Convert short films from 23.976 to 29.97 for TV broadcast

Posted by Lisha 
Convert short films from 23.976 to 29.97 for TV broadcast
December 01, 2013 08:27AM
Hello all,

Looking for the best workflow and help with sync issues.

Editing in FCP 7.0.3. I edit a short film showcase for national syndicated television broadcast. In the past we've delivered in SD but will now start delivering, HD/1920 x 1080. 3 of the films for our next episode are 23.976 fps. and each are 8-12 minutes long. For the conversion from 23.976 to 29.97 I used Compressor (3.5.3) to change the frame rate but the audio drifts out of sync. The audio was set to pass-through. I used Larry Jordan's tutorial for reference ( Per a thread I found within Creative Cow, I tried it again this time rendering the audio (AAC, Stereo, 48kHz, Better, Average Bit Rate, Target Bit Rate 128) however the audio is still drifting out of sync. Not as much as when I did the conversion with audio-pass through, but by the end of each film audio is still 1-2 frames out of sync when rendering the audio. How do I convert the films to 29.97 for television broadcast? I also have After Effects but am not very savvy with the program and Adobe Media Encoder.

Once I convert the films to 29.97 I can edit/assemble the show as usual, taking into consideration the new sequence settings for HD delivery, correct? If not, please advise as to what my workflow should be.

Thanks so much,
iMac, 3.4 GHz Intel Core i7
Promise Pegasus
Black Magic Design Ultrastudio mini monitor to Boland Broadcast monitor
Re: Convert short films from 23.976 to 29.97 for TV broadcast
December 01, 2013 08:32AM
Does the delivery need a file or HD tape? For HD tape delivery, generally the HD-SDI card / box will accept 23.98fps material and add in 3:2 pulldown on output to the recording device, meaning you don't have to physically add the pulldown yourself.

It is possible to add 3:2 pulldown as a render process. This is best done to completed content (rather than pieces) so that the entire output is in constant cadence (the 3:2 pattern has no breaks or gaps in it). I can help you add 3:2 as a render process with my plugins if you're interested, but I'd first want to know this is right for your delivery.

Re: Convert short films from 23.976 to 29.97 for TV broadcast
December 01, 2013 11:04AM
Hi Graeme,

Thanks for the response! I am delivering the entire 58:30 show as a file. The post house adds the closed captioning and satellites the show. 3 films are 23.98, 2 films are 29.97. I incorporate the short films, graphics, opening titles, end credits, commercial blacks, etc.,... to make up the 58:30 show.

Re: Convert short films from 23.976 to 29.97 for TV broadcast
December 07, 2013 04:55PM
Lisha: Are you sure the audio "drifted out of synch" by 1-2 frames in 8.5 minutes? That is hard to detect. Whenever you transform 23.976 fps to 29.97 fps there are tiny frame errors. For example , 1002 frames of original is expected to make 1002 x 1.25 = 1252.5 frames. That is impossible. It can make 1252 or 1253 frames instead. Depending how the transform is done, this can appear as a 1 frame synch error. The tiny errors keep occuring but are not cumulative.

It is very important to know, and to say, whether the 29.97 fps video you're making is progressive (29.97p) or interlaced (59.94i). Many broadcasters will accept either one. You can avoid interlacing artifacts with 29.97p, but 59.94i offers an easy solution for the rate change. Graeme suggests how to use 3:2 pulldown when transforming from 23.976p to 59.94i. 3:2 pulldown is a standard, generally acceptable way for that.

Larry Jordan's tutorial shows a weird example in which the original 23.976 fps video is interlaced. Who has ever encountered 47.952i? He uses Compressor to transform it to interlaced 29.97 fps (59.94i). To transform from one interlaced field rate to another is very difficult, and Compressor is bound to make a mess. Larry Jordan chooses "Better" for the rate conversion and gets a mess. He finds three fields of the original visible to varying degrees in most "frames" of the transform. If Larry Jordan's original had been 23.976p, and had he chosen "Fast" for the rate conversion, Compressor would have done the sensible 3:2 pulldown to make the 59.94i.

Compressor does 3:2 pulldown of 23.976p to 59.94i when the Rate Conversion is "Fast". In Video Settings you must specify the 29.97 frame rate and "Interlaced" as well as the desired field dominance (e.g., "top first" ). In Frame Controls you must specify "Top first" (assuming that's your choice) in "Output Fields". "Rate Conversion: Fast..." is the default in Frame Controls.

For transforming progressive-to-progressive, like 23.976p to 29.97p, in Compressor, the "Fast", "Good", "Better", and "Best" settings give very different results. "Best" uses serious optical flow. Its results vary from awesome to awful.

"Better" or "Best" can sometimes do 23.976p to 59.94i better than 3:2 pulldown. I assume Compessor uses optical flow to transform the 23.76p to 59.94p from which it then slices 59.94i. (Optical flow could also handle interlaced-to-progressive and interlaced-to-interlaced, but these require double deinterlacing the original, which Compressor probably wouldn't do.)

Dennis Couzin
Berlin, Germany
Re: Convert short films from 23.976 to 29.97 for TV broadcast
December 10, 2013 02:38PM
Thanks so much Dennis!!!! Lisha
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