Audio for PAL to NTSC

[Machine514]

I am converting a PAL VCD (25fps) to NTSC VCD (29.97fps). I got the video to convert properly, but I am having problems with the audio. It sounds like it is sped up (which it probably is to meet the conversion specs, i.e the math of the situation).

I used TMPGEnc to split the files. I converted the video with TMPGEnc, no problem. I then used BeSweet to convert the PAL audio to NTSC. What setting should I be using? (Please post from experience, I check the forum guides and there is nothing for PAL to NTSC.) Just for the heck of it I multiplexed the files and played the VCD on the computer. Everything seemed to be in sync.

The settings I used are as follows...

Under BeSweet...
Presets PAL to NTSC 25fps to 29.97fps
downconvert sample rate
use MPA decoder
convert to MP2

Under SSRC...
perform 2 pass conversion

2Lame...
encode to stereo

Please help!

-Machine

[Lythium]

Don't convert the audio fps. Change to 48k sample rate and remux the audio with the video.

[Machine514]

I figured it out and made a VCD compliant video. The audio must be "stretched" (to the length of the converted video) in Cool Edit 2000 keeping the pitch constant and have cool edit determine the other specs (I forget exactly what it is but it is next to the pitch constant option). I converted, saved, converted again with BeSweet and then muxed and works real good. Made a VCD, played it in my DVD player and all A/V is in sync.

I hope it was not luck and works consistantly. I am in the process of now doing a SVCD. Will post my results later!

-Machine

[adam]

No, you have to change the speed of the audio to match the newly encoded video.

Machine, I've often wondered why BeSweet has both PAL->NTSC and PAL->NTSCfilm options. The playback speed of NTSC and NTSCfilm is identical. When film is transfered to NTSC, rather than speed up the playback to increase the fps, new frames are simply added every second so the # of seconds remains the same, and thus the playback speed is also the same.

I know it sounds strange, but to properly time shift audio from PAL 25fps to NTSC 29.9fps you should actually be slowing the audio down, so if your audio sounds sped up then BeSweet is doing something wrong, or this particular settting serves some special purpose which I don't understand.

My suggestion is twofold. First off, convert your audio to NTSCfilm instead of NTSC in BeSweet. It should sync fine with your current 29.97fps video and it should sound about the same as the source. Second, I would strongly recommend encodign your video to 23.976fps rather than to 29.97fps. The latter is a very inefficient way to convert to NTSC and it is much more difficult to do well. Unless you used Avisynth or TMPGenc's 3:2 pulldown filter, you probably did it incorrectly.

The easiest way to convert the video from 25fps to 23.976fps is to just load appropriate NTSCfilm template and then enable the "do not framerate conversion" filter on the advanced tab.

[Machine514]

Is 23.976fps a standard NTSC frame rate?

I did one conversion to 29.97fps. It seemed fine or more important it was to my satisfaction. If 23.976 is a standard framerate for NTSC maybe I will try that. I just though that 29.97fps was the standard. Although when I converted the NTSC video, it was a few seconds shorter than the PAL video.

I am working on an SVCD conversion right now. I am going from 25fps to 29.97fps. We'll see what happens.

Another question...as a rule of thumb, should all frame rate conversion go from a higher frame rate (say 25fps PAL) to a lower framerate (23.976)? Also what happens to the video when changing the frame rates?

-Machine

[adam]

29.97fps is the only supported playback speed for NTSC, but 23.976fps is supported internally in most digital video formats. What this means is that the video is stored at 23.976fps and converted to 29.97fps during playback. For VCDs, 23.976fps is supported directly, you can just encode at this fps and leave it. For SVCDs and DVDs you must include a 3:2 (or 2:3 same difference) pulldown flag. This is what instructs the dvd player to do the conversion.

Ok, here is regional format conversion in a nutshell. Film is shot at 24fps, and as you already know, PAL runs at 25fps and NTSC runs at 29.97fps. To convert to PAL, you simply speed the video and audio up by 4%. You have the exact same frames, they are just playing at a slightly faster speed.

This won't work with NTSC because the framerate difference is too great, so you must physically increase the number of frames, rather than just increase their playback speed. But if you were to just duplicate frames, then it would be too noticable. So what happens is each frame is interlaced. Basically, it is broken up into two fields with each field representing exactly half of that frame's information. Then fields are repeated in a specific pattern, with 2:3 being the most common pattern. This increases the actual number of frames by about 20%, but since its being done in such small increments and in a specific pattern, you don't notice it. Since you have only increased the # of frames and not their playback speed, the length of the film has not changed (well you have to account for drop frame but this is minimal.) This is why your PAL clip is 4% shorter in length than the NTSC version, it was sped up.

Now, the BIG problem with NTSC is that you have 20% more frames once your done with the conversion and these frames use up your bitrate. It is for this reason that it is much more efficient and higher quality to encode at 23.976fps and let the hardware player do the conversion to NTSC on the fly. You save 20% more bitrate and this grants you a quality increase of about 15%.

So there is no rule of thumb saying you must only convert from higher to lower or vice versa, you simply convert to what you need. But, if you are converting for digital output than there is never any reason to need 29.976fps, since 23.976fps is much easier to convert to (you'd actually have to convert to 23.976fps before you could even convert to 29.97fps) and it is much higher quality.

[Machine514]

WOW! Very good explanation. But I still have some questions.

Can TMPGEnc encode to 23.976fps?

Do all DVD players convert 23.976fps during playback?

Will I have a problem when using such programs as (S)VCD2DVD to convert to DVD cmpliant videos?

What and where do I define the 2:3 or 3:2 pulldown flag?

-Machine

[adam]

1) Yes, TMPGenc can encode to 23.976fps. It has ntscfilm templates for both VCD and SVCD, and of course you could make one for DVD, and you can set the output fps to 23.976fps on the video tab under settings.

2) Well, all NTSC DVD players certainly can. Nearly every single commercial NTSC DVD is actually encoded at 23.976fps and telecined to 29.97fps during playback. This is something that you should emulate on all of your NTSC digital conversions. As long as you remember to always include the pulldown flag when encoding in mpeg2, yes all dvd players will properly do the conversion if they support that format, ie: SVCD.

3) I've never used (S)VCD2DVD so I can't say, but if I were manually converting SVCD to DVD, than it certainly wouldn't be a problem. The only real difference between a SVCD compliant mpg and a DVD compliant mpg is the resolution and potentially the GOP structure, neither of which have anything to do with the framerate.

4) If you look on the video tab in TMPGenc under Encode mode you can select 3:2 pulldown while playback. Also, you can run any m2v video stream through the program pulldown.exe. (best to grab the gui.) Both of these methods will add a pulldown flag to the stream. Its just a bit of information which the DVD will parse before playing the video.

[Machine514]

WOW! Once again, very good. I will have to digest this, try it and then get back to you (probably with questions).

Would an autmoated version of this process be beneficial to the whole PAL to NTSC process? Is anyone working on this?

Thanks again!

-Machine

[Cornucopia]

I agree with what adam was saying IF the source is 24fps Film.

If the source originated from a Home Camera, or TV news, etc. You can't do 23.976 and have it look decent. It F**KS with the temporal resolution. If you're converting from a PAL source, that just adds to the problem.
I'm not saying don't do it, I'm saying MAKE SURE your source actually was 24fps film.

Here's what I'd do:

PAL (film-based) video (25fps) --> slow down 4% --> convert to temp AVI @ 24fps --> Encode w/ Pulldown flag --> new NTSC M2v @ 23.976internal/29.97playback

PAL audio --> slow down 4% ("uncompensated" time compression) --> convert to temp wave --> (if needed, SRC 44.1kHz-->48kHz) --> new PCM file, or Encode to AC3/Mp2

Then remux and/or reauthor.

If you're actually going from video-based PAL to video-based NTSC, I'd either do a 5:6 pulldown or a speedup with associated audio. (Depends on content)

Hope that didn't confuse the situation.
Scott

[adam]

I agree with what adam was saying IF the source is 24fps Film.

I was talking about converting from another format to NTSC, ie: Film to NTSC or PAL to NTSC, meaning the film either originated as PAL (yup there are camera's that record in 25fps) or FILM at one point or another. After re-reading my post, this was definitely not clear though so thanks for clarifying.

What I really mean is that converting to ntscfilm is always preferred if its possible. If your source is PAL and desired output is NTSC, then you should always convert to ntscfilm and let the player do a soft telecine to NTSC.

@Machine: Its a fairly automatic process as is, in my opinion. The majority of the manual work would be in regards to the audio, but BeSweet has built in regional format coversion options so it takes care of all that for you. As for video, you can just use the same AVS script everytime or you can just set your encoder to the desired fps and resolution, something which you would always have to do anyways. If using TMPGenc, just make sure and enable the "do not framerate conversion" filter. That's really all there is to it.

[Machine514]

Just to clarify, use the "do not framerate conversion" and 3:2 pulldown?

-Machine

[adam]

Correct, but use the 3:2 pulldown while playback option under the encode mode setting on the video tab NOT the 3:2 pulldown filter on the advanced tab...huge difference.

The author of TMPGenc really should rename the filter on the advanced tab to 3:2 telecine rather than pulldown. Its very confusing as is.

[Machine514]

Great, I will look again at it tonight.

One question though. Is there a program that will analyze an audio or video file and tell me the stats?

For instance...framerate, NTSC, PAL, MPG1, MPG2, kbps, files size, length, etc etc. I think something like this would make my life a lot easier!

-Machine

[adam]

You can download Telco's BitrateViewer from a link in the tools section to your left. It will tell you most of that information. As far as framerate, when dealing with NTSC material you cannot go by what is reported by decoders, ie: media player, etc... The whole point of NTSCfilm is that it is stored interally at 23.976fps but played back at 29.97fps, so whether or not the fps is reported as NTSCfilm or NTSC, depends entirely on whether or not the decoder parses the pulldown flags.

So, if you need to determine whether your source is NTSCfilm or NTSC, you have to use dvd2avi. Preview it and if it reports Film in the statistics than it is NTSCfilm, and if it reports NTSC or a low percentage Film, ie: 60% than it is NTSC.

[Sugar]

So, if I understand you correctly Adam, this should also work to convert a DV avi PAL file (edited in my case with Premiere) and encode it into NTSC MPEG (I want to eventually put it onto a DVD).

Can you first change the DV avi film frame rate from 25fps to 23.976fps and reduce the avi film time length to the original time length (this should accelerate the video by 4%) or is it better to let TMPGEnc deal with that ?


I am wondering wether the resulting quality would be better if dealt by Premiere or by TMPEGEnc ?

[Machine514]

Adam...

I got the audio and video to sync perfectly. This is what I did.

Converted video from original using TMPEnc with the NTSC film template.

Used BeSweet to convert audio with the option PAL to NTSC (25fps to 23.976fps).

Audio and video are in sync at the beginning and then at the end the video seems to disappear. I went back and checked my converted video file and it cuts off some of the end. It has the right length but the video is just a black screen.

Any ideas?

-Machine

[Machine514]

That's the damn 3rd video file that cuts off the video at the end. What the heck is going on here. Someone please help!

-Machine

[Mont]

Machine, what were the exact settings you put your audio on in BeSweet. I've been following these posts trying to use them, and when I put my audio in BeSweet and transcode, it justs sits there. And are you changing to Mp2 or Ac3.

[Machine514]

I figured it all out and will post my method.

-Machine