ffmpeg 2 audio files in one video file

问题:

lets say I have a video file (video.mp4) and 2 audio files (audio1.mp3 and audio2.mp3.) The video has a length of 60 seconds, every audio file has a length of 30 seconds.

What I am trying to achive is: the first 20 seconds of the video is with original audio stream, followed by 20 seconds of the first audio file (offset of 5 seconds with a length of 20s) and the same with the second audio file.

ffmpeg -i video.mp4 -ss 5 -t 20 -i audio1.mp3 -ss 5 -t 20 -i audio2.mp3 -vcodec copy -acodec copy  -copyinkf -map 0:v:0 -map 1:a:0 -map 2:a:0 -shortest final.mp4

The command above takes the video stream of the first input and the audio stream of the third input. The audio stream of the second input seems to be overwritten. How can I put all audio streams together and how can I define the offset when the audio streams should begin?

回答1:

I assume that you want the combined audio programme in one stream. Even if you applied timestamp offsets to the other audios, most players won't switch audio streams mid-playback.

So,

ffmpeg -i video.mp4 -ss 5 -t 20 -i audio1.mp3 -ss 5 -t 20 -i audio2.mp3
    -filter_complex
       "[0]atrim=0:20[a];[1]adelay=20000|20000[b];[2]adelay=40000|40000[c];[a][b][c]amix=3"
    -vcodec copy -copyinkf -shortest final.mp4