Uniting various mp4 with various mp3 using ffmpeg

Question

I have 50 parts of mp3 audio files and 50 parts of mp4 video files (without audio) files, which I want to unite into one video. I tried uniting the audio files into one file, then uniting the videos into one file, and eventually unting it all to one video with the following command. I used this How to merge audio and video file in ffmpeg.

ffmpeg.exe -f concat -safe 0 -i video_list.txt -c:v video.mp4

ffmpeg.exe -f concat -safe 0 -i audio_list.txt -c:a audio.mp3

ffmpeg.exe -i video.mp4 -i audio.mp3 -c:v copy -c:a aac final.mkv

All tryings led to the video being played before the audio in final.mkv (audio delayed).

Am I doing it wrong?

Answer 1

Eventually I succeeded by uniting each video with the suitable audio with the -shortest ffmpeg option. That's made ffmpeg stop encoding once one file ends. Then I united all the videos that were created together. Thanks for the help.