FFmpeg: Como posso definir vários arquivos de áudio?

Question

Eu quero adicionar vários arquivos de áudio ao vídeo de saída (mesclá-los em um fluxo). Cada áudio tem sua própria duração e ponto inicial / final. Eu desenhei uma imagem para explicar o que eu quero alcançar.

Eu tentei usar apad e adeley para fazer isso, mas o resultado da saída não estava correto, alguns áudios estão faltando ou não começam na hora correta.
Aqui estão os meus comandos filter_complex (os parâmetros apad and adelay nem sempre são 0.0).

-filter_complex [1] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a1]; [a1]adelay=0.0|0.0,apad[b1]; [2] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a2]; [a2]adelay=0.0|0.0[b2]; [3] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a3]; [a3]adelay=0.0|0.0,apad[b3]; [4] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a4]; [a4]adelay=0.0|0.0,apad[b4]; [5] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a5]; [a5]adelay=0.0|0.0,apad[b5]; [6] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a6]; [a6]adelay=0.0|0.0,apad[b6]; [7] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a7]; [a7]adelay=0.0|0.0,apad[b7]; [8] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a8]; [a8]adelay=0.0|0.0,apad[b8]; [9] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a9]; [a9]adelay=0.0|0.0,apad[b9]; [10] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a10]; [a10]adelay=0.0|0.0,apad[b10]; [11] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a11]; [a11]adelay=0.0|0.0,apad[b11]; [12] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a12]; [a12]adelay=0.0|0.0,apad[b12]; [13] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a13]; [a13]adelay=0.0|0.0,apad[b13]; [14] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a14]; [a14]adelay=0.0|0.0,apad[b14]; [15] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a15]; [a15]adelay=0.0|0.0,apad[b15]; [16] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a16]; [a16]adelay=0.0|0.0,apad[b16]; [17] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a17]; [a17]adelay=0.0|0.0,apad[b17]; [18] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a18]; [a18]adelay=0.0|0.0,apad[b18]; [19] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a19]; [a19]adelay=0.0|0.0,apad[b19]; [20] volume=0.0dB,aformat=sample_fmts=s16p:sample_rates=44100:channel_layouts=stereo [a20]; [a20]adelay=0.0|0.0,apad[b20]; [b1][b2][b3][b4][b5][b6][b7][b8][b9][b10][b11][b12][b13][b14][b15][b16][b17][b18][b19][b20]amerge=20[a] -map 0:v -map [a] -b:v 3200k -c:v libopenh264 -c:a aac -ac 2 /Users/Movies/test.mp4