Reverse field dominance – two fields forward, one field back

[Michael Pfost]

One addition – when converting the 25fps 720×486 video to 25fps 720×576, I did use Compressor’s Crop function to take off the top 2 and bottom 2 lines (as they had video not needing to be shown).

Did this create an issue?

[Andrew Rendell]

I suspect you’re going to have to do the conversion again. I don’t understand why your going from 29.94fps to 23.98fps before going to 25fps. Every change in frame rate adds errors, so why do it twice unless it’s absolutely necessary? Do you actually need to have a 23.98fps version (and if you do, why not do it as a separate thing)? Regarding the specific field dominance problem I guess that in going through so many steps, it’s got mixed up somewhere along the line, so I’d check the last one (the one you deliver) then check the previous step, then the one before that, etc, until you find where it went wrong.

Another thing – if you’ve got a lot of this to do, I’d suggest getting some proper conversion software (as a stand alone or a plug-in) to do the job as it’ll save a lot of time and technical headaches in the long run. Ask around or search the forum for advice on which to get, I’m sure it’s come up before…

[Andrew Rendell]

Re: One addition – when converting the 25fps 720×486 video to 25fps 720×576, I did use Compressor’s Crop function to take off the top 2 and bottom 2 lines (as they had video not needing to be shown).

Did this create an issue?

Hard to say, but probably not in regard to the field dominance thing.

[Michael Pfost]

Hi – thanks for the response. I was using the inverse telecine workflow so that my resulting PAL video would not have any blended frames. It was basically a 4.1% speed-up from the original 24fps version.

It plays back beautifully, but I’m not sure how to analyze the video and see where the issues might be.

Is there a program that will analyze a clip and report field dominance and frame order issues?

[Andrew Rendell]

Well, if you’ve got 24 frames in a second and you make them into 25 frames you are either creating blended frames somewhere or its repeating one, which would be noticeable. I don’t really worry about blended frames per se myself, but rather whether it looks good or not (which I know isn’t a particularly helpful thing to say at this point, sorry).

I’m not sure what to suggest for software as I use a facility (or occasionally a broadcaster’s mastering suite) when it comes time to deliver stuff, so I have access to their scopes, etc, which is the expensive stuff. I’ve seen a couple of things, but I don’t know them thoroughly so I’m not comfortable making a recommendation. Anyone?????

It has worked for me to do a technical test involving a facility to establish settings, then I’ve gone away to do the processing on my own kit (that was a job where I delivered some items for broadcast as IMX files over ftp).

[Jeremy Garchow]

Did you try just making a PAL version from your NTSC version? Set everything to best in Compressor and let it cook.

[Michael Pfost]

I’ve done the frame blending and optical motion rendering with Compressor, but these interpolate the frames.

I was trying to go about it the correct method of speeding up 23.98 fps video to 25 fps. This is what they expect in PAL markets.

[Jeremy Garchow]

[Michael Pfost] “I was trying to go about it the correct method of speeding up 23.98 fps video to 25 fps. This is what they expect in PAL markets.”

Mmm, I’ll bite my tongue on that one. Hardware NTSC to PAL converters don’t convert everything to 24p first. I would use those for best quality (send it out to a transfer house).

But since I am sure no one will pay for any of that, I’d try Compressor, everything set to best.

[Jon Bagge]

1. Convert NTSC DigiBeta to NTSC ProRes 4:2:2 file
2. Reverse Interlace NTSC ProRes file into NTSC ProRes 23.98 fps (Progressive) — using Compressor

By ‘reverse interlace’ do you mean remove pulldown? I’m not an expert on these american issues, but surely that will only work if your material is originally shot in 23.98p? If you remove pulldown on footage shot 29.97i you’ll end up with some frames containing 2 different fields. When you then speed up to 25i (I assume you’re speeding up here?) you’ll end up with some fields being different on the same frame and some identical. That won’t be acceptable as you’ve found out.

You should be using a method that interpolates 29.97i to 25i. I sincerely doubt compressor will be able to do that at a quality acceptable for broadcast. You’re going to need some more specialised plug-ins (and some serious rendering time), or much better – use a proper hardware conversion box made for doing this.
These are rather expensive, so you’re probably better off sending this all off to a post facility that can do it all for you.

————–
http://www.jonbagge.net
Jon Bagge – Editor – London, UK
Avid – FCP – After Effects

[Michael Pfost]

I’m starting to think that this may be a configuration issue with Episode Pro (using it to create the final MXF file).

I know this is the wrong forum, but in Episode Pro I have to create Op1a compliant files with the IMX-50 codec. There is a frame order setting as well as a frame-rate setting (with some advanced settings). Perhaps I need to re-examine these.