2:2 pulldown & 3:2 pulldown detection in software players

M

Mandarin Man

Guest
Hi,

WinDVD and PowerDVD's manuals don't mention anything about 2:2 pulldown and 3:2 pulldown detection, but I assume their MPEG2-decoders have this function, right? I use PowerDVD and it only allows me to set it's video mode to Auto-select, Force bob or Force Weave. I guess when leaving it at auto-select the decoder would automatically detect film source material, ignore 3:2 pulldown flags if necessary and perform a simple weave without quality loss, wouldn't it? You see, I have the video mode set to auto-select, yet when I play a movie on DVD, the PowerDVD configuration window tells me it's using bob, which seems like it doesn't recognize the material to be frame-based. Should be weave..

Can anyone clear this up?

Now onto HDTV 1080i50/60 TS-files from film sources.. Are HDTV 1080i60 TS-files 48i + 3:2 pulldown flags (like NTSC DVDs) or 60i (with duplicated fields actually in the video)? Will software players handle this the same way as DVDs from film sources (ignoring the 3:2 pulldown flags)? I use VLC to play TS-files. Does VLC have 2:2/3:2 pulldown detection? When deinterlacing is set to disable, it shows interlacing artifacts when there's motion. What deinterlacing method should I use if I want VLC to perform a simple weave on film source material?? (just combining the 2 fields into the original film frame without any quality loss) It offers blend, bob, discard, lineair and mean.. (which are all for video source material, if I'm not mistaking). I would think blend. Is blend the same as weave?

Very curious about this..

Roy
 

drummerjohn

Well-known Member
2:2 pull down is used on PAL material and 3:2 is used on NTSC. Almost all DVDs are correctly flagged so that the player will know what to do with it.

As for VLC - not a clue.
 

Mr.D

Distinguished Member
blend is probably some sort of averaged frame. Takes first field makes it full height does the same with the other field and then does a 50/50 mix between the two.

bob will be a classic scaler bob ( takes each field makes it full height and doubles the frame rate. ( normally the one to use if all else fails and on field based material ).

discard is probably dropping every other field and bobbing the rest ( some machines can't cope with the data-rate requirement for a bob deinterlace)

mean ....some sort of slightly more elaborate blend maybe does a minimum process rather than a mix.

linear...some sort of bob with a really nasty cheap scaling algorithm probably.

With VLC if it doesn't do 3:2 pulldown detection which your material (1080i 60Hz) most likely contains (its unlikley to be flagged if its a recording from US tv)) the only one which will show no interlace artifacts and give "acceptable results" is the bob. I've always found the bob in VLC to be a little unstable though. Your refresh rate will also play a role. If you can't get VLC to do 3:2 pulldown detection and drop the correct frames ( inverse telecine) it will display as a 60fps sequence of frames , if your refresh rate is not a multiple of 60 it will either drop frames or repeat them to reach the refresh rate either way will create judder ( regular frame repeats are not too distracting in my experience , frame drops are terrible though).

NTSC dvds from film originated material are not "48I with 3:2 pulldown flags" Its 60i with the pulldown fields flagged so they don't have to be stored with the same precision twice...the distinction is important as the disc will only ever decode as 60i before handling by a deinterlacer even if it reads the flags assuming they are correct.( remember mpeg2 is a bunch of data that reconstructs a video sequence when its decoded properly, its not fields or any sort of coherent video structure on the disc its just data until its been decoded)

If you had pal material originated from a frame based source you could leave it on no deinterlace and it would ( should) do a simple weave and essentially deinterlace correctly.
 
M

Mandarin Man

Guest
Thanks, Keith.

As for the first part of my question, WinDVD and PowerDVD's decoders have 2:2 pulldown and 3:2 pulldown detection, right? Interesting they don't mention this in their specs. I guess it's just weird then that PowerDVD doesn't switch to weave when inserting a DVD movie, probably a bug. I have an older version..

BTW, If I'm not mistaking, most software MPEG2 decoders use flag-based 3:2 pulldown detection, so they might not handle unflagged (cadens-based ) 3:2 pulldown material that well..

Mr.D said:
If you had pal material originated from a frame based source you could leave it on no deinterlace and it would ( should) do a simple weave and essentially deinterlace correctly.
Would this be the player or your videocard?

Roy
 

Mr.D

Distinguished Member
Cadence detection can take place either in the software or the hardware.
Most do use the flagging , some actually try and detect and some will do both and some will allow you to manually select . I'm not familiar with windvd and powerdvd these days.

The reason for not solely relying on the flagging is down to less that accurate mastering although I have to say I've never seen a commercial release that had bad edits that would destroy the cadence.

The hidef stuff will not have flaggging, if the software can't detect the 3:2 pulldown sequence or if its been mucked up in the recording dropping to a bob will at least hide the interlaced artifacts at the expense of resolution. This is essentially the fallback mode for many deinterlacers.
 
M

Mandarin Man

Guest
Mr.D said:
If you had pal material originated from a frame based source you could leave it on no deinterlace and it would ( should) do a simple weave and essentially deinterlace correctly.
Would this be the player or your videocard?


What software players / decoders feature cadence pulldown detection?

Incidentally, what software DVD player/decoder do you use, Keith?
 

Mr.D

Distinguished Member
Mandarin Man said:
Would this be the player or your videocard?


What software players / decoders feature cadence pulldown detection?

Incidentally, what software DVD player/decoder do you use, Keith?
I use Theatertek 2 in software mode with ffdshow. (makes no use of any hardware abilities on your graphics card it all happens in software when used in this way). It has numerous mind boggling deinterlacing options that vary depending on what graphics card you have and what mode you choose . I use auto which essentially just reads the flags... I have my doubts about it working correctly with some PAL discs but its something I haven't had the time to investigate.

If you use "smart" with theatertek it will do cadence detection but you need to either run with the nvidia post processor which has some image quality issues of its own or use a suitable nvida card which will do detection in hardware.

Getting back to to your first question.

The setting for doing a simple weave will likely be in the software (essentially a weave is no deinterlacing as its merely a question of combining the fields in the right order.) In some software its even referred to as "off" ( the digiTV playback app for the nebula card for example).

I can't tell you off hand what software does and doesn't do on the fly cadence detection rather than read the flags beyond what I've told you about theatertek.

It can be done in software and it can be done in hardware.
Neither method should be better than the other if they are done correctly.

Deinterlacing field based material is a different ball game though there is a limit to what type of deinterlacing you can manage in realtime on domestic kit. 99% of the time it will be a bob of some description. ( This is really proper "deinterlacing...with frame based material its actually a simpler process and is often referred to as "inverse telecine")

Dscaler4 is a good app to have a play with if you want to see different deinterlacing methods in action and have a video capture card handy. I still use this pipeline for problematic material and most video based titles as I think it does a better job than all the other available sofware solutions.
 

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