jitter problem with Vegas MPEG-2 encoder

trock wrote on 3/30/2005, 7:15 AM

I really like the Vegas MPEG-2 encoder but I have a recurring problem that has been forcing me to frameserve to an external encoder and I wondered if there is an internal settings solution.

Basically all looks fine except when there is a fade to black followed by a fade-in that has some motion going on during and/or immediately after the fade-in. The result after the Vegas encode is jittery. This is at Q31, 1 or 2 pass.

If I frameserve to TMPGEnc XP3 and encode either 1 or 2 pass the result is perfect with no jitter.

Is there any setting in the Vegas encoder that may reduce this motion jitter after a fade-in?

Thanks,

Tony

Comments

craftech wrote on 3/30/2005, 7:31 AM

We need more details. Are you authoring with DVDA when the problem occurs? Which version if you are?
What "field order" are you using in Vegas?. I am assuming that it occurs in a fade over Video and not over a still.

John

trock wrote on 3/30/2005, 1:33 PM

Thanks John. I'm authoring in DVD-Lab but the problem occurs before the authoring and is in the mpeg-2 encoding - which I'm doing in Vegas. If I frameserve out to a different encoder the problem is not there. It's DV so I'm using bottom field first. And yes, it occurs in a fade-in over video.

Tony

farss wrote on 3/30/2005, 2:06 PM

Fades over motion are a real problem for encoders (every pixel changes value between every frame), perhaps TMPGs encoder handles the problem better, what bitrate are you encoding at?
Bob.

trock wrote on 3/30/2005, 2:42 PM

Hi Bob. It's a 1.5 hr project and I'm encoding at 6000 as the average.

Tony

farss wrote on 3/30/2005, 3:14 PM

So the encoder should be able to cope at that birate, particularly witha 2 pass encode. I've noticed the same thing at times with dissolves between clips where both have lots of motion (try dissolving between two fast pans!).
Only two ways I can think of to deal with this, change the video that's causing the problem or use the tool that does the job. I've changed dissolves/fades into cuts at times because of this issue but it's only affected me at lower bitrates. You could add blur to the video during the fade up to reduce the required bitrate but if TMPG encodes correctly why not just use that?

trock wrote on 3/30/2005, 4:06 PM

Thanks Bob. I do end up having to use TMPGEnc but I prefer the speed of the Vegas encoder, especially when I'm doing 4-DVD projects with 8 hours of footage and want to minimize encoding time. In all other respects the Vegas encoder works really well.

farss wrote on 3/30/2005, 4:13 PM

Also I think the TNPG encoder does some degree of noise reduction, you can certainly dial in some in the Advanced preferences. I've run into nasty problems with noise and mpeg-2. It encoded just fine but I had a fade up from absolute black into an in camera iris up which was obviously full of noise. Some players would spit the dummy and stop at that point, looking at the mpeg stream using BitRate Viewer I could see the bitrate go from next to nothing to 8.5MB/sec in the space of a few frames. Lots of technical stuff elsewhere about why this spins out players. Replaced the in camera fade up completely and all was well.
Bob.

trock wrote on 3/30/2005, 4:48 PM

I was hoping that there might be a setting somewhere in the Vegas encoder that would reduce or eliminate the post fade jitter, but I guess not. It looks like my main options are to continue to use TMPG (which only does NR if you ask it to, btw) or change all the offending section title fades to cuts. Thanks for the feedback. At least I'm not the only one who's run into this :)