Pixelation from numerous mpeg conversions

jdubya · Post by **jdubya** » Thu Jun 02, 2005 6:37 am

Hi,
I started having some pixelation show up in a dvd project and I'm wondering if maybe I have rendered the mpeg too many times.I captured the original video from vhs in mpeg 2 format using dvd express and I must have "created video" 11 times since last fall to ntsc dvd.I like to see my progress and how different effects look on tv so while I've been learning more and more I've just read on this board that you should only render to mpeg once.I only noticed this pixelation around titles and in some of the video.Never happened before.These are my properties which have varied slightly since I started:File format: ntsc-dvd, upperfield 1st,24 bits, 720x480, 4:3
Data rate:Variable: 3999 at first then 6000 twice and back to 3999
Audio: dolby dig now but when I started it was mpeg audio layer2.
I have changed the field order, before I learned not too, but that has never seemed to affect the quality.I'm working with old 8mm film from the 50's,60's that was copied to vhs so the overall quality isn't great in some spots because of age and whatnot.My question is: If I transfer the original video from the vhs again can I still use my acquired vsp files so I don't have to manually go along and recut everything and therefore erase my mistakes ? TIA

jchunter · Post by **jchunter** » Thu Jun 02, 2005 3:47 pm

My tests have shown that at a video bitrate of 8Mbps, there is no discernible loss of resolution in Mpeg2 after 10 consecutive edits an rerenderings. Coalman saw visible compression artifacts below a bitrate of 6Mbps.

In your case, you started with analog VHS tapes, which are significantly lower in resolution than digital video. Upper field first is the correct field order. If you rendered to Lower Field First, you probably reduced resolution but may not have noticed it at the time. It could have left some degradation. Changing it back could have also reduced resolution. Increasing the bitrate to 6Mbps on video captured at 4 Mbps can not improve resolution but might reduce compression artifacts when rerendering.

If you recapture the original video, you will have to re-edit them in a new project.
John

DVDDoug · Post by **DVDDoug** » Thu Jun 02, 2005 6:07 pm

My tests have shown that at a video bitrate of 8Mbps, there is no discernible loss of resolution in Mpeg2 after 10 consecutive edits an rerenderings.

Wow! I haven't done any scientific experiments, but I'm pretty sure that I saw deterioration after one re-code of an MPEG (I don't recall the bitrate).

I am 100% sure that I get huge pixels when crossfading from one MPEG to another. Of course that only happens during the crossfade as the majority of the file does not require recoding.

jdubya · Post by **jdubya** » Thu Jun 02, 2005 7:10 pm

Well, jchunter, I was afraid I might have to recut and title but before I do I'm gonna try using the original captured movie and see what happens.I can't lose anything.Cutting up and fitting music to these old clips is a time consuming task as you probably already know.Thanks for your attention.

kebrinton · Post by **kebrinton** » Thu Jun 02, 2005 11:53 pm

jdubya --

If you still have the original captured material, you have all you need. None of your editings has changed THAT. The changes are saved in the little .VSP project files and implemented only when you Create new video file -- without changing the original footage.

Keith