 4.2.2 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 7.3.0 (crosstool-NG 1.23.0.449-a04d0)
configuration: --prefix=/tmp/build/80754af9/ffmpeg_1587154242452/\_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeho --cc=/tmp/build/80754af9/ffmpeg_1587154242452/\_build_env/bin/x86_64-conda_cos6-linux-gnu-cc --disable-doc --enable-avresample --enable-gmp --enable-hardcoded-tables --enable-libfreetype --enable-libvpx --enable-pthreads --enable-libopus --enable-postproc --enable-pic --enable-pthreads --enable-shared --enable-static --enable-version3 --enable-zlib --enable-libmp3lame --disable-nonfree --enable-gpl --enable-gnutls --disable-openssl --enable-libopenh264 --enable-libx264
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
libavresample 4. 0. 0 / 4. 0. 0
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 'video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.29.100
Duration: 00:00:19.04, start: 0.000000, bitrate: 510 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 373 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : SoundHandler
Guessed Channel Layout for Input Stream #1.0 : mono
Input #1, wav, from 'audio.wav':
Duration: 00:00:14.70, bitrate: 352 kb/s
Stream #1:0: Audio: pcm_s16le (\[1\]\[0\]\[0\]\[0\] / 0x0001), 22050 Hz, mono, s16, 352 kb/s
Stream mapping:
Stream #0:1 (aac) -\> volume (graph 0)
Stream #1:0 (pcm_s16le) -\> amerge:in0 (graph 0)
Stream #0:0 -\> #0:0 (h264 (native) -\> h264 (libx264))
amerge (graph 0) -\> Stream #0:1 (aac)
Press \[q\] to stop, \[?\] for help
\[libx264 # 0x55aa9a642ac0\] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
\[libx264 # 0x55aa9a642ac0\] profile High, level 3.1, 4:2:0, 8-bit
\[libx264 # 0x55aa9a642ac0\] 264 - core 157 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - 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=-2 threads=22 lookahead_threads=3 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=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
\[Parsed_amerge_1 # 0x55aa9b37c140\] No channel layout for input 1
Output #0, mp4, to 'output_video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.29.100
Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 1280x720, q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
Metadata:
handler_name : VideoHandler
encoder : Lavc58.54.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 22050 Hz, 3.0, fltp, 197 kb/s (default)
Metadata:
encoder : Lavc58.54.100 aac
frame= 507 fps=291 q=-1.0 Lsize= 1116kB time=00:00:16.80 bitrate= 544.3kbits/s speed=9.64x
video:760kB audio:342kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.242977%
\[libx264 # 0x55aa9a642ac0\] frame I:3 Avg QP:16.24 size: 19770
\[libx264 # 0x55aa9a642ac0\] frame P:154 Avg QP:20.29 size: 3227
\[libx264 # 0x55aa9a642ac0\] frame B:350 Avg QP:19.84 size: 633
\[libx264 # 0x55aa9a642ac0\] consecutive B-frames: 0.6% 15.8% 18.9% 64.7%
\[libx264 # 0x55aa9a642ac0\] mb I I16..4: 23.5% 67.4% 9.1%
\[libx264 # 0x55aa9a642ac0\] mb P I16..4: 0.7% 3.0% 0.3% P16..4: 13.0% 3.1% 1.0% 0.0% 0.0% skip:78.8%
\[libx264 # 0x55aa9a642ac0\] mb B I16..4: 0.2% 0.1% 0.0% B16..8: 10.4% 0.3% 0.0% direct: 0.6% skip:88.3% L0:41.5% L1:57.2% BI: 1.3%
\[libx264 # 0x55aa9a642ac0\] 8x8 transform intra:68.2% inter:81.9%
\[libx264 # 0x55aa9a642ac0\] coded y,uvDC,uvAC intra: 24.6% 22.9% 6.1% inter: 1.2% 1.7% 0.0%
\[libx264 # 0x55aa9a642ac0\] i16 v,h,dc,p: 68% 16% 6% 10%
\[libx264 # 0x55aa9a642ac0\] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 10% 50% 2% 2% 3% 2% 4% 3%
\[libx264 # 0x55aa9a642ac0\] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 25% 13% 5% 5% 6% 5% 6% 4%
\[libx264 # 0x55aa9a642ac0\] i8c dc,h,v,p: 75% 10% 12% 2%
\[libx264 # 0x55aa9a642ac0\] Weighted P-Frames: Y:0.0% UV:0.0%
\[libx264 # 0x55aa9a642ac0\] ref P L0: 65.9% 16.2% 13.5% 4.4%
\[libx264 # 0x55aa9a642ac0\] ref B L0: 84.1% 13.4% 2.5%
\[libx264 # 0x55aa9a642ac0\] ref B L1: 97.1% 2.9%
\[libx264 # 0x55aa9a642ac0\] kb/s:368.24
\[aac # 0x55aa9a62a280\] Qavg: 8290.713

Answer 1

There's no need to mess about with filter_complex, you are not changing anything. You simply want to map the video from one source to the audio from another.
ffmpeg -i input.mp4 -i input.wav -shortest -map 0:v -map 1:a out.mp4
should achieve what you require.