How to tell when to detelecine
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simplesimon
- Posts: 25
- Joined: Wed Sep 07, 2011 10:54 pm
How to tell when to detelecine
Most of the time when I transcode something that has been hard-telecined, or a bad combination of pal conversion + hard-telecining, I end up with a vfr between 24.xxx and 25.xxx. But I've got a few that end up with a vfr of 26.xxx or even 28.xxx. Maybe not for the 26 vfr example but I'm thinking for something that comes out with a vfr above 28.xxx I should just not detelecine because it probably really is supposed to be at 29.97. Anybody know what the most accurate thing to do is in this case?
Re: How to tell when to detelecine
The video is probably a combination of both Telecined film footage (23.976) and NTSC/ATSC video footage (29.97). Lots of documentaries in NTSC-Land are like this. The only way to handle them in Handbrake is it to use Variable-framerate with BOTH the ivtc filter and decombing filters on. This isn't perfect, since Handbrake will occasionally screwup and sometimes miss something but it's the best you can do, until the day when Handbrake includes PROPER field-extention deinterlacing (60Hz motion).
The way to tell if something needs to be detelecined (as opposed to deinterlaced/decombed) is to open the video file in a player that you can easily step through the video on a frame-by-frame basis (mplayer is good for this, you can use the . (period) key to step one frame ahead at a time). Quickly scan to a scene with movement and step through it frame-by-frame. If it's something that needs to be interse telecined you'll notice a pattern every 5 frames. You'll see 3 perfect frames with no interlacing artifacts, followed by 2 frames that have visible combing. This pattern will then repeat over and over again (3 perfect frames, 2 frames with artifacts). In this case, TURN ON the IVTC filter and TURN OFF decombing and FORCE the framerate to 23.976 fps.
If however you see more than 2 frames in a row with combing artifacts than the video is either entirely interlaced (shot on video and needs to be decombed/deinterlaced) or it could be a mix of progressive and interlaced scenes. You might want to quickly scan to an entirely different part of the video and do this step-through process again at a few key points in your video to see if this behavior changes. If it's always the same, ie, you always see the 5-frame repeating pattern, then it's definately telecineed and you can feel safe using IVTC and forcing the framerate to 23.976. If you always don't see the pattern (more than 2 frames in a row with visible combing) then it is definately interlaced and you should turn the framerate to 29.97 and TURN ON the decombing filter and TURN OFF IVTC. If it varies and you notice there are some scenes with the 5-frame repeating pattern and some without, then turn on VFR (Variable Frame Rate) and TURN ON both decombing and IVTC.
I've learned this from quite a bit of trail and error over the years doing transcodings from my HD MythTV PVR.
The way to tell if something needs to be detelecined (as opposed to deinterlaced/decombed) is to open the video file in a player that you can easily step through the video on a frame-by-frame basis (mplayer is good for this, you can use the . (period) key to step one frame ahead at a time). Quickly scan to a scene with movement and step through it frame-by-frame. If it's something that needs to be interse telecined you'll notice a pattern every 5 frames. You'll see 3 perfect frames with no interlacing artifacts, followed by 2 frames that have visible combing. This pattern will then repeat over and over again (3 perfect frames, 2 frames with artifacts). In this case, TURN ON the IVTC filter and TURN OFF decombing and FORCE the framerate to 23.976 fps.
If however you see more than 2 frames in a row with combing artifacts than the video is either entirely interlaced (shot on video and needs to be decombed/deinterlaced) or it could be a mix of progressive and interlaced scenes. You might want to quickly scan to an entirely different part of the video and do this step-through process again at a few key points in your video to see if this behavior changes. If it's always the same, ie, you always see the 5-frame repeating pattern, then it's definately telecineed and you can feel safe using IVTC and forcing the framerate to 23.976. If you always don't see the pattern (more than 2 frames in a row with visible combing) then it is definately interlaced and you should turn the framerate to 29.97 and TURN ON the decombing filter and TURN OFF IVTC. If it varies and you notice there are some scenes with the 5-frame repeating pattern and some without, then turn on VFR (Variable Frame Rate) and TURN ON both decombing and IVTC.
I've learned this from quite a bit of trail and error over the years doing transcodings from my HD MythTV PVR.