Camera movement = bad render?

mark30 wrote on 3/2/2003, 4:23 AM

Hi everyone,

Does anybody know what causes the problem of certain clips in which the camera pans give render with horizontal, kind of flickering lines? If I play them it seems fine, but as soon as I start to render it comes out with these annoying horizontal lines. I tried to change field order etc. but I can't get it to work right. I'm using VV3. rest of the material renders perfectly...

grtz,
Mark

Comments

TorS wrote on 3/2/2003, 9:25 AM

Interesting thought! Panning must be what digital video cameras are worst at. I guess it's something to do with the way they "draw" the images, put up against the way they compress the data. It would not surprise me to hear that the rendering process is able to increase the bad end of that compromise. Can someone shed light on this - in a straight shot with no panning?
Tor

DDogg wrote on 3/2/2003, 1:12 PM

To understand it you would have to do some web research on how video compression is done. Pans, and to some extent zooms are the worst possible senario for video compression.

To get you started and in a way too generalized way, video compression establishes a key frame and then the following frames are just stored as the difference between the key frame. A simple example is the standard talking head shot. The background and much of the rest of the frame is not changing much so the frames after the keyframe need only store the changes in the face (again, way to generalized). Pans, by their nature, cause havoc because every frame is different and every frame must use the full available bandwidth to store a full version of each frame. You can see then why pans can be problematic in any video compression format.

Very slow pans with good lighting should hold up ok in DV as it is only a 5 to 1 compression if memory serves me. Fast pans, especially with bad lighting are gonna kill you.

TorS wrote on 3/2/2003, 1:38 PM

That - to me - looks like a good explanation of something possibly very complicated. And however simplified it may be - it is a good argument for avoiding pans and zooms - which generally don't add anything good to a production anyway. I said generally.
Tor

Former user wrote on 3/2/2003, 2:11 PM

This might be normal TV interlacing. Are you watching the video on computer or TV? what compression/codec are you using? If you output to tape, do you see the lines?

Dave T2

mark30 wrote on 3/3/2003, 11:58 AM

I do think the interlacing is not the prob here. I see the lines when I 'render to new track' but also printing to tape and viewing on tv. It's just digibeta material --> DV --> firewire in pc. And firewire back of course. Thing is that the rest of the material looks great. It's just the panned shots that suck. They look ok on the Vegas preview though.

I guess I'm just gonna make an edit avoiding the bad parts.. And tell everyone not to pan anymore :)
Thank a lot guys!
Mark

Former user wrote on 3/3/2003, 12:53 PM

Are you rendering at BEST or GOOD? I found some weird artifacts when I resize at GOOD, so I always use best.

Dave T2

mark30 wrote on 3/4/2003, 1:37 PM

Hi Dave,

I always render BEST. Have to, 'cause almost everything I make is for TV broadcast (in the Netherlands)
I replaced the bad parts in a lineair editsuite to get this thing broadcast, but I WILL figure out what has been the problem. Thanks again everyone..

Will post a new question concerning field skipping.. getting that cool filmy effect. Does anyone know how to do that?
thx

Erk wrote on 3/4/2003, 1:56 PM

Would the video supersampling in V 4 help any here, maybe soften up that pan a bit? I haven't explored that feature yet.

G