Video encoding and progressive output on HDTV
I've finally upgraded my HDTV from the original Mitsubishi WS-55411 to a new HP MD5880N 58" 1080p DLP display. In doing so, I am going to be really excited to get my HTPC all hooked back up again and test out larger desktop sizes, as well as see how the XBox content from XMBC looks on it.

It has also prompted me to get back into learning more about video encoding and interlacing/deinterlacing formats. Especially concerning some of my DirecTV standard def content with massive field order flipping and non-standard GOP length encodes. Most irritating is animated source material, like South Park with obvious interlaced combing effects on computer and HD progressive displays. I'm finding that standard def content and the way they variable encode GOP and do stream/field order flipping can be devastating for some progressive display's ability to gracefully handle the deinterlacing correctly. For good reads on general video editing, check out Nicky Guides and Home Theater HiFi Progressive DVD guide.

I found a cabinet that seems like it will fit, and it has closed glass doors so that my 1 and 3 year old won't be fiddling with the components.


The HP MD5880N claims to support the following formats:

• 2 HDMI (480i/p, 720p, 1080i/p*)
  
• 2 Component (480i/p, 720p, 1080i/p**)
  
• 1 VGA (480i/p, 720p, 1080i/p***)
  
• 1 USB
  
• 1 Serial
  
• 3 Composite/Svideo
  
• 2 Cable
  
• 1 CableCard
  
• 5 Analog RCA Audio
  

* Supports 24, 30 and 60fps.
** Supports 24, and 30fps.
*** Supports 24, and 30fps but we have heard that the maximum resolution is 1280x1024p60

You've probably heard/read before, how 3:2 pull down interlacing or "telecine" conversion works. You end up with combing effects where the exclamation points are in the diagram below when converting 24fps to 30fps interlaced NTSC content (what is called 480i and has been the standard def broadcast for well over 30 years). The artifact comes from essentially having two halves of different frames combined to get an interpolative frame in between when stitched back together to make a progressive frame for display on a high definition display. In most cases, this doesn't cause too much problem, but when there is a lot of "differences" between two adjacent original frames (like during fast motion content or scene changes), you could end up with some VERY nasty displays on progressive output:




Another example of a problem with displaying telecined content on a progressive display is detailed below, where a scene from "Battlestar Galactica 2003" shows a scene transition on one of the interlaced transition frames when doing 3:2 pull-down conversion from 24fps to 30fps. The first image is the final interlaced frame. Following that are the individual half-frame A and B fields that came from two separate 24fps content frames when being telecined (essentially a merger between two very different fields across a "scene transition" from the diagram above where the exclamation points are).



What isn't obvious from all this, is if this new HP TV supports actual native 24fps display play back, or merely supports converting from 24fps FILM MPEG-2 input content to 30 or 60fps NTSC progressive content as detailed in the flow below of a scene from "The Fifth Element" (image taken from Home Theater HiFi):


A problem develops with this process when the progressive display process performs an inverse telecine back to the original 24fps and essentially drops every third field of five, then returns to the original 24fps full frame content. Then a DIFFERENT progressive 3/2/3/2 full frame duplication is made to end up with 4 frames -> 10 frames conversion (turns 24fps into 60fps). The problem with this, is it ends up making motion sensitive footage a bit "jerky", because you spend 3/10ths of the time on one frame and 2/10ths of the time on the next.

So, why can't today's HDTV's simply display the raw native 24fps original FILM content at 48fps or even 72fps and keep a more symmetrical "weighting" of each frame? What isn't clear to me, is does my new TV actually essentially DO this (and do it even on component inputs from the specs above), or does it simply accept this as an input and effectively do the conversion from 24fps to 60fps with jitter (along with upsampling to 1080p) internally, as per the diagram above?

I need to find a good DVD test pattern/encode that I can run through my DVD player (and xbox media player) and test how my DVD and TV deinterlacers work. I've also heard that some of these newer TV's with 1080p support may "cheat" and drop the B-field and simply then line double the A-field (or vice-versa), rather than deinterlace the 1080i input content to a fully progressive 1080p signal for display. If it were to do this, a simple single line resolution test pattern at 1080 horizontal lines should quickly expose this. I need to find content like this for more than just test patterns, but also various nasty DVD encode/frame rate (it should be possible to expose 24fps converted to 30fps progressive as well, since you would have jerky motion). I'm not sure if Digital Video Essentials DVD will do what I want or not...Probably not.
- posted by Jeff @ 10:54 PM