NTSC-PAL-NTSC (25-23.976+pulldown) and audio sync problem - related?

[ecc]

I took an NTSC DVD of a film that had been converted from PAL and used rePal to get rid of the ghosting and other conversion artifacts which results in a framerate of 24.975. Normally, following Fulcilives guide, I'd then use DGPulldown to properly apply pulldown to 29.970 (custom framerate 24.975 to 29.97 rather than 25 to 29.97 that you would do when starting with a PAL video). In this case, since I wanted to convert it to 23.976, I added assumefps(23.976) to the avisynth script. Six hours later (on the fast encode setting), I ended up with a NTSC 23.976 video. I converted the audio from 25 to 23.976 with BeLight. The resulting ac3 was 1:40:36 while the original was around 97 min.

The first problem occurred when I realized that the m2v now ran almost two hours. I scanned it with DGIndex and found that for some reason after the feature had ended at around 100 minutes, the encoder had tagged on some additional footage from elsewhere in the feature, some of it speeded up. This is strange since the file length was consistent with the ac3 when I loaded it into HCencoderGUI so I guess it happened during one of the two passes.

Stupidly, I just chopped this footage out using DGIndex and wound up with a video file running 1:40:30.89. When I muxed the two files, I found that the audio drifted out of sync after about ten minutes with the audio running slower. I've heard about audio drift during conversions but I'd like to know if my problem is the result of the mismatching file lengths or the conversion from 29.970 to 24.975 to 23.976 and how to solve it. Would cutting out the last 6.89 seconds of the audio file or somehow adding 6.89 seconds at the end of the video cause it to go back into sync?

I wouldn't know how to do either. The only sound editing programs I have (Kristal, Audacity, Wavepad) work with wav files. Can avisynth be used to trim ac3 files and what would one plug it into to output the file (Aften? BeSweet?)? Or can 6.89 seconds of blank video be added to an m2v file with avisynth without several hours of reencoding or outputting a 20+ GB avi file that I have no space for?

EDIT: Turns out I still have the longer m2v file. I opened it in VirtualDub-MPEG2 but the nearest I could get to 1:40:30.89 was 1:40:30.900. I can't simply cut it in DGIndex like I did before because there is no display of the timing when not in preview mode.

[manono]

Hi-

I converted the audio from 25 to 23.976 with BeLight.

That was a mistake, as the "base" framerate on the DVD is 24.975fps. You knew that already since that's what you got using RePAL, so I'm not sure why you switched to using 25fps. I don't know if the out-of-synch can be accounted for by that simple mistake or not. As for the rest, I don't understand much of what you said and have no idea in what other ways you may have screwed up the encoding.

However, I've done probably 200 or so RePAL'd conversions to progressive NTSC DVDs and never had a synch problem. But then I've never messed with the audio either. If redoing the audio for 24.975->23.976fps doesn't fix it, why don't you try keeping it at 24.975fps as you usually do, apply DGPulldown for 24.975->29.97fps, use the untouched original audio and see how it comes out?

[ecc]

I converted the audio (demuxed before converting the video) from 25 to 23.976 because that's what other guides suggested. I wanted to convert the video to 23.976 because its one where I find the PAL speedup noticeable in the audio (especially the film's score). So, I should set BeSweet for 24.975 to 23.976 instead?

On a side note, why do legit DVD companies do such cheap PAL-NTSC conversions when better results can usually be achieved with free software?

[manono]

I converted the audio (demuxed before converting the video) from 25 to 23.976 because that's what other guides suggested.

Use your head now. They were most likely talking about a PAL2NTSC conversion. That's not what you have. You are starting with an NTSC DVD made from a PAL master. After running it through RePAL, you have a framerate of 24.975fps. So, logically, after then adding AssumeFPS(23.976) to the script, you want to convert the audio from 24.975->23.976fps.

So, I should set BeSweet for 24.975 to 23.976 instead?

Yes, but BeSweet may not do it, not sure.

On a side note, why do legit DVD companies do such cheap PAL-NTSC conversions when better results can usually be achieved with free software?

Because we can do things in software that they can't do in hardware. However, one thing they can do is encode for hard telecined 24.975->29.97fps. That is, it'll be interlaced but not blended, and the results will be much better. To prepare a proper NTSC master costs money - lots of money. I've read reports of $20,000 or so. If it's a DVD that's not expected to sell a lot of copies, why not just use the already existing PAL master for the NTSC DVD? Who cares if it looks like crap and the audio is pitched a semitone higher?

On a side note of my own, the Criterion Collection is releasing Berlin Alexanderplatz in a 7 DVD set this week:

http://former.imdb.com/title/tt0080196/

It was filmed for German television at 25fps. Criterion has slowed it to 23.976fps for NTSC DVD, and instead of a 4% PAL speedup, there's a 4% NTSC slowdown. And Criterion claims there was no other way to do it, outside of the things you see in your RePAL'd DVDs, all that field-blending:

http://www.criterion.com/blog/2007_09_01_archive.html#1663497146515801199

Of course we know better. There's a raging controversy going on about it now.

[Alex_ander]

You addicted yourself to getting it out of sync by differently (1000/1001) changing video (24.975/23.976) and audio (25/23.976). If anything else was OK, then you have two choices:
1)if you kept original audio:
- load the video stream into DGPulldown and type 24.975 for input and 29.97 for output (custom mode).
2)if you don't have it anymore and want to use new audio:
- 23.952024 for input and 29.97 for output (this will slow down video by 24.975/25 factor)

P.S. A bit late with my suggestions

[ecc]

Do I have to get the audio again from the disc or can I do a framerate conversion from the already converted ac3? I'm not sure what I would put in there 23976 to ...? It would probably be simpler to rip the audio again rather than try to do the math.

[Alex_ander]

Better to rip the audio again to avoid double compression, then use 24.975=> 29.97 on your existing video encoding, this keeps original duration.

[ecc]

then use 24.975=> 29.97 on your existing video encoding, this keeps original duration.

The video has already been encoded to 23.976 and had 3:2 pulldown applied to that with DGPulldown. The reason was that I wanted to change the duration to the pre-PAL speedup framerate.

I'll rip the audio again and see what runtime I get with 24.975 to 23.976 with BeSweet.

[Alex_ander]

The video has already been encoded to 23.976 and had 3:2 pulldown applied to that with DGPulldown. The reason was that I wanted to change the duration to the pre-PAL speedup framerate.

This doesn't matter, including flagging. By assuming 23.976 before encoding you slowed down the video stream. If you type 24.975 as input, DGPulldown will assume it back and restore original length and make it synched with the old audio again along with flagging.
I understand you want to restore pre-PAL duration, but does BeSweet really work with 24.975?

[ecc]

This doesn't matter, including flagging. By assuming 23.976 before encoding you slowed down the video stream. If you type 24.975 as input, DGPulldown will assume it back and restore original length and make it synched with the old audio again along with flagging.

By old audio, do you mean the PAL-speed audio? If so, that's not what I want to do.

[Alex_ander]

By old audio, do you mean the PAL-speed audio? If so, that's not what I want to do.

Yes, I understand now (as added above) that you want the duration of the oldest, pre-PAL version. Then it's better to process audio.

[ecc]

Thanks manono and alex_ander for your help. I ripped the audio again and converted it from 24975 to 23976 and it is now completely in sync (I scanned through the video and checked). I'll have to remember that when I attempt it again with another title.

[ecc]

Another issue: are there any subtitle editing programs that allow one to type in a custom input framerate? I converted another film from NTSC 29.97 to PAL 24.975 (well, not really PAL) to NTSC 23.976 with 3:2 pulldown, this one with subtitles. The image looks great, the audio matches up but I stupidly loaded the subtitles into Subtitles Workshop and simply change the framerate to 23,976 so there is a bit of lag in the subtitles though I have not checked to see if it grows progressively out of sync like the audio but if not then a small lag in subs is not as damaging as in audio sync but I'd like to find a solution to this (also I realized that the framerate is also responsible for the chapter timing as I once again just took the chapter times from the disc and converted them to 24 with a calculator).

[manono]

Another issue: are there any subtitle editing programs that allow one to type in a custom input framerate?

The VobSub Cutter utility that's included with VobSub can adjust the framerate. You give it the intial and final framerates and it does the rest. It requires IDX/SUB format subtitle input.

I usually use SubStation Alpha for this, though. It requires SSA format subtitle input. It doesn't change by framerate, but by percentage (24.975/23.976=104.1666%). Or you can load an 8-bit mono WAV file version of the audio along with the subs, fill in the times of the first and last subs (based on the final audio) and it'll line them up properly. I'm sure there are other ways as well.

[Midzuki]

are there any subtitle editing programs that allow one to type in a custom input framerate?

Subtitle Workshop.

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