ffmpeg: How to avoid "start: 0.033333" when extraction audio from mp4
Correction: instead of

ffmpeg -i output-audio.mp4 -i output-video.mp4 test-combine.mp4


it should be

ffmpeg -i output-audio.mp4 -i output-video.mp4 -shortest output-combine.mp4


Kind of answer:

ffmpeg -i output-video.mp4 -itsoffset 0.033333 -t 9.966666 -i output-audio.mp4  output-combine.mp4


seems to do the job, although the result differs in file-size slightly from an direct extraction (direct is bigger than combine) done with

ffmpeg -accurate_seek -ss 30 -t 10 -i input.mp4 output-direct.mp4