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4:1 telecine on Family Channel in Canada, what do I do?

Posted: Thu Dec 22, 2011 6:14 pm
by mcpish
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.

Re: 4:1 telecine on Family Channel in Canada, what do I do?

Posted: Fri Dec 23, 2011 5:54 am
by musicvid
I don't know the best way to handle this in Handbrake, but full-frame ABCDD is the oldest form of NTSC telecine in existence, which either makes me quite old or you quite young, or both. It's not really "pulldown" because it is frame-based, not field-based.

It's possible you could drop it into a nonlinear editor, change it back to 23.976 (dropping every fifth frame without resampling), then render anew with a proper 2:3 pulldown. But with set-top recorders (and all PVRs for that matter) it's a good idea to run the files through VideoRedo first to fix indexing errors from the broadcast stream.

Re: 4:1 telecine on Family Channel in Canada, what do I do?

Posted: Fri Dec 23, 2011 8:41 pm
by mcpish
Thanks for the reply.

You're right, "ABCDD" is the right way of explaining it. I've just never seen it before, usually telecine is field-based as far as I've seen, but I'll take your word for it.
Yeah I use VideoREDO to edit out the leading/ending footage before the start-times and end-times of my programs. When it renders the file out it should fix anything that is "wrong", but it didn't really find anything like that. I just wish Handbrake had a few more filters to choose from instead of just Pullup, Decomb, and Deinterlace. It really needs some kind of decimate filter than you can manually enter values for "ie. ABCDD" or "4:1" or something like that.

I often run into other scenarios where if I record a show that was obviously shot on film (23.976fps) from a channel that broadcasts in 720p60 (like ABC, and CBC), where I have drop the duplicate frames reducing the framerate from 59.94 > 23.976; Surprisingly I've found that Handbrake's PullUp filter does this just fine, as long as I enable the pullup filter and FORCE the framerate to a constant 23.976 (same-as-source keeps it at 59.94). Although, technically I know it's overkill. Since in these cases (720p60 channels) there's no need to match-up interlaced fields as there would be in a 1080i30 stream; a simple 2:3 decimation filter would have done the same thing for film content on 720p60 channels.

I do a lot of video-transcoding with handbrake from recordings I make from my MythTV PVR. I've been doing this for a few years now (I'm 33) and have learned a lot but by no means an expert. The thing that I find really mind-boggling when I think about it is the number of "exceptions" and "special cases" I've come to understand over the years. I use HandbrakeCLI most of the time and I've created a custom script that will deal with the different "types" of video I run into. After I edit my videos in VideoREDO my script is designed so that I have to name the video file with a specific extension such as (1080i.mpg) or (720p60tc.mpg) depending on what I want handbrake to do. Then after I finish editing all my videos, they are sitting in a certain directory. I then run my script and the script matches up the extension to a section of the script that does exactly what it needs to do in handbrake depending on what type of video it is (IVTC, decomb, force framerate, leave variable fps, etc).

Another trick I've learned is that when recording shows that were shot on film (23.976) off Network TV:
When enabling the pullup filter in Handbrake make sure you tell it to ignore the bottom 240 lines from a 1080i channel (ie. --detelecine=0:0:0:240:0:0:-1)

Why? Because usually TV stations put those annoying animated screen-bugs on top of the show. BUT, those bugs don't match the 2:3 cadence pattern of the underlying film material. They often contain inter-field motion (60Hz). If you don't tell Handbrake's pullup filter to ignore the buttom 240 lines, whenever a TV station decides to animate its logo the entire video will become jumpy as the Pullup filter gets confused as to what frames to drop (since it can't match them up perfectly anymore due to the inter-field motion of the bug) and will often drop the wrong frames. By ignoring the bottom 240 lines, you're assured that the underlying show is IVTC'd properly since pullup will ignore the area of the screen where any bugs would appear and since there are still well over 700 scan-lines that is more than enough for pullup to make a correct decision in my experience. You'll end up with a slightly choppy bug animation (which isn't noticable) instead of a choppy video whenever a bug moves around (which is very noticeable). That's just one of the tips I've learned that most people don't do when IVTC'ing TV shows.

A friend of mine asked me to help him setup a similar setup but I've realized there's no good automated way to help him with his transcoding, it requires a LOT of deep knowledge about how Interlacing works, what is telecine? The difference between how 1080i channels vs 720p channels telecine content, etc. You have to be able to recognize what type of video is what using something like mplayer and stepping through frame-by-frame for a few seconds, for instance to recognize the "interlaced, interlaced, non-interlaced, non-interlaced, non-interlaced) pattern of telecined material in files, or to notice when stepping through a 720p60 file wheather it was shot on film (2 duplicate frames, then 3 dupes) or shot with a video camera (60 unique frames every second).

It's no wonder now I see so many errors done with transcoding even by TV stations. It's quite difficult to understand for most people I think.