Monday, April 23, 2007

Why Frame Rate Matters

I saw the following in MythTV's forum (MythTvTalk):
"Once the video is captured in the file (...), you are past any PAL/NTSC differences..."

While this is true in some aspects, it's very wrong with regards to one important aspect: frame rate. Why is frame rate important? Because there's no way to do interpolations on time.

Let's think about it this way - if your monitor is set to 1024 x 768 and the movie you're watching is using a different resolution, it's relatively easy to scale the movie to fit the entire screen - scaling using various methods of interpolation has been done a lot. In most cases, it's the video card that does the scaling, so it doesn't even affect your computer playback performance (scaling doesn't work well on interlaced video, which is one of the reasons I think interlaced video sucks, but that's the topic for another post).

If your monitor is set to 60Hz (it's practically showing 60 fps), and you're watching a PAL movie that runs at 25 frames per second, there's no way to interpolate 60 frames out of the existing 25 frames. Instead, during playback frames are repeated so that the overall speed of the movie is maintained.

Here's an easy example, and let's assume that NTSC runs at exactly 30 fps for simplicity: If your monitor is set to 60Hz, and you play a 30 fps NTSC movie, each frame is shown for two progressive scans of the screen - the frame rate is maintained exactly, and the quality and smoothness of the video is excellent.

But now try to watch a 25 fps PAL movie using the same monitor. Now you have to fit 25 original frames into 60 display frames. That's 5 original frames into 12 display frames (in 1/5 of a second). There's no way to spread the frames evenly. Let's assume an original frame switch is done as soon as it should be shown, but not within a display frame (otherwise you'll see a discontinuity at a certain vertical position, whenever there's horizontal motion between frames). That's the way DirectShow works on Windows. In this case, here's how 1/5 of a second would look like:



After this conversion, some of the frames would be shown for 1/30 of a seconds, and some would be shown for 1/20 of a second, there's actual a rhythm here: 3,2,3,2,2. This rhythm will repeat itself 5 times per second throughout the video you're seeing. The visual result of this is called judder, and is especially common when converting films to NTSC.

How annoying is this jitter? Many people wouldn't be able to spot the problem, but the video would looks a bit jumpy. It's especially visible in scenes of consistent (and slow) horizontal movement of the camera (panning).

Connecting your PC to a TV

What if you have a TV-Out option on your display card, and you hook your PC to a TV? Will this solve the problem? The TV shows 25 fps, and the movie also has 25 fps, but there's no way to skip the 60 fps of the display adapter (actually, some display adapters lock the frame rate to something sensible when the TV-Out is turned on, but let's assume you can feed a PAL TV from a display card showing 60 fps).

In this case the result is even worse. The display adapter has to convert the 60 fps back to 25 fps without knowing the original material was in 25 fps. This would probably look like this:



What happened here? The first original frame (red) is shown without a problem, but by the time we need to show the second frame (on the TV), the second video frame (yellow) is not yet shown, so the red frame will be shown once more. The outcome is that out of every 5 frames, one will be repeated, and one will be skipped. This is a pretty noticeable judder.


What's the Solution?

In some cases it's quite simple - if you're using your PC to watch video, make sure the display refresh rate matches your video's frame rate. If you watch PAL movies, set your display to 75Hz or 100Hz. If you watch NTSC movies, it sounds like you should set your display to 60Hz (or 90Hz or 120Hz), but most NTSC shows are actually filmed at 24 fps (film rate), so the best frame rate is a multiplication of that, probably 72Hz.

Is that all?

No, of course not. Many people in Europe want to use their computers to watch both shows they recorded using a capture card (which will be recorded at 25 fps) and movies or US TV shows (which are recorded at 24 fps). How do you set your monitor's refresh rate in this case? I'll leave that to the next post.

16 comments:

Jerry said...

cheap wedding gowns,
discount bridal gowns,
China wedding dresses,
discount designer wedding dresses,
China wedding online store,
plus size wedding dresses,
cheap informal wedding dresses,
junior bridesmaid dresses,
cheap bridesmaid dresses,
maternity bridesmaid dresses,
discount flower girl gowns,
cheap prom dresses,
party dresses,
evening dresses,
mother of the bride dresses,
special occasion dresses,
cheap quinceanera dresses,
hot red wedding dresses

jordan said...

I think it is a very convenience and save time way to buy goods.I often buy jordan shoes ,gucci bags,NFL Jerseys, UGG Boots, Tiffany jewelry,nike shox on the Internet.you can seach Air Jordan ,Nike Shoes to find the jordan shoes, and I also like Nike Shoes, they are good wear. Anyway,I like Tiffany jewelry best.It can make me more confident and buty.It’s really a good shopping way,if you haven’t do that,try it.You will enjoy yourself.

ripleyripley1973 said...

I really like this glasses article, and hope there can be more great resources like this.
We share the opinion on eyeglasses and I really enjoy reading your article.
Great resources of glasses online! Thank you for sharing this with us.

ripleyripley1973 said...

I really like this glasses article, and hope there can be more great resources like this.
We share the opinion on eyeglasses and I really enjoy reading your article.
Great resources of glasses online! Thank you for sharing this with us.
Good job for writing this brilliant article of prescription eyeglasses.
This is the best cheap prescription sunglasses article I have ever found on the Internet.
I totally agree with you on the point of ray ban. This is a nice article for sure.
I greatly benefit from your articles every time I read one. Thanks for the ray ban sunglasses info, it helps a lot.
Bright idea, hope there can be more useful articles about ray ban sunglasses online.
You have given us some interesting points on ray ban aviator. This is a wonderful article and surely worth reading.
I like your ideas about ray ban wayfarer and I hope in the future there can be more bright articles like this from you.
It has been long before I can find some useful articles about ray ban wayfarer sunglasses. Your views truly open my mind.
I totally agree with you on the point of brille. This is a nice article for sure.
I love this brillen article since it is one of those which truly convey useful ideas.
I appreciate your bright ideas in this brillengläser
article. Great work!
I am glad to read some fantastic optiker article like this.
Great article,it's helpful to me, and I also like the useful info about kunststoffbrille.
Excellent point here. I wish there are more and more kunststoffgläser
articles like that.
Thank you so much for sharing some great ideas of kunststoff-brille with us, they are helpful.
Bright idea, hope there can be more useful articles about gleitsichtbrille.
I like your ideas about gleitsichtbrillen and I hope in the future there can be more bright articles like this from you.
I greatly benefit from your articles every time I read one. Thanks for the retro brille info, it helps a lot.

ripleyripley1973 said...

Your do have some unique ideas here and I expect more retrobrille articles from you.
What an inspiring article you wrote! I totally like the useful retro-brille info shared in the article.
You have given us some interesting points on eyeglasses. This is a wonderful article and surely worth reading.
It has been long before I can find some useful articles about eyewear. Your views truly open my mind.
This glasses online article is definitely eye-opening and inspiring.
Your do have some unique ideas here and I expect more bifocals glasses articles from you.
This bifocals eyeglasses article is definitely eye-opening and inspiring.
I really like this progressive glasses article, and hope there can be more great resources like this.
This is the best progressive eyeglasses article I have ever found on the Internet.
Great article, it's helpful to me, and I also like the useful info about mens glasses.
I appreciate your bright ideas in this men's glasses article. Great work!
What an inspiring article you wrote! I totally like the useful mens eyeglasses info shared in the article.
Good job for writing this brilliant article of mens eyewear.
Excellent point here. I wish there are more and more men's eyewear articles like that.
We share the opinion on brillengläser
and I really enjoy reading your article.
Great resources of optiker! Thank you for sharing this with us.
I am glad to read some fantastic eyeglasses article like this.
Thank you so much for sharing some great ideas of glasses online with us, they are helpful.
I love this prescription eyeglasses article since it is one of those which truly convey useful ideas.

nike said...

The first and second Android powered smartphones that were released in the US market quad band mobile phones were respectively the T-Mobile G1 and T-Mobile myTouch 3G – both handsets were products from smartphone maker HTC. best cell phonesThen, shortly after the myTouch 3G was introduced, more and more Android handsets started pouring in, eventually beginning the Android mania we're witnessing today. China Mobile Phones Here comes the T-Mobile myTouch 3G Slide –Nike Shoes a distant relative to the first Android phone ever. Packing a physical QWERTY Cheap Cell Phones to supplement the messaging experience, it's still one of the few handsets available to T-Mobile customers Wholesale Cell Phone that run Android 2.1 right now. Moreover, it employs a slightly modified version of Sense, but will it be enough to entice customers in the midst T Mobile of an already crowded market? When you think of the many industrial designed Mobile Phone smartphones that HTC has been able to meticulously craft over the years, the myTouch line of devices have been somewhat of a departure –ed hardy swimwearand the myTouch 3G Slide follows suit. Employing an almost identical design style that's evident on the ed hardy caps, it essentially looks just like it except for the addition of a slide-out physical QWERTY. ed hardy ukCorners are rounded that make it naturally comfortable to hold in the hand, plus it has a slight chin on the upper and lower portion of the touchscreen cheap ed hardy. The handset isn't afraid to flaunt its girth as it looks considerably bulky (0.60” thick) over some contemporary models like the Motorola DROID – plus it packs some serious weightDiscount Ed Hardy (5.90 oz) despite its plastic construction. Ultimately its design definitely screams for a mid-range offering, ed hardy shoesbut we're not confident that it could withstand a drop or two – even more so when it's one heavy device. ed hardy t-shirts Traditionally, it's hard to find any

Pink Love said...

1ed hardy
ed hardy jeans
ed hardy swimwear
ed hardy hoodies
ed hardy christian audigier
ed hardy women Leggings
ed hardy long sleeve polo

2nba jerseys
nfl jerseys
mlb jerseys

nhl jerseys

Los Angeles Lakers jerseys
New York Jets jerseys

3coach bags
coach handbags
Coach Claire Bags

coach wallets coach sunglasses Coach Luggage Bags Coach HOBO Bags Coach Ergo Bags

Coach Sabrina Bags

cheap Coach Backpacks
Coach Shoulder Bags

4

ghd purple
ghd dark
ghd pure
ghd pretty in pink
rare ghd
GHD IV Styler
ghd mini styler
ghd mk4 gold styler
ghd pink

hxl said...

baby bedding
bed in a bag
sexual health
health plan
beauty cosmetics
skin care
health fitness sports
mens health
fashion shoes reviews
best air shoes
best women shoes
fashion dress
comfortable man shoes
fashion shoes
sneakers reviews
top ten boots
boots of world
rosetta stone
boots classic
wholesale lots
china wholesaler
china wholesale
wedding dress
lightinthebox reviews
fashion shoes

健康365

加拿大营养屋

健康药品大全

健康365

欣乐佳

中食月太

Air Max Nike said...

Nike Air Max
Air Max Nike
Air Max Shoe
Wholesale Nike Air Max 2009
air max 2009
Nike Air Max 2009
Cheap Nike Air Max
air max 90
Nike Air Max Shoes

Air Max Nike said...

welcome to Greenreplica.com,it provided Lots of low price but high quality including Nike Air Max,Air Max Shoes,Air Max 90,Nike Air Max Shoes,Cheap Nike Air Max,Air Max Nike,Wholesale Nike Air Max 2009,we have thousands of Nike Air Max and Air Max Shoes Wholesale.

tn requin said...

sleeping bag
tablecloth
travel luggage
car gps
car parts
GPS navigation
portable GPS
lcd tv
flat tv
digital picture frames
unlocked cell phones
wedding dresses
wedding jewelry
chaussures mode
chaussures Femmes
women's shoes
round tablecloth
discount handbags
chaussures sport
chaussures pas cher
fashion bedding
id lanyard
lanyard
creative gadgets
gift ideas
kids wall stickers
wall stickers
bath curtains
kitchen faucet
bathroom faucet

Air Max Nike said...

Nike Air Max
Air Max Nike
Air Max Shoe
Wholesale Nike Air Max 2009
air max 2009
Nike Air Max 2009
Cheap Nike Air Max
air max 90
Nike Air Max Shoes
nike air max 24-7
nike air max 2010
wholesale air max 24-7

Air Max Nike said...

Nike Air Max
Air Max Nike
Air Max Shoes
Wholesale Nike Air Max 2009
air max 2009
Nike Air Max 2009
Cheap Nike Air Max
air max 90
Nike Air Max Shoes
nike air max 24-7
nike air max 2010
wholesale air max 24-7

jack cark said...

Nike Shoes

UGG Classic Tall Chocolate

UGG Bailey Button Boots

dfadf said...

The Tax Return Crack-Up<2>
I was not shocked because this was old news -- practically ancient, in fact. In R. Microsoft Office Emmett Tyrrell, Office 2010 Jr.'s most recent book The Clinton Microsoft Office 2010 Crack-
Up, page fiv Office 2007 e, paragraph two, we learn that in Bill Clinton's "first four years out of the White H Microsoft Office 2007 ouse, he ea Office 2010 key rned over Office 2010 download $43 million Office 2010 Professional after
expenses... Microsoft outlook "
The next Outlook 2010 page directs Windows 7 us to Appendix Microsoft outlook 2010 I, a list of the conniving couple's fees for speeches and book royalties and other income. The first

elizabeth bernot said...

Costa Rica Fishing

http://www.fishingcostaricaexperts.com/

Fishing Costa Rica