PAL to NTSC audio speedup

[K4S3RYN]

I'm converting concert footage from pal to ntsc 29.970. Done the vid with CCE fine and transcoded the audio thru Besweet, but the speedup makes it sound ridiculous.. is there a solution? The lengths match..

[manono]

Hi-

Which lengths match? The 29.97fps video and the 29.97fps audio match? Then the video speedup should be noticeably ridiculous as well.

You slow it down when converting from PAL to NTSC. So, make the video 23.976fps (AssumeFPS(23.976) in an .avs script is one way) and run pulldown afterwards to get it to output 29.97fps. And slow the audio to 23.976fps, and then it'll sound fine.

[K4S3RYN]

Gotcha.. cheers. I had run it through a script but had it on assumefps 29.976. Will try this and see, thanks

[K4S3RYN]

Ok done that. The video looks fine but the audio is noticeably slower, or lower in pitch though not ridiculously so. Is this just an occupational hazzard of the conversion to ntsc ?

[FOO]

It's only 4%. The important question is whether or not it's in sync
with the video.

[manono]

Hi-

Yes, if you play them one after the other, then the difference is obvious. However, there's at least a fair chance that the NTSC version is the original and correct one. You didn't say what the source or group was, but often to create the PAL DVD, the original 24fps footage is sped up to 25fps. Although there are such things as 25fps cameras, most film is created at 24fps. And although when converting to 25fps it's possible to pitch correct the audio, my understanding is that it isn't usually done. If that's the case, then you're just restoring it to the way it sounded originally, and your new 23.976fps version is the more accurate of the two.

[K4S3RYN]

I see.. that all makes sense. Thanks for the info. I'm letting dvdlab do the pulldown when i import them. Are these actually playing back at 29.970 on the dvd player then? How come i haven't needed to speed the audio up to that rate.. ?

[FOO]

If 1 second of audio matches 24 frames, and it's played at
24 fps it all matches and takes 1 second. If you convert
24 to 30 by adding frames , and play it at 30 fps , it still
takes 1 second and the audio still matches.

[manono]

Hi-

Are these actually playing back at 29.970 on the dvd player then? How come i haven't needed to speed the audio up to that rate.. ?

Although you'll be storing it at 23.976fps on the DVD, the pulldown process will set flags (some programming) so that it outputs 29.97fps. This is the famous 3/2 pulldown. Upon output, it will create new fields to fulfill the NTSC requirements of 29.97fps (actually 59.94 fields per second). Whether 23.976fps or telecined 29.97fps, the length is still the same, and the audio is still in synch. Lemme see if I can find my favorite link that explains the process...

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

A little ways down you'll come to the section entitled, "NTSC Telecine (Transfer of 24fps Film to 60Hz NTSC TV)".

The reason you don't want to speed the audio to 29.97fps is because it isn't 29.97fps. It's 23.976fps. Now, if it were created as pure interlace, as many concert NTSC DVDs are, then it would originally be 29.97fps, and the audio would be at that framerate also. But this is converted from a PAL 25fps DVD (whose source may or may not have been originally 24fps), and making it 23.976fps is closer to the PAL 25fps, so both the video and audio speeds will look and sound more natural after conversion.

Whenever possible, you'll want to store your movies at 23.976 progressive on your DVDs. They'll have 20% fewer frames when compared to telecined 29.97fps, and the available bits will be distributed among fewer frames, resulting in a better quality DVD.

[dphirschler]

Most likely it is PAL video, not film. In that case, you need to approach converting to NTSC completely differently as your source will be 25i.

I suggest using the sample avisynth script found under ConvertFPS in the documentation. The only thing you will need to worry about is field order. If you get that right, then your conversion will be perfect. If you get it wrong, then you will have stuttering.


Darryl

[K4S3RYN]

I seee.. clever stuff.. thanks again all. The source is as u say 25i [from a PAL DVB] .. using the assumeFPS method seems to have worked great. No synch loss or visible interlace artefacts. Its an American tv series from the 80's.. so i guess woulda been recorded in film originally anyway eh.. and therefore not too bad with the 4% diff. What do they do to convert 29.970 to PAL then.. strip frames? I didn't know that abuot NTSC concert dvd's.. cheers all

[dphirschler]

I thought it was concert footage. If if was an American TV series from the 80s, it could be video or film. Who knows? You gotta know your source before you can do it right.


Darryl

[K4S3RYN]

Ah.. well it looks fine. I've got ntsc output on the dvd player/tv and aren't reading any probs, so i guess it's ok. Thanks all for the tips..