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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 intact.
What would be the right command to accomplish this using ffmpeg?
I would appreciate your help.
Alireza
Posted 2015-10-05T09:32:33.730
Reputation: 491
77
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/
Weaver
Posted 2015-10-05T09:32:33.730
Reputation: 963
2How do you choose one specific audio track instead of delaying all audio tracks? – Freedo – 2017-10-20T06:41:58.363
1
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
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 – 2017-11-11T06:53:52.793
Well, @Freedo , as you have been already advised in https://superuser.com/questions/639402/convert-specific-video-and-audio-track-only-with-ffmpeg#comment1855076_639430 , what you suggest is in fact possible by specifying streams using metadata values, e.g.: -map 1:m:language:eng
However, bear in mind, that it will select all streams satisfying the criterium, possibly including multiple audio and/or subtitle streams. You can find more information in https://stackoverflow.com/questions/46769419/ffmpeg-choosing-audio-streams-by-language
1AFAIK -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 – 2018-03-16T14:35:31.690
@miyalys, you are right, I have shortened the codec options in the answer. However I am not sure whether the -itsoffset option affecting only video is a bug or a feature. If it is a bug, it might get fixed in a future version. – Weaver – 2018-03-18T13:33:35.173
Why does -i have to be specified two times, in the "delay audio" example? – shevy – 2018-03-29T10:32:58.353
Because we need a non-delayed input video stream and another delayed input audio stream, @shevy – Weaver – 2018-04-07T19:12:07.110
delay video command is not working.. delay audio command is working. – MathaN – 2019-03-05T12:55:29.007
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
Ivan Malyshev
Posted 2015-10-05T09:32:33.730
Reputation: 208
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
Zimba
Posted 2015-10-05T09:32:33.730
Reputation: 107
How did you find the audio delay? – Zimba – 2020-02-13T16:19:56.377