AV sync issue: Clarification and advice for DVD backup

[TopHat]

Hello,
I am just now starting to backup my DVD collection to my computer and I had a quick question regarding MakeMKV reports on AV sync issue.

In short, about 4 months ago I backed up ~50 DVDs using MakeMKV v1.9.5. Of these 50 discs, only twice did I receive any AV sync issue reported in the log. After a few month break I updated to MakeMKV 1.9.9 and am now continuing the backup processes. Only now, I am getting an AV sync report (usually only one per disc) with pretty much every disc I try. Some examples:

Example 1:
AV synchronization issues were found in file '/Users//MKV/title00.mkv' (title #1)
AV sync issue in stream 1,2,3,4 at 0:59:01.037 with duration of 18.5ms : encountered overlapping frame, audio skew is +18.5ms
1 titles saved

Example 2:
AV synchronization issues were found in file '/Users/MKV/title00.mkv' (title #1)
AV sync issue in stream 1,2,3 at 1:01:55.168 with duration of 43.5ms : audio gap - 1.359 missing frame(s)
1 titles saved

I have tried ripping using two different optical drives, and both drives report the same AV sync issue with the exact same timestamp, so I am pretty confident that this is not hardware related. I am also running Mac 10.9 if that is relevant.



I guess my questions are twofold.

1) Has there been some change with MakeMKV regarding AV sync issues? Perhaps the new version of MakeMKV has some kind of bug regarding AV sync issues over older versions? Or perhaps it is much better at detecting/fixing AV sync issues now? Or perhaps this is purely coincidence that I now receive an AV sync issue with pretty much every rip?

2) I have tried searching for this, and am still confused. What exactly does MakeMKV mean when it reports a sync issue and how can I check if I still have a good rip?


Thank you for your time and help! I am a newbie, but I am trying to put the effort into learning the process!

[Woodstock]

The biggest change, which actually took place before 1.9.x if I remember correctly, was whether the sync messages were displayed by default or not. Old, default was to suppress them, new, default is to display.

The sync messages are when MakeMKV tries to match up the time stamps in the video track with the time stamps in the audio tracks. With seamless branching and other general mayhem, there can be small gaps or overlaps, usually at chapter boundaries.

Sometimes they are large... someone posted a message on a forum for another program where the time differences were in the several minute range, rather than fractions of a second. I think that one had 15 minutes of blank video added in to make things match.

[TopHat]

Woodstock,

Thank you for your response!

Yes, whether the display sync messages was checked in the preferences was one of the first things I thought of...although I definitely remember going through the preferences and choosing to display sync messages even in the first ~50 discs I ripped (1.9.5). I also noticed that the sync issue almost always occurs right around the 1 hr mark. Perhaps it is related to changing between layers on the DVD?

So I take it that sync issues are a common and unavoidable thing for DVD rips? My question then is how often does MakeMKV try to match the time stamps? Specifically, I am wondering, how to determine if my rip is acceptable. Should I check the video just before the time stamp noted for the sync issue? Or does the time stamp for the sync issue indicate where the audio and video is most in sync as it has been realigned (in other words should I check the video for errors at times farthest away from the sync issue time stamp - as the synchronization will be progressively worse)?

Other than paying attention to the duration of the noted sync issue (ms vs minutes) are there any other indications of what kind of sync issues might be a cause for concern (overlapping frame, vs missing frame, etc.)?

Sorry for all the questions!

TopHat

[TopHat]

I just tried some rip comparisons between MakeMKV 1.9.7 and MakeMKV 1.9.9 (version 1.9.5 is no longer available on the index of old downloads page and I am not sure where else to find it), and I get the same AV sync issue reported in the same location. So perhaps the lack of AV sync issues in my previous rip attempts was more down to plain luck with the discs I was ripping before, rather than being any changes in the MakeMKV software.

I am still a little fuzzy on how to check if I have a good rip when I do get a sync issue reported though or where the video is most likely to be out of sync in relation to the time stamp MakeMKV reports when detecting a sync issue.

I have also been trying to read up on DVD authoring in general and it is not clear to me how frequent are the timestamps syncing audio and video on a DVD (I assume MakeMKV checks the timestamps whenever they are available). For example, I don't understand when MakeMKV notices an AV sync issue, how much of the video is affected (just a few frames vs a whole chapter or cell vs the whole film).

[Woodstock]

The sync issues will be the same no matter what version rips the disk. I do know that debug logging makes you see more of them in the display window. Did you recently switch to debug logging?

[preserve]

Question about this topic. So with debug mode on, there are a lot (sometimes dozens) of audio sync issues reported. Such as encountered overlapping frame audio skew is +, and frame dropped to reduce audio skew.

(I'm assuming when it says overlapping frame and frame dropped, it's talking about audio "frames"?)

Are DVDs and Blu-rays really so badly authored?

I'm trying to understand the root issue of why all this frame dropping is necessary.