MPEG 2 artifacts on Pan/Tilt

PeterWright wrote on 8/28/2006, 12:09 AM
I'm working on some footage shot on Digibeta then transferred to Mini DV before capture.

Generally looks more than fine, but after encoding for DVD using the DVDA PAL widescreen template (Best quality) there are slight horizontal wavy line artifacts when the camera was panned or tilted.

I'd appreciate tips to reduce or get rid of this - Bitrate? CBR? Two Pass? - no problem with space - DVD will only be 10 mins.

Comments

farss wrote on 8/28/2006, 12:31 AM
Are you certain this wasn't in the source?

8Mb/sec CBR is about as high as you can safely go and you'll easily fit 10 minutes of that onto DVD. However this doesn't sound like a mpeg-2 encoding issue.

One trick I've used with problem sections which weren't really just encoding issues was to add a little GB to the problem section, reducing the resolution and hence the stress level of the encoder can help.
PeterWright wrote on 8/28/2006, 12:33 AM
Thanks Bob - no , definitely not in the avi - BUT - a bell has just rung - for some reason there were black lines at the sides after the Digibeta / MiniDV transfer, and to get rid of them I edged in a little Pan crop - maybe I've induced the problem by playing with fields ... back to testing .....
farss wrote on 8/28/2006, 3:22 AM
That'll do it for sure!

Probably better to just add a tiny even black border to mask it.

Otherwise check your de-interlace method.
PeterWright wrote on 8/28/2006, 5:31 AM
Well getting rid of the Pan/Crop has helped, but there are still a few residuals - when you say de-interlace method, Bob - I haven't knowingly applied any - certainly the avis are "None" - are you referring to the MPEG encoding?
farss wrote on 8/28/2006, 7:01 AM
If you're not doing anything to the image then the de-interlace method as defined in project setting has no effect however it seems that they do have an impact when scaling the image.

All that aside horizontal line can look wierd in interlaced video and the effect only shows up on an interlaced display.

Consider a near horizontal line. Part of it appears in say one line of say the lower field and the other part appears in a different line of the upper field. No problem so far. But if the camera / object moves then parts of the line are jumping between fields. This is most noticable on footage from hi res cameras, more so on HD downscaled to SD. Worst example would be striped clothing. Used to be if you turned up at a TV station with TV unfriendly clothes you got sent to wardrobe, these days I doubt they worry.

Bob.
PeterWright wrote on 8/29/2006, 2:57 AM
Well, happy to say I met the deadline today with a "beaut" looking DVD - but learnt an important lesson.

Just about all the horizontal artifacts were caused by my slight Pan/Crop to get rid of black lines either side of frame from the Digibeta/Mini DV dub. Once I put everything back to how it was, those horrible shaky lines disappeared. It wasn't just on camera movement either - with close ups, even moving lips created artifacts. The point is that the black lines are not visible, even on a modern widescreen plasma TV, so I should not have worried about them - those folks who choose to view on PC will see them, but hardly noticeable.

The only exception was one shot with a lot of camera pan, when even removing Pan/Crop did not remove the artifacts - then I remembered I had been encoding from a second generation render - when I put the original Mini DV dub footage there to be encoded to MPEG2, all was fine - I guess I could have used nested projects, but I used Ctrl C/Ctrl V to transfer the original from one project to another and all is well - time for a beer ..............