Quirky Pixelation Problem

[Mike Prendergast]

I'm experiencing a frustrating problem with a rendered video. Source files are mp4 and avi (1280x720, 60 fps). I convert the camera mp4 to avi with Cineform Neoscene. The resulting rendered file (mp4, 640x360, 30 fps) has two brief (one second or so) sections where the pixelation occurs, nearly full screen. I have checked the time-line for issues and see nothing to indicate what the problem is. To make matters even stranger, when i move the clip with the pixelation to the right and extent the clip on its left the pixelation appears in the same place on the time-line not in the same image. The pixelation doesn't appear in preview only in the rendered file. And when i render to 1280x720, 30 fps (same mp4 type) the pixelation does NOT appear in the rendered file. Any clues? Is there maybe something corrupt in the time-line? Can i move everything (in one step) to a new project? It is a very complex time-line and reproducing it from scratch will be a nightmare.

Rendered file is here:

USA Pro Cycling Challenge Stage 2 Review Ride on Vimeo

jump to 17:12 and 17:32 for offending pixelation.

[Adam Stanislav]

Originally Posted by Mike Prendergast

I convert the camera mp4 to avi with Cineform Neoscene.

Why? Vegas can read mp4, can’t it. So what is the reason to change it to a different format?

[Mike Prendergast]

Hi Adam, I have found the avi files reduce choppy playback that happens when mp4 files are used directly.

[Adam Stanislav]

Playback while you’re editing, or while you watch the rendered video after you have finished editing?

[Mike Prendergast]

Adam, the playback when editing. by "used directly" i meant used on the timeline and then viewed inside VMS as part of the editing process.

[Adam Stanislav]

OK. Personally, I’d rather put up with that than risk introducing any artifacts to the image. I have never used the Cinerform Neoscene codec, even though many people swear by it. My problem with it is that it decompresses the video, then manipulates it, then recompresses it again.

The only intermediary codec I would be willing to use is one that uses guaranteed non-lossy compression. Decompressing and recompressing with a lossy compression is almost guaranteed to lower the quality of the image. And, according to their web site, they interpolate 4:2:0 to 4:2:2 which sounds like they are improving the source. They are not improving it, they are only increasing the chance of introducing additional artifacts.

If you are experiencing some pixelation, that may actually be a byproduct of converting the image from one lossy format to another. I would definitely try replacing your AVI files with the original mp4 files, even just for a small segment to test, and see if you still experience the pixelation. If not, it was introduced by using the intermediate codec. Otherwise, the problem is somewhere else, but at least you will have eliminated one suspect.

[Mike Prendergast]

Adam, Thanks for the followup. I tried your suggestion and used the mp4 file for the clip. The problem is still there. Is it possible to move my entire timeline to a new project? Maybe something is corrupt in project file that i can't fix.

[Adam Stanislav]

Doing the same thing is likely to produce the same result. But Vegas has a way to export everything into a text file instead of a .veg file (Save As... EDL text file), which you can presumably import into another project (Open... EDL Text File). I have never experimented with it, though, so I am not really sure whether it works smoothly.

What I would do next is select just the few seconds where it happens and render just the selected area into an uncompressed AVI file and see if the problem persists there. If not, whatever codec you have used to render the full project is the culprit. If yes, the problem is either with the original source or whatever processing you are doing to do it.

[Mike Prendergast]

Thanks for hanging in here with me on this problem. I really need to solve this. I did try your avi suggestion just now. The uncompressed avi doesn't have the pixelation. However...

When i render to a Sony AVC mp4 file, 1280x720 the file looks fine, no pixelation issues. When rendered to Sony AVC mp4, 640x360 i see the pixelation.

[Adam Stanislav]

Now we’re getting somewhere! Do not use Sony AVC, use MainConcept AVC. Either that, or use HandBrake to produce the 640x360 from the 1280x720. But I would go with the MainConcept AVC first. It does a much better job than Sony AVC. In fact, I wish Sony would just drop the Sony AVC from the options altogether.

[Mike Prendergast]

Thanks for the Main Concepts tip. I think that worked. I rendered the offending area and it worked. i'm doing the entire project now. Do you have any recommended parameters to use, such as bps? I set it to avg = 2,000,000 and max of 4,000,000 for 640x360 and will try double that for 1280x720. There no pre-sets for main concept in VMSHD 10.

[Adam Stanislav]

The BPS really depends on what you need it for. The higher the BPS, the better the quality but also the larger the file.

[Mike Prendergast]

Thanks for your help and solution Adam. The Main Concepts render worked well. I really appreciate your effort on this.

[Mike Prendergast]

Originally Posted by Adam Stanislav

The BPS really depends on what you need it for. The higher the BPS, the better the quality but also the larger the file.

I'm posting the video on vimeo and the values i picked, 2-4 MB/s and 4-10 MB/s, seem to work. I just don't know how to choose for quality vs bandwidth. I think vimeo has some info on that. i'll check but if you have any thoughts please let me know.

[Adam Stanislav]

I believe Edward Troxel has some kind of a bit rate calculator somewhere on his web site. He is a regular here, so he will probably answer that question better than me.