The most lossless way to edit an AVI & export when audio is out of sync?

[Neil-Betamax]

What would be a good way to re-align the audio of my uncompressed AVI captures?

I'd like to do this before I de-interlace and then compress to MP4 as this process is working well for me.

Most of my captures turn out well & in sync, but a fair few have audio sync issues - Betamax for example, so do a lot of DV tapes. I'd like to be able to manually align the audio from the uncompressed AVI whilst retaining as much quality as I can before I export it, de-interlace & compress.

My current process is this:

* VHS S-Video output through Panasonic DMR EX79.
* RCA audio out from VHS into the DMR's Audio in (through a mixer to get audio levels right)
* S-Video & RCA audio out the DMR > into Black Magic Shuttle.
* Black Magic Shuttle into Thinkpad (i7 8th Gen) via USB 3.0.

* Captured with Black Magic Media Express - 625i50 PAL 8bit AVI YUV.
* De-interlaced with AviSynth & the compressed with FFMPEG to MP4.

The audio sync issue is from the master, uncompressed AVI.

I used to edit the audio in Davinci Resolve before exporting to MP4. Now I'm doing it this way using AviSynth & FFMPEG which thanks to some of you on here, I'm getting great results but since it bypasses the need for a video editor, I'm unable to correct the audio sync if it occurs.

any ideas would be great!

Thanks everyone

[Alwyn]

Here's what I do to correct sync in AVISynth:

v=LSMASHVideoSource("File.mp4")
a=LSMASHAudioSource("File.mp4").Normalize(0.98) #Normalise is optional

AudioDub(v,a)
delayaudio(.3) #  Positive is delay, negative is advance in seconds-this example is delay by 0.3 of a second

[themaster1]

I guess the most easy way is to use a NLE, work on the sync and export the audio only . Finally in Vdub you can mux the original video + new audio.

you can also use the audiodelay line in avisynth

avisource(myvideo.avi)
assumetff()
delayaudio(0.5) #0 in milliseconds

[poisondeathray]

Is it a constant delay issue , or a progressively worsening sync issue ?

[videoAI]

try clever FFmpeg-GUI

[Aro]

If You're looking for an easy way to do it, Avidemux has that option (Audio->Choose Track-> Filters->Adjust in milliseconds).

[themaster1]

If You're looking for an easy way to do it, Avidemux has that option (Audio->Choose Track-> Filters->Adjust in milliseconds).

i second that, forgot about good ol' avidemux

[Neil-Betamax]

Hey everyone, thank you very much for all your input. As with these things, time is often the biggest factor, I'm a little short of it at present & I guess I need to dedicate myself to this again when I can contemplate everything suggested here. So I appreciate your suggestions 100%, I just need a month or two till I can get back to this as I'm in the process of moving house / setting up a new business etc too.

Once I have dedicated focus on this again, I'll take this in. It's mostly the Betamax recordings which need capturing again, or compressing using a few of the techniques you've mentioned.

I were hoping there would be some kind of software available to allow manual adjustment of an audio timeline using a lossless AVI, which could then export the AVI as lossless on the second export - although I think this is wishful thinking, as I understand each time you export an AVI it's not possible to retain its initial quality in comparison to the master. There will always be some form of degredation as I'm aware. It was worth a shout though, I'll try out that code in AviSynth Alwyn, you've always been really helpful on here & I appreciate that very much PAL

Its been trial & error for many years, so I'm familiar as to when the audio starts to become out of sync on each tape, when I go back to re-capture and try again. So far I can only see it possible by manually draggin the audio in the timeline when it goes out, from betamax captures its not consistent, it tends to happen between blank parts in the tape. So I find myself matching audio with moments of sudden impact, like a door closing, a glass reaching the table or a "B" consinent when re-syncing audio with a vocal part of the video.