Audio and video get out of sync when authoring MPEG2 to DVD

[palex]

I thought this was not possible but I have an MPEG2 that plays OK (audio and video are in sync) on my computer but once authored to a DVD format with TMPGAuthor started having a huge delay (up to 7 seconds) between audio and video which starts with no delay at the beginning and ends with 7 seconds at the end of the movie (1.5 hour)

This MPEG2 was created from WMV.

Can anyone explain me please why this happens? Thanks

[manono]

Hi-

Can anyone explain me please why this happens?

Maybe. What's the framerate of the MPEG (or of the original WMV)? One way to explain it would be if the framerate of the MPEG was either 24fps or 30fps, and the DVD framerate becomes 29.97fps. Some quick figuring says there's a 5.5 second difference between 29.97fps and 30fps after 90 minutes. Other than possible framerate differences, I haven't a clue.

[palex]

Manono,

it is quite likely that the framerate of the original WMV was not 29.97. I converted it to the MPEG2 with 29.97 and when I play the MPEG2 the audio/video are in sync. The question is why the VOBs that TMPGAuthor creates from this MPEG2 have audio/video no longer in sync?

[manono]

it is quite likely that the framerate of the original WMV was not 29.97. I converted it to the MPEG2 with 29.97 and when I play the MPEG2 the audio/video are in sync.

The WMV isn't 29.97fps, the MPEG-2 is 29.97fps, yet they're both in synch? So the audio was stretched? By whom or what or how? MPGs can be any old framerate. Only vobs have to output a specific framerate. What I was suggesting was that the MPEG and the Vob have 2 different framerates, or 2 different lengths. Unless you know for sure just what the framerates are, or know exactly how to determine the video lengths, then we can't determine if differing framerates is the problem.

By the way, perhaps the best way to compare the lengths of the MPG and the VOBs is to make a D2V of each using DGIndex, stick each D2V into its own .avs file using MPEG2Source, and then open each in VDub(Mod) to compare the lengths. If my hunch is correct, then one will be longer than the other, which will then explain the asynch audio of the VOBs.

[palex]

Manono,

I converted WMV to MPEG2 with WinAVI. The target I chose was MPEG2, NTSC and I specified 29.97 fps. Are you saying that the MPEG2 I generated did not actually have 29.97 fps? How come that when I was looking at this file (using some Info utility) I saw 29.97 fps, NTSC, etc, all the information was the same as on all other 'good' MPEG2 files?

Or you saying that MPEG2s frame rate does not affect audio sync as opposed to VOBs???

I'm just don't understand this part - how come that MPEG2 is OK but VOB from it not!

[aedipuss]

lots of avis have a 25fps rate. your original probably did. during conversion to 29.97 the time codes can get out of line. i don't know if dvdauthor has the tool but what you can use in dvdlab pro after importing and demuxing on the .m2v file is it's tool re-write gop timecode which adjusts the video only file to 29.97fps internally, to match it back up with the audio during the re-mux.

[palex]

Aedipuss, Manono, please explain me how come that MPEG2 did not have the sync problem while playing but VOB from it did?? Isn't it that MPEG2 should also have the same problem since it was improperly converted from WMV?

[aedipuss]

it occurs in the authoring process when the file is demuxed and remuxed. i see it most of the time in pal to ntsc conversions.

[manono]

He's only got approximately a 7 second asynch by the end of the video, aedipuss, so it can't be from a PAL2NTSC conversion, or vice-versa, where the difference would be in minutes over a 90 minute video.

palex, I was only saying that one explanation could be differing framerates, 30fps .vs 29.97fps. The difference over 90 minutes would give you the slight asynch of which you speak. Another possible explanation might be an audio conversion somewhere along the line, if the audio for the MPEG wasn't DVD compliant. (AC3, WAV, or MP2) and had to be converted. Like I say, it would really help if you could accurately figure the lengths of both the MPEG and the VOBs, to see if that's where the problem is. You haven't even said yet just what the WMV framerate was.

[aedipuss]

i know it doesn't make mathmatical sense, but i've had pal to ntsc conversions turn out as little as 4 seconds off. rewriting the gop timecode has fixed 99% of the async issues for me.

[manono]

OK, I stand corrected. Never seen that one myself, although I've seen you mention it several times. Maybe that will fix palex's problem.

[palex]

Manono, I don't know the frame rate in WMV, my utility shows about 6 fps which can't be true. I tried converting WMV directly to VOB with WinAVI and it didn't have async problems but it was converted to a PAL DVD. How can I check the length of MPEG and VOB?

"...if the audio for the MPEG wasn't DVD compliant..." - the audio was embedded into MPEG2 during WMV to MPEG2 conversion, shouldn't it be DVD compliant then?

Aedipuss, you said that out-of-sync occures in authoring process during de-mux /mux. But I still don't understand why MPEG was OK, why it was not out of sync as well? Authoring creates VOB which internally is the same as MPEG2, no conversion to another format happes there, isn't it? So the length of VOB should be the same as MPEG2 and the audio should be the same as in original VOB. Besides, de-mux splits video and audio and mux joins them back, no conversions occures in these 2 steps so if the original MPEG2 had video and oudio the same length then re-muxed VOB should have them the same length, isn't it?

[manono]

Hi-

shouldn't it be DVD compliant then?

To tell you the trutn, I don't know. Never made an MPG in my life. I don't think they have to be DVD compliant, though, since they aren't VOBs. You could open it in GSpot and it'll say the kind of audio. It may even tell you the length of the video.

How can I check the length of MPEG and VOB?

I mentioned one guaranteed way earlier, and the way I do it when I really need to know. But if you don't know any AviSynth, this isn't the time to begin, I don't guess. If you'd like me to walk you through the process (not hard), just let me know. Maybe other people know of some accurate ways to tell.

[Abond]

How can I check the length of MPEG and VOB?

Open it in VDubMod. File->File information