PAL <-> NTSC video conversion?

[John Nelson]

Hi,

Is there anyone here who could post a simple explanation of how material that was originally shot on video in PAL or NTSC is converted to the other standard?

Adding/removing scan lines is simple enough, but I don't get how they can convert between 25fps and 30fps without making the converted video look jumpy or uneven.

The discussion on the R1 and R2 Fawlty Towers discs got me thinking...


Thanks,

-- J.

[dave pattern]

Hiya

As far as I know, it's not unusal for cinemas to just run the film at their usual speed - e.g. a US 24fps film would get shown in the UK at 25fps and would therefore run that little bit quicker and the sound would be pitched slightly higher :)

DVD players that can convert NTSC to PAL50 usually use a technique that I think is called "pulldown" that effectively repeats a frame or two every second to keep the image in sync with the audio track. That's why you get people complaining about jerky playback - some people notice it, others don't.

Some DVD players can also do a NTSC to PAL60 conversion, which I think just involves changing the colour encoding from NTSC to PAL. This relies on you having a PAL TV set that can handle 30 fps instead of 25fps, but does mean that you get smooth playback.

I did used to know how the conversion works for NTSC (e.g. turning 24fps into 60Hz), but I've forgotten! I seem to remember it involves lots of interlacing tho...

[GarethR]

As far as I know, it's not unusal for cinemas to just run the film at their usual speed - e.g. a US 24fps film would get shown in the UK at 25fps...

Er - I trust the smiley on your original post indicated that you knew cinemas don't run 24fps movies at 25fps in the UK!

[dave pattern]

...not all films, but I know that it's a technique that is sometimes used if the only print a UK cinema can source is a US one ...or at least that's what the projectionist at Pictureville in Bradford told me a couple of years back - so I'm gonna blame him if I get shot down in flames. He also told me about the reel change markers that they put onto the film (that black round splodge that appears for a few frames every 20 minutes of so at the top right of the frame), so I think he's fairly trustworthy... but then again!

Apparently the speed increase isn't that noticable... plus if it's a naff film, then you'd be glad that it finishes qucker than watching it in the US :p

Anyway, I seem to remember that this technique isn't viable for DVD players because the audio stream can't be sped up as it would involve resampling it in real time.

[John Nelson]

I understand the issues involved in transferring 24fps films to PAL or NTSC... what I don't understand is how PAL video material (eg. the studio-based parts of Fawlty Towers) is converted into NTSC.

Leaving aside the question of scan lines (ie. how to downconvert 625 to 525), how do you take 5 frames every 1/5th of a second, and make them into 6 frames? It must involve some complex sampling/interpolation...

-- J.

[Oasis]

OK,

To try and clear a few misconceptions up!

Film in cinemas is always 24fps - always.

Film converted to Video for European release is sped up to 25fps

Film converted to Video for US release has additional repeat fields inserted , but is not sped up - this is 3:2 or 'inverse telecine'

50Hz Video to 60Hz video or vice versa is a different and difficult subject!

There are numerous methods used, field dropping/insertion, Linear, Motion Adaptive, Motion Compenstated etc...

This is an area that my employers have made a business from for the last 27 years!, Have a look at the following link for a proper description for Standards Conversion;

http://www.snellwilcox.com/internet/reference/pdfs/estandard.pdf

I hope this is of interest!

Richard Ansell
Snell & Wilcox

Hampshire, UK

[John Nelson]

Outstanding!

Must admit that most of it is over my head, but it confirms what I thought... that native PAL material needs a lot of processing to get it into NTSC.

I have the R1 French Connection box-set. One of the extras on it is a BBC documentary by Mark Kermode on the making of the film. This must have been made in PAL originally - the NTSC version on the disc looks fine, until you study it really carefully. Then you notice a bit of blurring on anything moving in the frame, and the whole thing looks a little soft compared to a native PAL picture.

I think that, where DVD transfers of TV shows are concerned, it's better to buy from the 'native' region.

-- John

[Mark.Anderson]

Having just spent the last ten minutes investigating a problem on a S&W Fame Sync card I'm not sure if believe anything Oasis or Snell & Wilcox say. ;)

[Oasis]

Mark,

As you've discovered getting synchronised with FAME is never easy!

Seriously though, If there is a problem that your local contacts can't help with (Which I hope there won't be - Quinto are good people), feel free to contact me & I'll put you in direct contact with the people that can help.

Richard Ansell
Snell & Wilcox

richard.ansell@snellwilcox.com

[Lambchop]

My computer capture card can capture NTSC, but my brother's DVD player won't play NTSC DVD's, so I want to record the NTSC output from my DVD player and convert it to couple of PAL VCD's. Does anyone have any idea of the best way to do this? I use TMpegEnc to convert to MPEG usually, but when converting to different formats is there a better way to do it so that you don't get that stuttery picture??
Perhaps I should start a new thread in console and computing for this...?