Standards Conversion

G Filters for Final Cut Pro: Standards Conversion

Instructions

Installation

Install the filters by copying them to the Final Cut Pro Plugins folder ->

/Library/Application Support/Final Cut Pro System Support/Plugins

These filters have been tested with FCP3 and FCP4 under OS X. I strongly recommend FCP 4.1 for speed and stability while using the Standards Conversion plugins.

Introduction

G Standards Conversion package contains two complex filters that have been designed to convert between the three standards of NTSC video (29.97 frames per second), PAL video (25 frames per second) and 24p (24 frames per second progressive). G Converter deals with the video to video frame rate conversions, and G Film Converter deals with the video to film frame rate conversions. Both plugins will correctly scale the converted clips if necessary.

The PAL and NTSC standards conversion work best with interlaced footage (50i and 60i respectively), although during testing, a 25p PAL video clip was converted to NTSC with excellent results.

Both G Converter and G Film Converter work in a very similar manner. This method of working is necessary to bypass the poor in-built Final Cut Pro / Quicktime frame rate conversion and allow the high quality algorithms to work effectively. Also, if a change of clip resolution (scaling) is needed, the clip on the timeline should be nested to allow the plugin to work correctly. Again, due to limitations in FCP, the plugin must be correctly informed of the Source Pixel size of the video that is to be converted. If you find that there is not a setting for the source media you are using, then please email me at [email protected] for it is an easy task to add in the required sizes.

General Method

The general method of operation is as follows:

PAL to NTSC conversion

1) edit the PAL clip to an NTSC timeline

2) nest the PAL clip to allow the plugin to scale the converted clip correctly

3) apply the G Converter clip to the nest in the NTSC timeline

4) open the nest in the viewer (control click on the nest and select "Open in viewer" or select nest then press return)

5) select the filter tab in the viewer

6) set the correct settings for the desired conversion. In this case, we select Source Pixel size to be 720 x 576 (PAL), lower field order for source (in this case a PAL DV clip) and destination (NTSC DV timeline).

7) if you desire the NTSC output to be de-interlaced, this can be performed in one step by selecting progressive output

8) if you would like to experiment with the conversion algorithm using "Smart De-Interlacing" then this can be selected in the De-Interlace options. The Tolerance control effects the smart de-interlace and it's effects can be seen by selecting "View Smart Mask" in the De-Interlace Options.

9) the original PAL clip that was edited to the NTSC timeline must now be dropped onto the Source Clip image well in the filter. The plugin will use this this video clip for all the image data for the conversion. This is the important step that makes this plugin different from any other, and is vital to it's successful operation.

NTSC to PAL conversion

1) edit the NTSC clip to an PAL timeline

2) nest the NTSC clip to allow the plugin to scale the converted clip. Because the pixel dimensions of NTSC video are smaller than PAL, the clip will appear shrunk down in the timeline canvas viewer. This is normal. The nesting of the clip will allow the plugin to correctly scale it to PAL pixel dimensions.

3) apply the G Converter clip to the nest in the PAL timeline

4) open the nest in the viewer (control click on the nest and select "Open in viewer" or select nest then press return)

5) select the filter tab in the viewer

6) set the correct settings for the desired conversion. In this case, we select Source Pixel size to be 720 x 480 (NTSC), lower field order for source (in this case a NTSC DV clip) and destination (PAL DV timeline).

7) if you desire the PAL output to be de-interlaced, this can be performed in one step by selecting progressive output

9) the original NTSC clip that was edited to the PAL timeline must now be dropped onto the Source Clip image well in the filter. The plugin will use this this video clip for all the image data for the conversion. This is the important step that makes this plugin different from any other, and is vital to it's successful operation.

To help follow the special method of use of this plugin, please watch the enclosed "Standards Conversion Tutorial" movie clip that demonstrates this procedure in operation.

Source Clip - An "image well" where the source PAL or NTSC clip must be dropped

Source Pixel Size - Selects the pixel dimensions for the source PAL or NTSC clip

Source Field Order - Selects the field order for the source video (must be the same field order that the source clip was made with)

Destination Field Order - Selects the field order for the destination timeline (must be the same field order as the timeline)

Convert - Selects the direction of conversion, PAL -> NTSC or NTSC -> PAL

Progressive Output - this option forces the output to be de-interlaced De-Interlace Options - this governs the type of de-interlacing algorithm used in the standards conversion and progressive output. Normal is the default. Smart takes a little longer to render but may produce better results. View smart mask allows you to see the smart de-interlace mask as a diagnostic tool to allow you to set the tolerance correctly.

Tolerance - Defines the tolerance of the Smart de-interlace mask.

Film Conversion uses the G Film Converter plugin to convert Film from and to video frame rates. This is a more complex filter than G Converter, but it uses a similar method of operation and algorithms.

NTSC to FILM Conversion

Note: G Film Converter is designed for producing a video to film standards conversion. For removing the 3:2 pulldown on film telecined to NTSC video, use Apple's Cinema Tools instead.

To convert from NTSC video's 29.97 frame rate to film's 24 frames per second, G Film Converter uses an algorithm similar to reverse 3:2 pulldown as used in the Film Effects set of plugins. Form more information on this it is advised to download and read the instructions for Film Effects. G Film Converter allows you to pick from one of the same five methods that Film Effects uses as outlined below:

1 Field - Picks the nearest field to the "right" one 2 Field - Picks the nearest field, and blends it with it's neighbour 2 Field Adv - Picks the nearest field, and blends a percentage of it with a percentage of it's neighbour 3 Field - Picks the nearest field, and the one before and the one after and blends all three 3 Field Var - Picks the nearest filed, and the one after or the one after and one before, in a 3:2 pattern

The more fields used, the smoother the result, but be prepared for an increase in motion blur.

1 Field - Can look very good when de-interlace is set to Normal - looks choppy on Smart de-interlace 2 Field - Looks very good with both Normal and Smart De-interlace 2 Field Adv - Looks very good with both Normal and Smart De-interlace - produces the best result in many tests 3 Field - Has a very smooth look, but also has the most added motion blur 3 Field Var - Also has a very smooth look, but also can look like an NTSC kinescope (tele-recording)

FILM to NTSC Conversion

Film to NTSC conversion simply adds 3:2 pulldown to the NTSC video to produce the 29.97 frame rate.

PAL to FILM Conversion

PAL to FILM conversion uses one of two methods. The first method slows down the PAL frame rate of 25fps to 24fps then matching each frame of video to a frame of film. This produces an excellent looking conversion. This method is the traditional method used to transfer PAL video to FILM as a telerecording. It was actually done by running the film recorder at 25fps so that it matched with the scan of the special TV screen used.

The second method removes one frame every second to reduce the PAL frame rate from 25fps to 24fps. This would produce a stutter or jump every second, so instead of removing the frame all at once, it is removed a field at a time, so in fact, one field is removed every half-second. I have called this PAL-1 to Film Conversion. This method has the advantage that the speed of the resulting film is identical to that of the video.

FILM to PAL Conversion

FILM to PAL Conversion uses the same two methods that PAL to FILM Conversion uses, but in reverse. For converting FILM to PAL, the film rate of 24fps is sped up to 25fps, then matching each frame of film to a frame of video. Again, this produces excellent looking results.

The second method, in this case called Film to PAL+1 Conversion, adds one field every half-second to change the Film's 24fps to PAL video's 25fps. Source Clip - An "image well" where the source PAL or NTSC clip must be dropped

Source Pixel Size - Selects the pixel dimensions for the source PAL or NTSC clip

Source Field Order - Selects the field order for the source video (must be the same field order that the source clip was made with)

Destination Field Order - Selects the field order for the destination timeline (must be the same field order as the timeline)

Convert - Selects the direction of conversion, PAL -> 24p, FILM -> 24p, PAL-1 -> 24p, 24p -> PAL+1, NTSC -> 24p, 24p -> NTSC

Progressive PAL - When converting PAL to 24p this option forces the PAL video to be de-interlaced

Progressive Output - this option forces the output to be de-interlaced

De-Interlace Options - this governs the type of de-interlacing algorithm used in the standards conversion, Progressive PAL and progressive output. Normal is the default. Smart takes a little longer to render but may produce better results. View smart mask allows you to see the smart de- interlace mask as a diagnostic tool to allow you to set the tolerance correctly.

Tolerance - Defines the tolerance of the Smart de-interlace mask.

Notes on Audio Sync

Standards Conversions normally preserves audio sync. This has been successfully tested on PAL -> NTSC and NTSC -> PAL, 24p -> NTSC, NTSC -> 24p, PAL-1 -> 24p and 24p -> PAL+1. Converting to and from 24p and PAL via the speed up (approx 104%) / slow down (approx 96%) method will cause the audio to no longer sync to the picture. In this case the audio should be selected and either sped up or slowed down to match the video. External audio editing packages can also perform this task to perhaps a higher quality than FCP can.

Final Cut Pro alters the audio speed slightly itself to help in the standards conversion process. In converting PAL to NTSC, it would seem that if PAL's 25fps was converted to NTSC's 30fps, this would cause issues because NTSC is not exactly 30fps but 29.97fps. However, if the code is set to treat NTSC as exactly 29.97 then audio sync is lost, and in treating NTSC as exactly 30fps it is preserved. The only explanation for this contradiction is that FCP is slightly altering the speed of the audio behind the scenes. It is also not known wether when converting NTSC to FILM speed wether it is best to convert to 23.98 or 24 fps, although it is suspected that by the above logic, FCP itself may handle the slight audio speed conversion necessary.

Notes on PAL <-> 24p Conversion

When converting we use a nest of the original clip as a place-holder for the conversion effect. The movie information comes from the movie dropped on the source image well. This works excellently in most cases, but with PAL to 24p conversions the length of the final clip changes. When converting to 24p, the resulting clip is too long, and when converting to PAL it is too short. In the case where it is too short, it is easy to remove the duplicated frames by shortening the clip. To make it longer is more tricky. The method I have found works is to add black slug to the end of the clip to make it the 4% longer that it needs to be, and select both clips before nesting, so that the nest becomes longer. Notes on the Standards Conversion Filter Operation

Once the original clip has been added to the source image well, the nest can be edited (in or out points moved) or moved in time. The original clip that is added to the timeline must be the clip that is used to drop into the source image well. Any difference in the in/out points will not give the desired result.