[Denatonium]

I used dvgrab to ingest my old tapes, and ffmpeg and avisynth/QTGMC to de-interface and encode files for easy viewing (though I keep the original .dv files).

The biggest issue I ran into was that while the audio and video were properly synced up in the original .dv file (due to it being an interleaved format), when I re-encoded the videos, the audio and video would drift out of sync as the video went on.

I was able to fix the sync issues by using dvgrab to split the original dv file into a bunch of 3 minute chunks. I then wrote a script to extract the audio track from each chunk, pad the end of the audio with milliseconds of silence to the exact length of the video track, combine the padded audio tracks, encodes the combined track, and muxes the fixed audio track with the encoded video. This worked really well; the silence padding is imperceptible, but the audio and video are still in sync - even after 2 hours.

A final point that needs making is that doing anything with dv files in ffmpeg (even -c:v copy) destroys the SMPTE timecodes embedded in the original file, making it much harder to split by scene.

[CountHackulus]

Just because I've dealt with this exact issue in the past, it may have been a 30fps vs 29.97fps issue. For me the audio was a fixed length, but the frame rate was SLIGHTLY too fast. The problem can manifest as either too slow or too fast depending on which side is expecting 30fps vs 29.97fps.

[Denatonium]

I think it was just clock drift on the camcorder during the initial recording, as I'm pretty sure I tried adjusting the frequency of the audio track to make it the same duration as the video track, and the A/V sync was still wrong.

I'm so glad the audio and video tracks are stored interleaved, as it made my solution possible, and the results I got were great. By splitting the interleaved video into small enough chunks, padding the audio, and cutting it exactly to video length, the padding was practically imperceptible.

The only issue I ran into was that ffmpeg can't cut audio with any real precision. I eventually figured out that I could dump the audio track to a headerless PCM file, calculate the exact byte offsets for my cut points, and cut them with perfect precision using the head and tail commands from GNU coreutils. This was perfect because I was able to use the cat command to combine all of the padded audio chunks into a single raw PCM file, which I then made an AAC encode of with ffmpeg to mux with my original encoded video track.

[Melatonic]

This is very likely it

[Melatonic]

Transcode to another format first that keeps the timecode?

[Denatonium]

Ffmpeg's dvvideo implantation is unfortunately just broken and mangles timecodes, even if just doing a stream copy from dvvideo to dvvideo without any re-encoding.

Fortunately, dvgrab does allow you to take the original .dv file and generate a .srt subtitle track with time stamps that you can mux into your encoded files.