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View Full Version : What causes video tearing



Ian-T
11-13-2009, 09:05 PM
I believe this topic has been touched upon before but I can't find it. But from what I remembered there were some folks who suggested that the tearing we see in our playback device onscreen is probably caused by a slow reading video card etc. The tearing I'm talking about happens mostly when the footage is panning from left to right. It creates a sort of rip accross the screen until the panning stops and I hate it.

My thoughts is it has more to do than just a slow video card. I say this because I watch a lot of HD footage from Apple Trailers and I don't see it in their 720p and 1080p footage. It's usually from footage that the average folks shot on their camcorder and uploaded. But not theatrical trailers. SO, what do you all think it is? The original codec used? Do any of you see the same thing I'm talking about?

ydgmdlu
11-13-2009, 09:14 PM
It's the codec. H.264 is very resource-intensive to decode, more than just about any other commonly used codec.

Ian-T
11-14-2009, 08:03 AM
vdgmdlu I know that thanks. But what I'm talking about is footage that was encoded for Web viewing (H.264 @ maybe around 8-10 Mbps). As I mentioned earlier when viewing downloaded trailers from online I notice they are encoded exactly the same as some folks footage (H.264 at the above data rate) but there is usually no evidence of tearing in those clips when panning etc. What's the difference?

Barry_Green
11-14-2009, 08:07 AM
Tearing is probably due to the scan rate of your monitor. Try upping the refresh rate to the fastest possible speed and see if you don't notice a significant improvement. Even drop down to a lower resolution for the purposes of testing, so you can get the scan rate faster.

Tim Joy
11-14-2009, 08:17 AM
I just got a 1920x1080 monitor and I'm a bit disappointed at the tearing when viewing full screen. It makes the footage look strobey and jumpy when it's not. Viewed at 1/4 size it is fine.

I don't seem to have any options for refresh rate than 60hz. :(

i wonder about the response time. It seems that most of the monitors were 5ms. Is that slow?

xbourque
11-14-2009, 09:21 AM
The problem is not refresh rate. I bet most modern monitors do not go below 60hz anyways. And most LCDs don't have any way to change the refresh rate.

The problem is that the player software isn't syncing the playback to the refresh rate of the monitor, switching frames when the monitor is halfway done scanning the image.

FWIW QuickTime Pro on my Macbook seems to be playing back "genlock" to my monitor, but embedded Vimeo clips aren't.

-X

ydgmdlu
11-14-2009, 11:36 AM
vdgmdlu I know that thanks. But what I'm talking about is footage that was encoded for Web viewing (H.264 @ maybe around 8-10 Mbps). As I mentioned earlier when viewing downloaded trailers from online I notice they are encoded exactly the same as some folks footage (H.264 at the above data rate) but there is usually no evidence of tearing in those clips when panning etc. What's the difference?
OK, if you really want to go there... My guess would be the playback software and the way that it interfaces with your video card. There are multiple ways to render video on a computer. (I'm referring to rendering in the playback sense, not in the editing/post-production sense.) On Windows, there's the Overlay Mixer, VMR7, VMR9, and more. Each of these has a different effect on playback quality and performance. If different playback software use different methods, then you might see the different results like you're describing.

bwwd
11-14-2009, 05:27 PM
I see the tearing on 7D too when i dont even recording so does 7D has refresh rate not really fast enough for 24 and 25p ?
---
Changing video generator in my player to Overlay helped.I have only 60hz too in my old laptop.

denzlite
04-30-2010, 02:17 PM
I'm replying to this older thread because I'm having the same issues with the footage I shot on my first day with the t2i.

Clip from the first test shots:
http://vimeo.com/11364697

Can anyone confirm there's a bunch of frak in this clip so I can rule out my other factors as the culprit and so I don't frakin shoot myself.

First of all, I've encoded these clips every conceivable way.

A. I thought that all the noise/tearing/lines were due to the fact that I encoded with H.264 at too high a bit rate. But with every bit rate/size I see the same thing. This clip is down/resed to 720 but it looks identical to the 1080p clips I uploaded.

A part 2 > No matter what version I encode to h.264 (canon mov, avid codec, photojepeg) I get the same results.

B. I upgraded my video card thinking that my onboard video was not up to par. See the exact same issues. Was also hoping that a dedicated video card would improve performance in Prem CS4. Sigh, maybe a slight edge, but Perm just can't deal with the raw canon or avid footage on my box running quad core.

C. These clips were shot with a Canon 1.8 50mm II lens. Could it be that the shutter speed is just plain off or that the lens itself just cannot handle sudden movements?

Any help appreciated.

deltoidjohn
04-30-2010, 07:16 PM
I don't understand what you mean by 'tearing' or 'frak' but there are a few things I can see going on in this clip:

1. Unsteady footage. This makes it harder for inter-frame codecs such as h.264 to resolve detail becasue there are so many changes in each frame.
2. Fast movements, pans, and general shakiness expose the jerky nature of 24p footage. A slower shutter speed will help to a degree by blurring some of the stuttering but the fact is that 24p cannot handle fast motion very well.
3. Rolling shutter is causing skew. In the shot of the train doors, for example, the rolling shutter means the top of the image is recorded before the bottom of the image with the result being that otherwise straight lines of the moving door appear bent or skewed.

I didn't see anything out of the ordinary or anything that I would not expect to see in that kind of hand held footage. If you spend plenty of time practising steady hand-holding or if you invest in some kind of stabiliser rig and focus on smooth, slow camera movements you will likely see all of these problems dissappear.

denzlite
05-01-2010, 07:54 PM
Thanks so much djohn. Very detailed information is very helpful to me as I try to learn how to use this camera. I do need to practice much more before I go on a shoot again. Maybe using the 720p 60fps would help in the short term?

As far as the shutter speed, I'm quoting Barry Green here:


Use 1/60th in the USA, or 1/50th in PAL territories. NEVER EVER EVER use 1/250th, 1/500th, or anything like that.I think for now, that's the way to go until I understand the limitations of the camera better.

http://dvxuser.com/V6/showthread.php?t=208745&highlight=shutter+speed


I see here also that you say:


I use shutter speeds upwards of 1/50th all the time. When shooting surfing at 50p I will go up to 1/1000th on occasions. Otherwise you end up with blurry crap with no detail.

I agree that dealing in absolutes is not a good idea. Yes, the 180 degree shutter rule is the standard because of the right balance between stobiness/motion blur blah blah blah but there are times when the situation calls for a different shutter speed.

I do however, agree that people need to make themselves more aware of how their camera will behave with different settings and how to work around different problems. And in this scenario, it seems like sticking to 1/50th (or 1/60th) is the easy solution. I just watched Amores Perros again. I'd like to get that kind of hand held effect. I agree that a good stabilizer and practice would help. I'm wondering how much the camera he was using in that weighed.