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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.

  • How did you find the audio delay? – Zimba Feb 13 at 16:19
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    In my .mp4 file the audio delay is -3840 ms. ... I just need to delay the audio by -3840 ms, it's a bit contradictory: between the number of the present delay and the number of the needed delay, one and only one of them has to be negative. – cipricus Mar 21 at 11:35
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    You are right @cipricus, I removed the minus sign in front of the second delay amount. – Weaver Mar 22 at 16:19
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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/

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    How do you choose one specific audio track instead of delaying all audio tracks? – Freedo Oct 20 '17 at 6:41
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    Using the capabilities of map option. You first need to find the index of the desired audio stream in the input file using any of these commands: ffprobe.exe "input_file.mp4" or ffmpeg.exe -i "input_file.mp4" Let's suppose that the index of the audio stream to be delayed is 2 (i.e. the third stream) and that the delayed input is the second one (as in my example). To delay only the third stream, take all other streams from the first input and only the one audio stream from the second (delayed) input: -map 0:0 -map 0:1 -map 1:2 – Weaver Oct 22 '17 at 15:03
  • that's kind not what I meant. In this case i still have to call ffmpeg and parse the results to do find the indexes. Is there a equivalent to say -map eng – Freedo Nov 11 '17 at 6:53
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    AFAIK -c copy can be used instead of -vcodec copy -acodec copy, and itsoffset only affects video, so maybe this would work the same?: ffmpeg -i "movie.mp4" -itsoffset 3.84 -c copy "movie-video-delayed.mp4" and to delay the audio instead simply add a negative sign to the duration: -3.84. – miyalys Mar 16 '18 at 14:35
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    Definitely not @cipricus. Both commands work according to their respective descriptions, I tested them on ffmpeg ver. 4.0.2. – Weaver Mar 22 at 16:11
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
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0

I extracted audio with Audacity, then cut some silence (equal to delay) from end of video, and added to beginning of audio.
After doing any other adjustments to audio eg. normalization, I exported audio, and replaced audio in original via ffmpeg:

ffmpeg-i "in.mp4" -i "synced.m4a" -vcodec copy -acodec copy -map 0:0 -map 1:0 out.mp4

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