Family Channel uses 4:1 pulldown? Ughh, how do I fix this in handbrake - Canadian TV, Computing and Home Theatre Forums
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post #1 of 5 (permalink) Old 2011-12-22, 02:12 PM Thread Starter
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Family Channel uses 4:1 pulldown? Ughh, how do I fix this in handbrake

I noticed something strange about Family channel HD that I've never seen any other channel ever do. During shows like, "Shake it Up", they seem to be using some sort of 4:1 pulldown telecine.

The show is originally a Disney Channel show, and like all Disney Channel shows these days it's shot in 720p24. The Disney Channel in the US broadcasts in this native format. In Canada, Family Channel broadcasts in 1080i and instead of doing proper 2:3 pulldown telecine they seem to be doing some odd form of 4:1 pulldown that I've never seen before. That is, repeating every 4th frame of the original 23.976 show to bump it up to 29.97 but with no interlacing artifacts.

This is the completely WRONG way of doing a standards conversion from 720p24 to 1080i30 as it causes some very strange judder. In any case, how do I get Handbrake to deal with this? The pullup filter assumes 2:3 pulldown and it doesn't seem to work properly on episodes of "Shake it Up" recorded from Family Channel. I tried just forcing the framerate down to 23.976 during my transcode without using the pullup filter, but that seems to drop the completely wrong frames causing even worse judder. What I need is some type of 4:1 decimation filter I think.
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post #2 of 5 (permalink) Old 2011-12-25, 08:50 AM
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Do the broadcasters actually use those fractional frame rates, such as 29.97? Those odd numbers came about back when NTSC colour was introduced due to the method used to include colour (prior to that, B&W TV used an even 30 frames/second). There's no reason to use them with digital TV. Also, telecine pull down is method of matching up film frames with video. It wouldn't be used with video conversion.
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post #3 of 5 (permalink) Old 2011-12-26, 04:42 AM Thread Starter
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Yes, broadcasters continue to use fractional framerates even in ATSC to make downconversions to NTSC easier.

As for IVTC, yes it would be used for conversion. Anytime you record something that was shot on film originally it's usually telecined as you mentioned. But when transcoding, it's more efficient to remove this telecine process (ie. Inverse Telecine) by restoring the original frame rate of the filmed footage and storing it an actual 24p (progressive) video file rather than keep it as a 29.97i (interlaced) file. A filter such as "pullup" does this procedure during encoding in Handbrake by matching up fields that are from the same film frame and discarding the extra duplicate field that exists for every 5 fields of video; thereby restoring the originally shot film footage to 24 fps (technically 23.976 fps) from the 29.97fps ATSC/NTSC video recording off ATSC/NTSC television. I do this all the time when recording movies from Superchannel, HBO Canada, or Movie Central.

The only problem is, Family Channel seems to be doing it wrong; it is using an odd 4:1 cadence pattern that Pullup can't seem to deal with instead of the usual 2:3 pattern.
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post #4 of 5 (permalink) Old 2011-12-29, 05:07 PM
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Sounds like you don't need to telecide (since it's not telecined), but to simply decimate every 5th frame. Don't ask me how in Handbrake though as I don't know off-hand.

[Edit] Thinking about it, are you sure it's not soft-telecined and you simply need to ignore the repeat flag instead of doing IVTC?
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post #5 of 5 (permalink) Old 2012-01-07, 02:24 PM Thread Starter
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No it's definatly not soft-telecined. Soft-telecined (in comparison to hard-telecine) would show up in mediainfo as an actual 23.976 transport stream in the metadata (as opposed to 29.97). Like a soft-telecined stream, Family HD doesn't exhibit any interlacing artifacts but it shows up as a 29.97fps file; seemingly in a quasi progressive format (30p).

If a transport stream is recorded at 29.97 it usually is in one of two format: hard-telecine, or video interlaced. Soft-telecined is the same thing as native progressive and would show up as an actual 23.976 transport stream (often used on DVD and Blu-Ray but never for HD broadcast). Both 29.97 formats would exhibit some sort of interlacing artifact when stepping through frame by frame. In the case of a hard telecine, you'd see 3 frames without artifacts, then 2 with artifacts, repeated over again. In the case of video interlaced material, every frame would contain interlace artifacts.

However this is definately neither. it's a 29.97fps transport stream that exhibits no interlace artifacts yet contains a duplicate frame every 5th frame. Again, I strongly suspect that this is merely Family-HD using an incorrect telecine process from the 720p master tapes they receive from Disney Channel. In the US, Disney Channel shoots all of their shows progressively (24p) and broadcasts at 720p60 (using a 2:3 frame repeat process similar to 2:3 field based telecine).

It just iriates me that Video Engineers at these stations have no clue what they are doing. If Family Channel wants to broadcast in 1080i30 that's fine, but they have to adjust their standards converters such that any ingress footage from 720p hard telecine sources are properly broadcast using field-based 1080i telecine.
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