[FFmpeg-user] Extracted Audio not in Sync with Video

[Josh]

Sorry for top posting again, forgot about that!

So this worked. I added "[1]rubberband=tempo=.99991[aud];" to the filters 
and now the audio and video all sync properly.

But this created a new problem. Now the audio has some slight distortion. 
It almost sounds like an mp3 that doesn't have a high enough bitrate. It's 
very faint, and most people probably wouldn't notice it, but I can 
definitely hear it. Are there other ways so change the tempo that won't 
distort the sound?

Josh

On Wed, 1 Nov 2023, Torsten Kaiser wrote:

> (top posted since the whole thing is top posted)
>
> That is what I do for adapting audio length to the video track
>
> In preparation I calculate the durations in seconds for VIDEO.mp4 and 
> AUDIO.mp3 separately. Must be different files to get the length difference.
>
> Korn Script Snippet
>
> # ADSS is audio length in seconds (n.nn)
>
> # VDSS is video length in seconds (n.nn)
>
> typeset -F5 TEMPO=$(( $ADSS / $VDSS ))  # calculates the correction factor 
> for audio length, five digits precision
>
> #then I apply the rubberband filter to the AUDIO.mp3
>
> ffmpeg -y -i .AUDIO.mp3 -af rubberband=tempo=$TEMPO audio-corrected.mp3
>
> #Merging corrected audio and video
>
> ffmpeg -y -i .VIDEO.mp4 -i audio-corrected.mp3 TARGET.mp4
>
> #Note: rubberband has two nice options: tempo and pitch. Tempo makes the 
> marching band play the same tune while running a marathon.
>
> #Pitch leaves the speed as it is while the cantor either sings with the 
> whales or attracts all bats in the forest. Default is 1 for same tempo and/or 
> same pitch.
>
>
> On 31.10.23 15:34, Joshua Grauman wrote:
>>  I tried this and it doesn't help. The audio and video are still not in
>>  sync, even when you don't use the fade-out...
>>
>>  Josh
>>
>>  On Tue, 31 Oct 2023, 凯迪软件（咨询、售后） via ffmpeg-user wrote:
>>
>>>  ffmpeg -y -i "v1-ed.mp4" -i "a1-ed.wav" -filter_complex "[1]anull[aud];
>>>  [0]fade=t=out:st=6673.87:n=24[out]" -strict experimental -shortest -map
>>>  0:v:0 -map 1:a:0 "lecture.mp4"
>>> 
>>> 
>>>
>>>  ??????????????????????????????????????????
>>>  You can try using this command to see if it can solve your problem.
>>>
>>>  The translation in English is: "Try canceling the fade-in and fade-out
>>>  effect you added."
>>> 
>>>
>>>  china kaidi
>>> 
>>> 
>>> 
>>>
>>>  ------------------ Original ------------------
>>>  From: "FFmpeg user questions" <jnfo-d at grauman.com>;
>>>  Date: Tue, Oct 31, 2023 07:31 AM
>>>  To: "ffmpeg-user"<ffmpeg-user at ffmpeg.org>;
>>>
>>>  Subject: [FFmpeg-user] Extracted Audio not in Sync with Video
>>> 
>>> 
>>>
>>>  Hi all,
>>>
>>>  My use case is that I want to extract audio from a mp4, edit the audio,
>>>  and then put the audio and the video back together. It works fine, but
>>>  over the course of the two hour video, the audio gets out of sync with
>>>  the
>>>  video and falls behind it (visibly, so you can see the mouth and sound
>>>  aren't in sync).
>>>
>>>  I extract the audio with a command like this:
>>>  ffmpeg -y -i "v1-ed.mp4" -vn "a1.wav"
>>>
>>>  I edit a1.wav with audacity to create a1-ed.wav.
>>>
>>>  And then combine audio and video with a command like this:
>>>  ffmpeg -y -i "v1-ed.mp4" -i "a1-ed.wav" -filter_complex "[1]anull[aud];
>>>  [0]fade=t=out:st=6673.87:n=24[out]" -strict experimental -shortest -map
>>>  [out] -map [aud] "lecture.mp4"
>>>
>>>  Is there any easy way to make sure the audio stays sync'd through this
>>>  process?
>>>
>>>  Thanks,
>>>
>>>  Josh
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