ffmpeg混音以及音视频混合

Duration = MAX(input a, v)

0. 前言

本文包括以下内容： 
（1）混音：多个音频混合 
采用amerge， amix对多个音频进行混音（而非拼接） 
（2）音视频混合——muxing 
（3）修改音频音量

1. Audio merge

1.1 amerge

-ac 2 speed up

ffmpeg -i test.mp4 -i test.mp3 -filter_complex "[0:a] [1:a]amerge=inputs=2[aout]" -map "[aout]" -ac 2 mix_amerge.aac
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PS: Without ac speed will be half.

1.2 amix

speed = amerge + ac 2

ffmpeg -i test.aac -i test.mp3 -filter_complex amix=inputs=2:duration=first:dropout_transition=2  mix.aac
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2. Simple A/V Muxer

-shortest : duration = MIN(inputs)

ffmpeg -i test.mp4 -i test.mp3 -vcodec copy -acodec aac -map 0:v:0 -map 1:a:0 -shortest mix_test.mp4
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adjust volume

ffmpeg -i test.mp4 -i test.mp3 -vcodec copy -acodec aac -map 0:v:0 -map 1:a:0 -vol 60 mix_test.mp4
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3. Complex A/V Merge (audio merge)

amerge : duration is shortest

ffmpeg -i test.mp4 -i test.mp3 -c:v copy -map 0:v:0 -filter_complex "[0:a][1:a]amerge=inputs=2[aout]" -map "[aout]" -ac 2  mix_amerge.mp4
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amix : setup duration

ffmpeg -i test.mp4 -i test.mp3 -filter_complex "[0:a][1:a]amix=inputs=2:duration=first[aout]" -map "[aout]" -c:v copy -map 0:v:0 mix_amerge.mp4
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4. Loop shorter iterm

concat shorter one

ffmpeg -i input_audio -f concat -i <(for i in {1..n}; do printf "file '%s'\n" input_video; done) -c:v copy -c:a copy -shortest output_video
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5. Adjust Volume

audio:

ffmpeg -i test.aac -i test.mp3 -filter_complex "[0:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=0.9[a0]; [1:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=0.5[a1]; [a0][a1]amerge=inputs=2[aout]" -map "[aout]" -ac 2 mix_v0.5.aac
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video:

ffmpeg -i test.mp4 -i test.mp3 -filter_complex "[0:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=0.9[a0]; [1:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=0.5[a1]; [a0][a1]amix=inputs=2:duration=first[aout]" -map "[aout]" -ac 2 -c:v copy -map 0:v:0 mix_amerge.mp4
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