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

[Joshua Grauman]

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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