Out of synch after converting the 44.1Khz Audio to 48 Khz

[Eric Beaudoin]

Hi all,

For over a month, I've been trying to convert my VCD Mpeg (Video = 29.970 fps, 352*240 (4:3), MPG1, Audio = 224 Kbps, 44100 Hz, 2 channels, 0x51 = Mpeg-1 audio Layer 2 [0xc0]) to mpeg that can be authored on a DVD.

I think think I've read pretty much every forum threads and guides on the subject (those on this site and quite a few from other sites) and I'm out of ideas. It's pretty much always the same method: you de-mux the mpeg, you convert the audio to 48Khz mp2 or ac3 and you re-mux. I tried TMPG, Bsweet, ffmpeg, and more recently MPEG-VCR. I also tried letting TMPG Author, (S)VCD2DVDMPG and Nero do the whole thing completely. None of these have work so far.

My problem is that I can never get the sound to be synchronized properly. The resulting mpeg starts OK but at some point, the sound get off-sync by 2, 3 and sometimes 4 seconds. After many experimentations, I realised that the sound doesn't get off-synch gradualy but by steps. For example, everything is fine for 5-10 minutes and then the sound gets 2 seconds off-synch instantly.

MPEG-VCR has a function to fix audio and GOP problems in MPEG files. I've used that to see if it would help. When I scan a file for error with MPEG-VCR, everything is fine for say 5-10% of the file and then audio PST errors start pilling up by the thousands. If I use the repair function from MPEG-VCR, I end up with an 44.1 Khz audio file that is off-sync the exact same way my 48 Khz converted audio files are.

When I use the MPEG Scan from VCDEASY, only one error is reported: aps' pts seems out of order (actual pts 539.605356, last seen pts 539.638722) -- ignoring this aps.

So, did anyone faced this problem before? Am I on the right track thinking that the "aps' pts seems out of order" is the cause of my headaches? Does anyone know how to fix an "aps' pts seems out of order" error? (I would like to find a way that doesn't require for me you recode the whole MPEG since that would defeat the purpose of just converting the sound to save time and preserve as mush video quality as I can).

The standard trick of de-mux/re-mux in TMPG that gets rid of the unaligned packets didn't remove the pts out of order.

Any help would be greatly appreciate, TIA

[rcb]

Eric - from your post

>After many experimentations, I realised that the sound doesn't get off-synch gradualy but by steps. For example, everything is fine for 5-10 minutes and then the sound gets 2 seconds off-synch instantly<

That sounds more like dropped video frames. I don't have a magic bullet answer/fix for you, but possibly your vcd vid file had some padding that got lost during the conversion.. ?

[ChrissyBoy]

Have a look at my ramblings on the subject:

Audio/Video out of Sync. Why? Well...

[Eric Beaudoin]

Thanks guys,

Recoding the files did solve the problem. No more PTS out of order. I'm a bit sad that recoding is the only way out of this. It's quite long. I was thinking, since I'm recoding anyway, is there a way to convert directly to MPEG1 with 48 Khz audio in one convert?

Also, anybody knows if mush quality is lost with this extra video convertion?

[Eric Beaudoin]

It appears I was wrong. Recoding remobed the PTS error but the sound is no longer sync in the resulting mpeg.

I'm all screwed up again.

[aklendathu]

Hi, Eric.

It seems we have the same problem. I'm also recoding MPEG-1 VCD clips to DVD format and after recoding the audio gets out of sync. I suspect the problem lies in the original file - I open it in VirtualDUB and by looking at Video->FrameRate it gives 29.97 fps for video and 30.01 fps for audio.

I have been able to solve the problem by first converting the VCD file to
AVI (XviD) and then encoding that file to MPEG-2. However, this is time-consuming and I am also looking for a better way.

Cheers,

Pedro.

[Eric Beaudoin]

Hi Pedro, thanks for the tips. I'll try VirtualDUB and see if I have the same problem. However, I was not trying to make a DVD format, I was just trying to re-encode the MPEG-1 using the standard VideoCD (NTFS) template as suggested in one of the messages linked by ChrissyBoy. I wanted a MPEG-1 files without any PTS error.

I'll let you know what VirtualDUB says.

[cooljoe666]

Converting from 44000 top 48000 or vice versa does not affect the audio sync. Only the frame rate and errors cause the problem and maybe a few other least likely problems. If the audio is jumping off at a particular point then it is definitely a bad frame. Keep in mind that VDUB may not read the error. When this happens I use videofixer and divfix to do a check for errors. Use both one at a time to do a check and see if errors popup and make a note of the bad frames. Then go back into VDUB and goto each bad frame and delete it. I don't use mask because that sucks. You may be able to just let videofixer try and fix the file. I have had it do miracles for some really crappy files.

:P

[Eric Beaudoin]

Hi cooljoe666, yea, I'm pretty sure it's a missing/bad frame problem. The tools you suggested however do not work with mpeg files. I used the mpeg analyser from VCDEasy to find the "pts seems out of order" but unfortunately, I don't know how to match the PTS number to a frame. Any idea?

BTW, VirtualDUB didn't find any error whatsoever with the file but the playback within it get off-synch at some point. I'll have to play around to find where but I'm not sure I'll be able to pin-point a frame that way.

Pedro, there is indead more audio frame than video frame but that's normal. I've checked with a mpeg file that doesn't give me any error or sync problem and I have the same ratio. Still, I might try to convert to AVI and converting again to mpeg just to see what will happen.

Best

[aklendathu]

Eric,

Thanks for the info. Since my last post I discovered that I can reencode the MPEG-1 to MPEG-2 without loss of audio sync with Nero Vision Express 2, and without the need for an intermediate AVI step. If you're just looking for MPEG-1 to MPEG-1 fixing there's a couple other tools you may try: VCDGear also has a MPEG-1 fixing tool (although it didn't work very well for me), VCDCut 4.04 and IFilmEdit 1.4 (the best in my experience).

Cheers,

Pedro.

[Eric Beaudoin]

Thanks for the info Pedro.

I tried VCDGear and no matter what options I select, the resulting "fixed" MPEG is always worse then the original. By worse I mean that MPEG-VCR finds way more errors in it then the original, that VCDEasy (MPegTools 1.6.1 actually) is not even able to analyse it because of a header error and if I do a de-mux/re-mux with TMPG without converting anything, I get a MPEG that won't play properly. Anyone who knows VCDGear is welcome to shed some light here.

I downloaded VCDCut but didn't find any repair function in it.

I'm not able to find IFilmEdit anywhere since the product is no longer sold.

This is beginning to feel like an hopeless situation.

[kyemeng]

Not sure if I can be of any help, but I will try!
Have you tried to extract the audio using Goldwave?

[Eric Beaudoin]

Any suggestion is good . I wil try GoldWave if I can. Is there a demo version available anywhere? There doesn't seam to be one on their site.