B-frames explanation

dornier wrote on 11/19/2006, 6:18 AM
Has anyone a link to a good discussion on B-frame settings for rendering out to mpg-2?

I've been working on an animated short that is clean and crisp in design. However, after rendering out to mpg-2 for DVD setup I notice trace edges (for lack of a better word) similiar to outside edges when premultiplying alpha channels.

It's very subtle but it's enough to almost give the sense of a slight shadow or motion blur on the edge of moving elements--even elements far from the edge of the image (not the egdge of a straight matte).

I'm just curious if there are settings within Vegas that might affect this.

Thanks in advance folks.

jim

Comments

ScottW wrote on 11/19/2006, 6:51 AM
http://www.mpeg.org/MPEG/starting-points.html

Since I-Frames are complete frames, one thing you may try is setting the I-Frame count to 1 and the B-frame count to zero on the video tab in the customize dialog for render as. That will give you nothing but I frames - if you still see the visual issue then you know the problem is likely not with the MPEG encoding.

--Scott
dornier wrote on 11/19/2006, 7:22 AM
Thanks Scott, since I've already got one the old way. I can just crank out a new one and compare.

(to be continued)
dornier wrote on 11/19/2006, 10:15 AM
Well, the I-15, B-0 came out terribly. Very grainy with a lot of jitter.

I've noticed there are to NTSC templates for 720 x 480; one for DVDA and one for everyone else.

Do you think there is something specific to the DVDA template that makes the cartoon images not as dull?

farss wrote on 11/19/2006, 11:13 AM
Animation usually compresses very well. Perhaps your problem isn't due to the mpeg-2 compression. Out of gamut colors or rapid changes in chroma phase on adjoining colors within a frame could be the cause of these problems.
Is the source material a stills sequence, the footage hasn't been through DV25 compression as well has it.
dornier wrote on 11/19/2006, 12:10 PM
The footage was done in Anime Studio, a 2D platform formerly known as Moho.

It was rendered out: 720 x 480 (although their default for NTSC is 720 x 540), full uncompressed AVI, 24fps.

I ran g-spot on the end-result avi and it only showed AVI, no compression.

I was thinking there might be something in Vegas preset to try to adjust the colors? Someone had mentioned "legalize"? Not sure yet.

There is a checkbox during export for "NTSC safe colors", and I have a render going right now to test that out and see if it has any affect.
apit34356 wrote on 11/19/2006, 12:39 PM
First, try encoding mpeg2 at 24p and review output. Does this look better? Second, turn off the motion blur filter on the track, re-encode.
dornier wrote on 11/19/2006, 2:12 PM
Okay, help me with that.

I don't recall motion blur on the track, nor have I ever had the need to select any other p or i settings. Where am I looking?

(btw, i'll be looking until you get back to me)
ScottW wrote on 11/19/2006, 2:25 PM
The reason they do 720x540 is because of the PAR - go back to their default. Then when you bring the media into Vegas, right click on it and clear the "maintain aspect ratio" checkbox.
dornier wrote on 11/19/2006, 3:13 PM
You mean square -v- rectangular pixels?

ScottW wrote on 11/19/2006, 4:02 PM
Yes. Your animation software is most likely designed around square pixels, my limited experience has been that outputing a square pixel source as 720x540 usually looks better in NTSC than 720x480.

Can't hurt to try.

--Scott

p.s. I said set the I-frame count to 1, not 15, if you set it to 15 with B as zero you most likely ended up with I and P frames, not just I frames.
dornier wrote on 11/19/2006, 5:13 PM
yeah, i didn't mean 1. I was looking at the default when I wrote that. 15 & 2 are showing as defaults.

As soon as this thing gets done I'll see what it comes out as. I'll try to segments also--color corrected and not.