AC3 and DVD Lab - when to mux?

[housepig]

okay, here's the deal...

I'm hoping mkelley or willy_annand will jump in on this one...

I found that the reason I have distorted / really really loud audio in many of my discs to date is because I was using mp2 audio, which isn't totally compliant with NTSC.

So I've started to encode to an m2v stream and a pcm audio stream. then I take the pcm audio and run it through BeSweet, which gives me the AC3 stream.

I can import these both into DVD Lab, no problem. The problem is that on some of the discs, I lose audio sync.

Now here's my question - I've been importing elementary streams into DVD Lab. If I mux the m2v and ac3 into an mpeg-2 file with TMPG, check to make sure the audio is in sync, and import that mpeg, no demux, into DVD Lab, should the audio remain in sync?

Or is my sync issue related to ac3 in general? I do not have any problems with sync when I use mp2 audio - just excessive volume & distortion.

so should I (and can I) mux first, or should I let DVD Lab mux? Or is it a quirk between ac3 and DVD Lab?

any input appreciated. thanks all.

[FOO]

You have not discovered anything.
NTSC is a TELEVISION VIDEO standard which has nothing to
do with Mpeg audio.

Your video is NOT distorted becase it's MP2. It is distorted
because you screwed up somewhere.

Why don't you just try what you propose instead of asking other
people what-if questions ?

[racer-x]

What bitrate are your ac3s?

I've done the same as you with the same apps and have'nt had any sync problems. Although the longest video clip was 35 min. But it played in sinc the full length. I've never premuxed the video and audio.

The reason I ask the bitrate, is because I had some errors when I encoded to 384 kbps ac3 with Besweet. But when I use 224 kbps, I have perfect sound.

[andkiich]

What's up with the hostility?

[FulciLives]

Once you have your M2V and AC-3 I would try the following:

1.) Multiplex into an MPEG file and play it back using a software DVD player on the computer to double check if it is in synch ... if it is then you know the problem probably is with DVDLab. If it is out-of-synch then you know it is something else related to how you are doing things.

2.) Perhaps even better than point 1 is to try a different DVD authoring app assuming you have another one you can try. If you don't own another authoring app then perhaps you can download one that has a set-period demo mode. Again this is to see if another program either stays in synch or not ... in other words eliminate DVDLab from the equation in order to isolate the problem (it either is DVDLab or it isn't).

Also please note that usually 2.0 AC-3 audio is either 192kbps, 224kbps or 256kbps. Going higher than 256kbps with a 2.0 AC-3 might cause problems so if you are using a higher bitrate that might be another area to check (including the settings you are using in BeSweet).

I've never used DVDLab so I am sorry that I cannot offer more help.
I should point out though that it is not uncommon on these forums to hear people having synch issues when using DVDLab so knowing that it could be that the program has some odd bug that only shows up on certain systems or with certain settings etc.

One more point about the audio. Why are you encoding the audio to LPCM and only THEN converting to AC-3. It seems to be that it would be wiser to take the audio in whatever format you first have and convert it directly to AC-3

In other words ... maybe the problem is using the LPCM audio as a source for the AC-3. Perhaps BeSwet doesn't like that type of source. It seems a bit odd and I would imagine very few have actually done it this way since most would convert to AC-3 to begin with (omitting the LPCM part) or just be happy with either MP2 or LPCM as is.

Again, as a test ... make a DVD with DVDLab using LPCM audio without converting it to AC-3 and see if it is in synch. Also maybe try converting the original audio to AC-3 directly and authoring that with DVDLab.

I'm sure the answer is in here somewhere but the more I think about it ... I'm thinking it might be the way you are converting the audio ... OR the way DVDLab handles your processed audio.

- John "FulciLives" Coleman


- John "FulciLives" Coleman

[spectroelectro]

Muxing won't help because most DVD authoring programs demux into elementary streams during authoring even if they dont' tell you they do.
Trying to fly in one AC-3 demuxed from one MPG into an m2v demuxed from another MPG has never worked for me. Even tryign to demux a VOB into its elementary streams and then transcode the AC-3 into mp2 for VCD has never worked me -- I always wind up losing sync.
Si suspect AC-3 has internal frame markers of some kind. A mismatch twixt the number of frames in AC-3 and the m2v, even by one, seems to throw things off.
Try this:
Take your original avi load into VirutalBub, then select video...frame rate and select audio video duration match. then select direct stream copy and resave the new avi -- then see if it's in sync.
You might have to go backwards from m2v + AC3 to AVI and then forward to mux'd MPG to make this work.
RULE OF THUMB: compressed digital video streams were not meant to be edited!
I've only been able to fix these kinds of audio sync problems by dumpign everything back into AVI and then re-encoding...but your mileage may vary.

[turk690]

I'm interested to know what housepig used to generate his *.m2v and and PCM (*.wav, I suppose) streams. I've just concluded a similar project, where I transferred "Apartment 0" on LaserDisc to DVD, first capturing to two DV AVI files (one 12G, the other 13GB) with Premiere 6.5. Then, I exported the work area to an *.m2v and a *.wav file with the built-in MPEG encoder, using 4x3 NTSC hi-bitrate from the accelerated presets folder, leaving the quality slider to 21 and ave. bitrate to 6200kbps as they are. Since I used the color saturate & sharpen filters in Premiere encoding took more than 24hrs. The resulting *.wav I converted to *.ac3 with BeSweet, using a 256kb/s bitrate (taking a cue, as racer-x has noted, that with Dolby digital 2.0 streams on commercial DVDs the only bitrates I ever saw were 192, 224, and 256 kb/s). The *.m2v and *.ac3 I gave to DVD-lab (1.22b) where I also created menu selections. After all these the resulting DVD size was about 5.2GB, so I opened the file set with DVDShrink3beta, and reduced it to 4.7GB. After burning with Nero 5.5.10.42 and testing audio and video throughout the whole DVD these were in perfect sync (on a Sony DSNVP530 DVD player).
I'm puzzled about the distorted mp2. Either a very low bitrate was used (?) or the original *.wav was in itself not generated optimally (clipping?) The only bone about ac3 is that the volume is low, but I found out this has to do with the levels set by AC3filter in conjunction with WMP9.0 when playing back through that; BeSweet does NOT reduce levels, because converting back to *.wav and examining the actual waveform in CoolEdit shows it has the original levels.
I only discovered BeSweet recently and b4 this created some NTSC DVDs with *.mp2 audio, which worked perfectly with the above DVD player (proving that NTSC/*.mp2 is largely a non-issue with recent DVD players). It could be that since *.mp2, for some reason, when played through WMP or PowerDVD is much louder than an *.ac3 created by BeSweet from the same material then having set the volume at some level that can distort the former.

[housepig]

You have not discovered anything.
NTSC is a TELEVISION VIDEO standard which has nothing to
do with Mpeg audio.

Maybe I wasn't clear - I understand that NTSC is a television video standard. I have also read reports that mp2 audio is more supported on PAL dvd players, and is not universally supported on NTSC - meaning it will play, but it may not decode correctly.

Your video is NOT distorted becase it's MP2. It is distorted
because you screwed up somewhere.

My video isn't distorted at all, it's the audio. The audio is fine on my computer, both in the original .avi files and the converted mpeg files with mp2 audio. When it gets through authoring, it's fine on my computer. When it gets to my dvd player, it's much louder to the point where it starts to distort.

Why don't you just try what you propose instead of asking other
people what-if questions ?

check the time stamp on my post - it was late, I was about to crash out, and I didn't want to stay up for another hour to figure it out. I also specifically said I was hoping that mkelly or willy_annand would jump in, because they know DVD Lab well, and have experienced (and worked around) this issue.

Now that I'm up, I plan on trying it - but I thought that some night owl might have some constructive information. Instead, I get you.

Sorry my question bothered you so much, but if someone pissed in your Wheaties, it wasn't me.

[housepig]

@Racer-X:

What bitrate are your ac3s?

all are 224kbs.

@Fulcilives:

1.) Multiplex into an MPEG file and play it back using a software DVD player on the computer to double check if it is in synch ... if it is then you know the problem probably is with DVDLab. If it is out-of-synch then you know it is something else related to how you are doing things.

did it this morning. the ac3 is in sync if I mux it back with tmpg. Now the problem is that DVD Lab won't accept the muxed file - it can't read the mpeg made from a muxed m2v and ac3, and it can't demux it on import either....

2.) Perhaps even better than point 1 is to try a different DVD authoring app

that's next... I just don't like any of the others available to me as much as I like DVD Lab .... but now it's "process of elimination" time...

One more point about the audio. Why are you encoding the audio to LPCM and only THEN converting to AC-3. It seems to be that it would be wiser to take the audio in whatever format you first have and convert it directly to AC-3

The reason is that I use the Source Range control in TMPG a lot, to set my start and end points to cut heads and tails of the video file. If I go back to the original file and strip the audio, I'd have to try and get it exactly trimmed to those points - a daunting task. If I take it from a TMPG-created PCM stream, I know that it is the correct length.

And I do have a couple files on the docket where I have access to a wav file stripped from the original .avi, so I'll try those later today.

thanks for the input, guys.

[FulciLives]

HOUSEPIG ...

Good luck and let us know how things turn out

- John "FulciLives" Coleman

[FOO]

Sorry Housepig
I guess I need to change my medication

[housepig]

Sorry Housepig
I guess I need to change my medication

no problem, man. it's effin' hot, tempers flare...

and yeah, it probably did look like a stupid question - but like I said, I was hot, I was about to crash, and I was hoping someone could give me some theory by this morning before I went through the process to act on it.

in any case, I've been sidetracked all day, so I probably won't get to act on anything until this evening.... but I did have a good side trip, dumpster diving at Blockbuster... 110 dvd, gamecube & ps2 cases...

[mastersmurfie]

I thought this might be the right place for this post...I use TMPG to demux my mpegs to m2v and mp2...then AC3Machine to create the AC3 sound file...only I get almost exactly the opposite of Housepig: My sound is STILL loud and distorted...even using the "attenuate" (had to look that word up... ) to -5db for the resulting AC3...

only I use DVDLab to "remux", and no sync probs...just TOO LOUD audio...