Compression artifact problem at DVinfo.net

Neil Boone · January 16th, 2007, 01:26 PM

I made a funny little glitch sequence that has some noise and distorted still frames that blend into one another in less than two seconds, like a taped over spot on a home movie look, and when the next 'clean' shot of the sequence comes up after the glitch effect it goes real crazy boxy-artifact looking on me in the final mpeg2 (CBR 8.5, motion est. Best) for about 2 sec. following the effect. I've tried setting compression markers before and after the cut , maybe 10-12 total, and other various methods, including a 1-pass VBR version, with no complete solution. I've reduced the artifacting but not eliminated it. It still wants to be there. Any ideas how to have it compress correctly? I've never even seen this before.

John Miller · January 16th, 2007, 01:35 PM

That's the fundamental weakness of MPEG2-variant editing.

What you need to do is align the first clean frame (after the 'glitch' effect) with the I-frame of an MPEG2 group of pictures (GOP).

One way to achieve that is to make the glitch effect last a few frames longer (or shorter)...

I'm sure others may be able to advise if it is possible to control when an I frame is generated by your software.

Neil Boone · January 16th, 2007, 03:23 PM

I should have thought of that. Good call, I'll cut it by a couple frames and recompress, funny I've never hit the wrng frame before after all these years. The compression markers did help though it seemed.

Neil Boone · January 16th, 2007, 04:17 PM

So I tried moving the cut some on the timeline, first by about 2 frames backwards into the glitch with no change. Then I went to the head of the program and extended the color bars by an extra 7 frames (so now +5 frames ahead of original spot) with no change. Now I'll try moving bars more than 15 frames ahead and see what i get.

Neil Boone · January 16th, 2007, 04:43 PM

I've even tried adjusting the in point of the actual first 'clean frame' and moved the whole sequence 2+ seconds forward and still i get artifacts on that cut. Any other ideas what this could be? I need to figure this out as I don't know why this would happen and have to make playback DVD's for television that can't have pixelation. Any ideas are greatly appreciated. I thought the I frame thing would work but not yet, where is the I frame determined? In my actual footage or can i change it on my timeline as i've tried now a few times?

January 16th, 2007, 01:26 PM	#1
Neil Boone New Boot Join Date: Sep 2006 Location: Wilmington, NC Posts: 19	Compression artifact problem I made a funny little glitch sequence that has some noise and distorted still frames that blend into one another in less than two seconds, like a taped over spot on a home movie look, and when the next 'clean' shot of the sequence comes up after the glitch effect it goes real crazy boxy-artifact looking on me in the final mpeg2 (CBR 8.5, motion est. Best) for about 2 sec. following the effect. I've tried setting compression markers before and after the cut , maybe 10-12 total, and other various methods, including a 1-pass VBR version, with no complete solution. I've reduced the artifacting but not eliminated it. It still wants to be there. Any ideas how to have it compress correctly? I've never even seen this before.

January 16th, 2007, 03:23 PM	#3
Neil Boone New Boot Join Date: Sep 2006 Location: Wilmington, NC Posts: 19	Aha I should have thought of that. Good call, I'll cut it by a couple frames and recompress, funny I've never hit the wrng frame before after all these years. The compression markers did help though it seemed.

January 16th, 2007, 04:17 PM	#4
Neil Boone New Boot Join Date: Sep 2006 Location: Wilmington, NC Posts: 19	tried it So I tried moving the cut some on the timeline, first by about 2 frames backwards into the glitch with no change. Then I went to the head of the program and extended the color bars by an extra 7 frames (so now +5 frames ahead of original spot) with no change. Now I'll try moving bars more than 15 frames ahead and see what i get.

January 16th, 2007, 04:43 PM	#5
Neil Boone New Boot Join Date: Sep 2006 Location: Wilmington, NC Posts: 19	no luck I've even tried adjusting the in point of the actual first 'clean frame' and moved the whole sequence 2+ seconds forward and still i get artifacts on that cut. Any other ideas what this could be? I need to figure this out as I don't know why this would happen and have to make playback DVD's for television that can't have pixelation. Any ideas are greatly appreciated. I thought the I frame thing would work but not yet, where is the I frame determined? In my actual footage or can i change it on my timeline as i've tried now a few times?

January 16th, 2007, 01:35 PM	#2
John Miller Major Player Join Date: Oct 2005 Location: Hillsborough, NC, USA Posts: 968	That's the fundamental weakness of MPEG2-variant editing. What you need to do is align the first clean frame (after the 'glitch' effect) with the I-frame of an MPEG2 group of pictures (GOP). One way to achieve that is to make the glitch effect last a few frames longer (or shorter)... I'm sure others may be able to advise if it is possible to control when an I frame is generated by your software.