Aligning sound to video ... how?

gael33 · 09-28-2014, 07:56 AM

I have a MP4 short video from a wedding the video is crystal clear but the sound is out of alignment by about 6 secs.
Does anyone know of a program that I could use to bring the sound back into alignment with the video?
I have had a look at Pitivi and Openshot and I cannot figure out how to use them (I'm not stupid, I'm just getting on in years).
Any help will be appreciated,
Thanks.

Pearlseattle · 09-28-2014, 11:42 AM

You probably just want to remux it so as to not lose quality, right?
if yes then there are probably a lot of tools that can do it, e.g. mmg (part of mkvtoolnix) (but the output container format will then be mkv instead of mp4), avidemux, etc... .

teckk · 09-28-2014, 04:34 PM

If you are serious I will show you how to do that. My examples will be with mplayer and ffmpeg, but you can use what you wish.

You will first need to determine exactly how far out of sync the audio and video is. You could do that with mplayer. Play the video while pressing the + or - keys watching the on screen display until you have the audio video in sync. Note how far out of sync it is. Then dump the audio to a file, dump the video to another file. Then put them back together while syncing the A-V. Also find out what audio codec the video has.

Read the output of

Code:

ffmpeg -i yourfile.mp4

I'll use .aac as an example with an out of sync by 6.1 seconds.

Code:

ffmpeg -i yourfile.mp4 -vn -c:a copy outaud.aac

Code:

ffmpeg -i yourfile.mp4 -an -c:v copy outvid.mp4

Then put them back together with an offset and copying the input. Use positive or negative offset depending on which way you need to go. You may need a little trial and error to get the sync exact. You can delay the audio or the video. -itsoffset comes before the file that wish to offset.

Code:

ffmpeg -i outvid.mp4 -itsoffset 6.1 -i outaud.aac -c copy Newfile.mp4

Look at man ffmpeg

https://trac.ffmpeg.org/wiki/TitleIndex
https://www.ffmpeg.org/ffmpeg.html
http://linux.die.net/man/1/ffmpeg

After you have made an attempt to solve it, and have a Newfile.mp4, and need more help...ask.

gael33 · 09-28-2014, 05:05 PM

Quote:

Originally Posted by teckk

If you are serious I will show you how to do that. My examples will be with mplayer and ffmpeg, but you can use what you wish.

You will first need to determine exactly how far out of sync the audio and video is. You could do that with mplayer. Play the video while pressing the + or - keys watching the on screen display until you have the audio video in sync. Note how far out of sync it is. Then dump the audio to a file, dump the video to another file. Then put them back together while syncing the A-V. Also find out what audio codec the video has.

Read the output of

Code:

ffmpeg -i yourfile.mp4

I'll use .aac as an example with an out of sync by 6.1 seconds.

Code:

ffmpeg -i yourfile.mp4 -vn -c:a copy outaud.aac

Code:

ffmpeg -i yourfile.mp4 -an -c:v copy outvid.mp4

Then put them back together with an offset and copying the input. Use positive or negative offset depending on which way you need to go. You may need a little trial and error to get the sync exact. You can delay the audio or the video. -itsoffset comes before the file that wish to offset.

Code:

ffmpeg -i outvid.mp4 -itsoffset 6.1 -i outaud.aac -c copy Newfile.mp4

Look at man ffmpeg

https://trac.ffmpeg.org/wiki/TitleIndex
https://www.ffmpeg.org/ffmpeg.html
http://linux.die.net/man/1/ffmpeg

After you have made an attempt to solve it, and have a Newfile.mp4, and need more help...ask.

I really do appreciate all that information, but as pensioner/silver surfer with not a lot of techie know-how I would be frightened to even attempt that.
I noticed that VLC player can adjust sound sync ... is it possible to use that program and save the adjusted file?

ondoho · 09-29-2014, 04:53 AM

Quote:

Originally Posted by gael33

frightened to even attempt that.

why on earth?
are you frightened to use your keyboard instead of your mouse?
just copy the file(s) to a dedicated folder, open a terminal in that folder and try it. if it doesn't work, remove the folder. there.

gael33 · 09-29-2014, 05:49 AM

Quote:

Originally Posted by ondoho

why on earth?
are you frightened to use your keyboard instead of your mouse?
just copy the file(s) to a dedicated folder, open a terminal in that folder and try it. if it doesn't work, remove the folder. there.

Okay, I'll give it a go later

teckk · 09-29-2014, 02:51 PM

Oh course if you were a Linux geek you might make a bash script to automate all of that. There are 50 ways to do this, something like:

offset.sh

Code:

#! /usr/bin/env bash

while true; do
echo "Enter path of video file you wish to change."
read vid
echo "How much offset do you want? | Examples 6.1, -6.2"
read oset

#Seperate the audio video here.
ffmpeg -i $vid -vn -c:a copy outaud.aac &&
ffmpeg -i $vid -an -c:v copy outvid.mp4 &&

#Put them back together with offset here..
ffmpeg -i outvid.mp4 -itsoffset $oset -i outaud.aac -c copy -bsf:a aac_adtstoasc Output.mp4 &&

#If good quit, if not repeat.
read -p "Play the video Output.mp4, is it good y or n  " yn
	case $yn in
		[Yy]* ) rm outaud.aac; rm outvid.mp4; exit;;
		[Nn]* ) echo "Try again"; rm Output.mp4 ;;
	esac
done

Make that script executable

Code:

chmod u+x offset.sh

Then execute it.

Code:

./offset.sh

Answer the prompts.

If you can't get enough offset that way then make one offset positive and the other negative. 6 seconds is a lot.
Change line 17 to

Code:

ffmpeg -itsoffset -4 outvid.mp4 -itsoffset $oset -i outaud.aac -c copy -bsf:a aac_adtstoasc Output.mp4 &&

Don't say that you can't do it. Dive in. That script doesn't affect your original file.

Pearlseattle · 09-29-2014, 06:38 PM

If you don't try at least teckk's example you'll be permanently banned on a planetary level from executing anything on a console and additionally you'll get extra "Are you sure?" and "Are you really sure?" prompts when executing any GUI command e.g. paste&delete&save&undo.