Number of problems with DVDa and AC3 (5.1)

blink3times wrote on 11/8/2008, 8:29 AM
I never used DVDa before and therefore never recognized the number of AC3 problems it has... is it me or other too? Quite a few times now I have done these tests and they are reproducible each time so I'm inclined to believe it's DVDa but none the less....

I export a M2V and a AC3 (for test purposes I created 2 AC3 files... a studio version and a pro version) file from Vegas. I know that both AC3 files are good and contain all 6 tracks because I have imported them to adobe audition and physically looked at them. They are the same as what I exported from Vegas. Both these AC3 files work fine in other burner programs.

I then import (for the first test) the M2V and the studio AC3 file and burn a Blu Ray disk (as a M2TS). I then re import that M2TS from the disk and bring it back into Vegas (and adobe audition)

The second test is performed the same way only with the Pro AC3 file.

What I am finding is this:
DVDa wants to recompress the audio in the studio version and when it does it screws it up completely. Only the front left and right tracks show some what normal activity except the right track is slightly louder than the left. All other tracks are there but flat lined (0db).

With the pro version, there is no recompressing of the audio and 5 of the 6 tracks come out in good shape... all but the LFE track which again there but flat lined.

I have no problems with Vegas's AC3 file and other programs.... it's just DVDa. Is any body else experiencing anything similar?

ADDED: I'm using DVDa 5a, but the same happens in DVDa 5.0

Comments

blink3times wrote on 11/8/2008, 9:47 AM
Something else interesting...

I just noticed that when i reimport the M2TS files from the finished disk back into Vegas and have a look at the clip properties:

Video: 00:05:29.029, 29.970 fps interlaced, 1440x1080x12, MPEG-2

Audio one is clearly marked "STEREO DOWNMIX"

ForumAdmin wrote on 11/8/2008, 9:47 PM
Blu-ray requires an AC-3 audio stream that is AC-3 Pro. Anything else will be recompressed to AC-3 Pro if you selected AC-3 for your audio type. This is why your AC-3 Studio audio was recompressed (yes, there is a difference).

The AC-3 5.1 audio stream in MPEG-2 can be decoded as either stereo (which is a downmix) or as full 5.1. Vegas will load the audio as 5.1 if your current project audio is set to 5.1, or it loads it as a stereo downmix if your project is stereo. These are displayed as two streams in the clip properties as you have noted, but they actually use the same audio stream data from the file. The difference is in how they are decoded.
blink3times wrote on 11/9/2008, 3:40 AM
Thanks for the explanation ForumAdmin. It's quite a help in understanding what's happening. Although I should point out that it is not very well documented that the Pro encoder MUST be used.

However I still don't understand why the LFE track is coming through flat lined (0db) even though the pro encoder is being used. Not that the LFE track is of an real importance for our purposes, but DVDa does advertise that it supports Dolby Digital 5.one
blink3times wrote on 11/9/2008, 4:35 AM
As indicated by the attached photo (link works sometimes and sometimes not!??!!?!):

The rightside:
The rendered AC3 file exported from Vegas was imported into Adobe Audition 3 which in turn broke the AC3 into individual WAV files and is displaying as such. You will note that all 6 tracks are there and in good order.


The left side:
The above AC3 file (and a M2V) was burned to Blu Ray disk using DVDa. All settings were for AC3 (5.1). The resulting M2TS file was reimported from the burned disk back into Vegas. As you can see the LFE track is there, but flat lined.

http://forums.pinnaclesys.com/forums/svsappsdb2/forums/storage/143/170003/Compare.jpg

Use this link if the other one doesn't work:

http://forums.pinnaclesys.com/forums/storage/143/170003/Compare.jpg
blink3times wrote on 11/9/2008, 12:58 PM
I stand corrected. This "lost" LFE track issue is NOT a DVDa bug. It is a Vegas bug.

The final M2TS file from above that was dragged back into vegas APPEARS to have lost its LFE track, but in fact the LFE track IS there. If I demux the AC3 from the resulting M2TS file then drag that AC3 into Adobe Audition the LFE track is there and clearly visible. It is Vegas that is losing the LFE track.

It is the EXACT same problem Stuart was having a short time ago:

http://www.sonycreativesoftware.com/forums/ShowMessage.asp?ForumID=4&MessageID=617035
TheHappyFriar wrote on 11/9/2008, 1:32 PM
so you burn a 5.1 AC3 to a BD disk & only 5.0 tracks are actually there? You played it & nothing shows up from the sub? What happens if you burn the same thing to DVD? i've done 5.1 with DVDA 4 & 4.5 no problem, never tried BD though. Don't use DVDA 5 either.
blink3times wrote on 11/9/2008, 2:12 PM
"so you burn a 5.1 AC3 to a BD disk & only 5.0 tracks are actually there? "

No... I THOUGHT it wasn't there. It actually turned out to be a bit of Vegas trickery. If I re-import the M2TS off the disk back into Vegas, all 6 audio tracks show up on the time line. But the LFE track is empty. It just shows a flat line. So I ASSUMED Vegas was telling the truth and there was no LFE track.

But if i bring that SAME AC3 sound track into Adobe Audition and look at the peaks. the LFE track is in fact there... and it even plays. So the problem is Vegas.... some how it is losing the LFE track on import.

It's taken me all bloody day and about 100 test strips to figure this out! It's the EXACT same problem that Stuart was having with his AC3 import to Vegas in the above mentioned thread.
TheHappyFriar wrote on 11/9/2008, 5:18 PM
Just tested, same results with 5.1 from DVD Mpeg's too.
blink3times wrote on 11/9/2008, 9:32 PM
File a bug report on it. the more that file the better the chance of this getting corrected faster.
TheHappyFriar wrote on 11/10/2008, 10:56 AM
i never tried importing a multi-channel vob because vegas doesn't import straight ac3.

filed.

plus, when I went to file... saw this.

so it may be related to that.