Mixing an audio and video file together using FFMPEG causes desync

Question

Premiere Pro won't render properly, so I've let it render the m4v and aac files then combine them using ffmpeg.

ffmpeg -i "MCU- Supercut P1.24076.65056.m4v" -i "MCU- Supercut P1.24076.65056.aac" -c copy "MCU-Supercut-P1-FINAL.mp4"

This works but the audio desyncs from the video. I assume this is because the video doesn't have a listed length in the metadata, I know the length of the video but I'm not sure how to make ffmpeg follow that.

Answer 1

ffmpeg -i "MCU- Supercut P1.24076.65056.m4v" -c:a acc -i "MCU- Supercut P1.24076.65056.aac"    -c copy -map 0:v -map 1:a:0   -disposition:a:0 default  -strict -2 -sn -dn -map_metadata -1 -map_chapters -1  -movflags faststart fin_av.mp4