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Compressor 4: When do I select Reverse Telecine?

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Edwin Street
Compressor 4: When do I select Reverse Telecine?
on Jan 26, 2015 at 6:10:53 am

Is there a chart somewhere that could show me when to use Reverse Telecine and when not to.

For example:
50i to 60i?
30p to 25p
50i to 30p

I've never really understood when to use it? Is it only for when dealing with interlaced footage? Does that mean less people are using it now as we move into a more progressive world?

While we're here could you briefly explain when to use inverse telecine too?

Cheers.


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John Rofrano
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 26, 2015 at 1:40:16 pm

[Edwin Street] "Is there a chart somewhere that could show me when to use Reverse Telecine and when not to."
Telecine is the process of taking 24 fps film and creating additional frames to bring it up to NTSC 29.97 fps for video broadcast. It does this by a process called 2:3 pulldown (sometimes referred to as 3:2 pulldown) which slows the film down by 1/1000 to 23.976 fps and then distributes those cinema frames into interlaced video fields. Reverse telecine is the opposite process of taking 29.97 fps video and converting it back to 23.976 fps by removing 2:3 pulldown and deinterlacing. There are numerous ways to add pull down including 2:3:3:2 which makes editing easier but the concept is the same.

So the chart of when to use reverse telecine would looks something like this:

29.97 fps to 23.976 fps (i.e., 60i to 24p)

That's It! It has nothing to do with 50i to 60i, 30p to 25p, or 50i to 30p. It just takes 60i video and converts it to 24p (obviously deinterlacing 60 fields into 24 progressive frames along the way).
[Edwin Street] "While we're here could you briefly explain when to use inverse telecine too?"
Inverse Telecine (IVTC) and Reverse Telecine are the same thing. Perhaps you mean Telecine and Inverse Telecine? Telecine goes from 24p to 60i and IVTC goes from 60i to 24p. Telecine is also used with other film frame rates (16 fps, 18 fps, 20 fps, etc.) but it is most commonly used with 24 fps.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Shane Ross
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 26, 2015 at 1:40:48 pm

John beat me to the punch!

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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John Rofrano
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 26, 2015 at 9:53:59 pm

lol... barely. Both our posts were on 8:40:16 am. I guess I had a stronger cup of coffee. :-D

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Shane Ross
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 26, 2015 at 1:40:16 pm

[Edwin Street] "50i to 60i?"

No. That's called a Standards Conversion. PAL to NTSC. 25fps to 30fps

[Edwin Street] "30p to 25p"

Nope..again, Standards Conversion. NTSC to PAL. 30fps to 25fps.

[Edwin Street] "50i to 30p"

Another example of Standards Conversion....25fps to 30fps.

[Edwin Street] "I've never really understood when to use it?"

When something was shot 24fps, and telecined onto tape as 30fps (a film term...scanning film) . So you have a 30fps tape with 24fps footage on it...and you want to make it 24fps again. You "reverse telecine" it...pull out the redundant frames and fields (pulldown). the 24 frames are spread out in the fields of a 60i tape...so interlacing is involved.

http://en.wikipedia.org/wiki/Telecine#Reverse_telecine_.28a.k.a._IVTC.2Finv...

[Edwin Street] "Does that mean less people are using it now as we move into a more progressive world?"

No, there are plenty of cameras that still shoot 24fps at 30fps. And some older cameras that are hanging around.

[Edwin Street] "While we're here could you briefly explain when to use inverse telecine too?"

INverse Telecine is just another term for Reverse Telecine.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Edwin Street
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 27, 2015 at 4:40:26 am

Thanks John and Shane for your simultaneous responses. ;) That's cleared things up.

On the topic of standard conversion, how does Compressor 4 do it? I'm converting 30p to 25p. I've read that when we watch American shows here in Australia they are slowed down about 5% to become PAL.

When is this slow down/speed up technique used and does Compressor 4 do it? After a simple test my 5min video came out at exactly the same time from 30p to 25p, so I'm guessing it just dropped some frames to go to 25p, it doesn't seem to slow it down 5%.

Thanks again.


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Shane Ross
Re: Compressor 4: When do I select Reverse Telecine?
on Jan 28, 2015 at 8:53:53 am

Only shows that are shot 23.98 are speed changed to 25fps. And that is done by various needs...the one available to you is Cinema Tools. 30fps to 25fps is done via a terranex or Snell/wilcox...or Compressor (with lesser results)...and the same speed is maintained.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Brandon Don
Re: Compressor 4: When do I select Reverse Telecine?
on Feb 11, 2015 at 6:20:09 pm

Firstly i want to say thanks to everyone contributing to this area of telecine as i'm having a few issues with it myself... Is inverse Telecine basically normal telecine and Reverse Telecine is the only other option?

I am in Canada so we are using NTSC

My issue at hand is that our content is basically all PAL programming and our post house captures our PAL tapes and delivers it to us in either23.98 or on occasion 29.97. I need some clarification on the point of Telecine as we are now delivering our distribution products to Amazon. Here is what i was written by their Video guy after he confirmed they want our programming as un touched as possible. Everything delivered to Amazon we are sending in Pro Res.

As Written by Amazon-
" You can check the header data in a video file really easily with MediaInfo which is a free utility you can find on the internet. If the content is telecined (has 2 combed/interlaced frames every 5 frames) we would prefer the content be inverse-telecined to return the content to a progressive 23.976fps on your end, before delivery."

-Firstly when would i be using a telecine or reverse telecine on such footage or with the facts i put above about our footage would this mean it doesn't require telecine in any way? My guess is the post house is doing a simple frame rate change from the Pal to the 23.98 or 29.97. I also will note that mostly all of our programming is interlaced according to the media info.
-When will i need to use telecine or reverse for such work?
-Since most of the our programming is interlaced whats the best way to make it progressive using MAC applications? Compressor? FCP?
-I believe our post house is no longer using their teranex machine to change our frame rates on our PAL content so i wondered if you could explain why the teraned is better then using a program to do the frame rate conversion


And one other thing in the spirit of using our converted material.

- I have done authoring projects using supplied 23.98 video and had no issues with compressing it in Compressor (to MPEG 2) and then ending the process in DVD Studio Pro. Why did that not need to be converted to NTSC to work as a playable DVD?

Again Thanks so much for your time all.


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John Rofrano
Re: Compressor 4: When do I select Reverse Telecine?
on Feb 12, 2015 at 4:36:22 am
Last Edited By John Rofrano on Feb 12, 2015 at 4:38:45 am

[Brandon Don] "My issue at hand is that our content is basically all PAL programming and our post house captures our PAL tapes and delivers it to us in either23.98 or on occasion 29.97. I need some clarification on the point of Telecine as we are now delivering our distribution products to Amazon."
It sounds like the post house took some of the 25 fps PAL video and slowed it down to 23.976 fps while for others they slowed it down to 23.976 fps and then applied Telecine to bring it up to 29.97 fps. If this is the case, then all of your 29.97 fps footage has Telecine applied and it needs to be removed by applying Reverse Telecine.

Just to be clear:
  • You don't need to do anything to your 23.976 fps footage. Just send it to Amazon as is.
  • All of your 29.97 fps footage needs to have Reverse Telecine applied to bring it back down to 23.976 fps.
You can use Apple Compressor to do this. I only have Apple Compressor 4 so I can't tell you the settings in other versions but you need to:
  1. Select the ProRes 422 template
  2. Under Video Properties change the Frame Rate to 23.976
  3. Under Video Properties change the Field Order to Progressive
  4. Under Quality change the Retiming Quality to Reverse Telecine
This will remove the Telecine from the 29.97 fps footage and bring it back to 23.976 fps and make it progressive. Now you can send these to Amazon.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Brandon Don
Re: Compressor 4: When do I select Reverse Telecine?
on Feb 12, 2015 at 8:05:01 pm

Thanks so much for the answers, much appreciated.

Just a couple things i wanted a bit more of clarity on that im still unsure of. Sorry if i repeat myself but unfortunately im not sure how this footage was put to 29.97 or 23.98. Can't they both just be straightforward frame rate conversion vs. the use of telecine and reverse telecine?

How do i know that the 29.97 fps footage was not a frame rate change from PAL through an application or using a Teranex to the 29.97?

Does it not matter how the footage got to 29.97 and the reverse telecine will work to get it to 23.97 in compressor regardless of how the footage was processed? I thought Amazon would be fine would be fine with 29.97?

I figured most people did conversion in a program to their preferred destination frame rate vs using the Telecine.

Again thanks.


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John Rofrano
Re: Compressor 4: When do I select Reverse Telecine?
on Feb 13, 2015 at 1:27:55 am

[Brandon Don] "Sorry if i repeat myself but unfortunately im not sure how this footage was put to 29.97 or 23.98. Can't they both just be straightforward frame rate conversion vs. the use of telecine and reverse telecine?"
While it's true that you don't know how they were converted unless you ask the person who converted them, it is common to slow 25 fps media down to 23.976 and then telecine it to 29.97. But you're correct. Unless you ask the person who did the conversion, you will never know.
[Brandon Don] "How do i know that the 29.97 fps footage was not a frame rate change from PAL through an application or using a Teranex to the 29.97?"
Teranex will also use telecine to convert from 23.976 to 29.97 so you just don't know. Telecine is an algorithm that both hardware and software programs use for frame rate conversion.
[Brandon Don] "Does it not matter how the footage got to 29.97 and the reverse telecine will work to get it to 23.97 in compressor regardless of how the footage was processed?"
All that matters is that it looks correct. If you use Reverse Telecine and it looks fine then you're done. If it doesn't then try one of the other methods of retiming.
[Brandon Don] "I thought Amazon would be fine would be fine with 29.97?"
I guess they're looking to get the footage as close to it's original format as possible. That gives them the most options to work with.
[Brandon Don] "I figured most people did conversion in a program to their preferred destination frame rate vs using the Telecine."
Telecine is a process not a "thing". It's the way that you convert from 23.976 to 29.97. You can use other algorithms but it's just an algorithm. If someone used telecine to go from 23.976 to 29.97 the proper way to get back to 23.976 is to use the reverse telecine algorithm which will undo the frame rate conversion correctly. I think you are being confused by the fact that there was a piece of hardware called a Telecine but it's all done in software now.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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