In ffmpeg, how to delay only the audio of a .mp4 video without converting the audio?

In my .mp4 file the audio delay is -3840 ms. I synced it in KMplayer, and I don't want to use MKVGUI to make a .mkv file. I just need to delay the audio by 3840 ms, everything else should be left intact.
What would be the right command to accomplish this using ffmpeg?
I would appreciate your help.

Solution 1:

If you need to delay video by 3.84 seconds, use a command like this:

ffmpeg.exe -i "movie.mp4" -itsoffset 3.84 -i "movie.mp4" -map 1:v -map 0:a -c copy "movie-video-delayed.mp4"

If you need to delay audio by 3.84 seconds, use a command like this:

ffmpeg.exe -i "movie.mp4" -itsoffset 3.84 -i "movie.mp4" -map 0:v -map 1:a -c copy "movie-audio-delayed.mp4"

Make sure, that your ffmpeg build is not too old, newer than 2012 will suffice.

Explanation

-itsoffset 3.84 -i "movie.mp4"

Offsets timestamps of all streams by 3.84 seconds in the input file that follows the option (movie.mp4).

-map 1:v -map 0:a

Takes video stream from the second (delayed) input and audio stream from the first input - both inputs may of course be the same file.

A more verbose explanation can be found here:
http://alien.slackbook.org/blog/fixing-audio-sync-with-ffmpeg/

Solution 2:

Make first silence audio:

ffmpeg -f lavfi -i anullsrc=channel_layout=5.1:sample_rate=48000 -t 3 silence_3_sec.mp3

Then concat files:

ffmpeg -i "concat:silence_3_sec.mp3|input.mp3" -acodec copy out.mp3