recompression jaggies

David Thiel wrote on 6/24/2008, 1:11 PM
I am starting with an mpg file from Replay. If I look at the source file full screen it looks OK (using either Windows Media Player or Media Player Classic).
When I make a DVD DVArch recompresses it mildly (80% of original).
The result looks like this:
http://groups.msn.com/RocksAndRoses/woodworking.msnw?action=ShowPhoto&PhotoID=91

This text is static so interlace should not be a cause of the artifact. The jaggies are consistent throught the entire 120 minutes.

I use Replay mpg files on another machine with DVArch and I get good results, so it is something on this machine which is creating the jaggies when I recompress.

I tried small files that didn't require recompression and there were no artifacts so I believe that DVArch recompression is doing this.

I cannot find any options that refer to the codec or it's params.

Any ideas?

thanks in advance
DVArch 4.5 running on an intel quad core, XP, 3.5G of memory

david

Comments

bStro wrote on 6/24/2008, 4:33 PM
Have you tried a different player app on that same computer or tested this on a standalone DVD player?

I ask 'cause I suspect the playback device may be the issue, not the files. Especially if you're using the same type of source files on different computers -- DVD Architect is going to use the exact same encoder on both computers, so there shouldn't be any change there.

I agree, it's probably not interlacing. Though not for the reason you gave -- interlacing can cause a problem for static text, too. But 1) Your color combinations shouldn't make interlacing stand out that much, and 2) You're using a nice, thick font with no thin lines. Also, Interlacing usually causes a problem more with the vertical edges than the horizontal ones. Your results almost look like interference of some kind.

All that said, is there perhaps anything you can do so your Replay files don't even need to be re-compressed by DVD Architect? I think that'd be the best route, avoid re-compression altogether. Is it the source file's properties or size that requires re-compression? You should be able to get 120 minutes on a DVD if you can set your Replay's bitrate accordingly.

Rob
John_Cline wrote on 6/24/2008, 5:28 PM
It looks like there is some chroma sampling error. Instead of having DVD Architect completely recompress the file, perhaps you should use a utility that requantizes the B & P frames reducing their size without actually going through an entire decompress/compress cycle. There are several free utilities available, this is the one I found doing a quick search at videohelp.com:

http://www.videohelp.com/tools/ReJig
Here is the tutorial for using it:
http://forum.videohelp.com/topic272427.html

Here's another utility:

http://www.videohelp.com/tools/ReMPEG
musicvid10 wrote on 6/24/2008, 8:23 PM
What are the pixel dimensions of your original file?
I know nothing about Replay, but the look of your screen grab is not inconsistent with that of video upscaled to 720x480 from a smaller resolution.
David Thiel wrote on 6/25/2008, 9:33 AM
the pixel dimensions of the original file are 720x480

Let me state that I have used DVDArch to make more than a hundred disks on a different machine with other files that I transferred from this DVR. So DVDArch can recompress these files on that machine.

The DVDArch install is on a newer quad processor machine that I am trying to move my apps to.

So far this is a deal breaker.

The screen grab looks a bit wierd because it is a camera shooting the screen. Alt/PrtScrn just grabs black so I took a picture. It is a bit wierd but portrays the artifacts faithfully.

david
David Thiel wrote on 6/25/2008, 9:42 AM
I have tried Media Player and Media Player Classic, plus I have played the resulting disk in two different DVD players and the artifacts are always there.

You are right, I could set Replay image quality and avoid recompression. I'd rather not do this for two reasons.
a - It is already at medium compression which is at about the same level of artifacts as the Comcast signal I am capturing.
b - We watch the captured stream from Replay most of the time and I don't want to go any lower on image quality.

Basically I am caching shows on DVD so that I can clean up the DVR's disk.

Back to the problem, it is very regular on the horizontal scan lines as if every so many pixels are shifted up and down.

I believe that it is happening on all the horizontal lines it is just most obvious in areas of high contrast.

Bizarre....

thanks for your input
David Thiel wrote on 6/25/2008, 9:46 AM
John,
Thanks, I will check it out.
I am reticent to add another step to an already time consuming process but if the resulting DVDs look better I might do it.

I have a feeling that something is wrong with the MPEG2 compression codec/and or settings that DVDArch is using to recompress, but so far I haven't found them in the interface (other than to limit the lowest bitrate).

Thanks for your input.

david
MPM wrote on 6/26/2008, 8:53 AM
What about your graphics card - turn off any/all video acceleration if it has it. DVDA can use the GPU in Vista at least - I just checked.

FWIW I think your problem's in the processing (not necessarily the encoding), & to find a solution you might need to get over to the forums at videohelp.com where they have some folks *really* knowledgeable about the actual signal you're receiving itself and the Replay recording. My guess would be that might give you more of a target of what to look for on the system causing you problems.

Otherwise, a more trial/error approach:.. If it works on another PC, than obviously something's different on this one - step 1, do the exact same thing on both to make absolutely sure... often we forget one tiny step that proves critical.

Step 2, check the results and particularly what files are used on each machine *every* step of the way. Is it the same OS & SP? Do you have the same DS filters on each PC, are they the same versions, are the same filters &/or files used during each step? For example, Vista has several different video rendering processes from XP - in some cases You Just Can't do something in Vista that works flawlessly in XP.

"I have a feeling that something is wrong with the MPEG2 compression codec/and or settings that DVDArch is using to recompress..."

If it helps, David, my guess would be that the encoding itself is fine, but the problem is in translating the original picture into the source DVDA then uses -- IOW DVDA's encoder just compresses a snapshot of a displayed frame of video, and for whatever reason that snapshot's off. Maybe DVDA is doing something like stretching the image, or maybe it's not drawing the original properly to create the snapshot? In that case the encoding could be a faithful reproduction of what DVDA "see's" internally, & that's what you have to fix. Unfortunately that doesn't mean the cure is in DVDA.

You could feed DVDA a short test clip of mpg2 at the same bit rate & size that was rendered out of Vegas for instance & see what you get. If it does the same thing, something's preventing DVDA from doing it's job. If it's OK, then maybe something's off about decoding the Replay mpg? If the Replay mpg is the problem, maybe demuxing the file to get an m2v, then running it thru restream will give you some hints?
David Thiel wrote on 6/26/2008, 11:00 AM
GPU, that's interesting, I'll try that.

I have prepared the same file on both my old machine and new machine. No problem with the old machine and the artifact with the new machine. DVDArch can use a Replay MPG file and produce good results.

In parallel I have been dealing with someone from Sony support who insisted that the amount of compression was responsible. So I tried an experiment. I manually set the compression down from 8 to 7.9. The result had the same artifacts. If I don't recompress it looks fine.

Both machines are running XP with the same SP.

As far as DVDA exposes settings the file coming in has the same properties as the file going out, DVD MPEG settings so there shouldn't be any transformations and I haven't explicitly invoked any filters.

In any case MPM, thanks for your thoughtful suggestions.
MPM wrote on 6/26/2008, 12:28 PM
really, Really FWIW, David, I've been compressing video since the old Cinepak codec in ~92 - 93, & the picture you posted doesn't look like any sort of compression artifacts I've ever seen. The way compression happens, grossly oversimplified, is a frame is overlaid with a grid, and every rectangle in that grid gets analyzed to see what changes. If the changes exceed a threshold, they're recorded - if not, they're either left alone, or most often with higher compression, simplified further... That simplification amounts to freezing the picture or throwing out so much data that blocks of near solid color are visible. OR, it can appear that the video's being played behind a dirty, overlaid lens or screen. What I see in your snapshot is missing information like an improperly executed stretch of some sort - interlacing would be horizontal lines, compression would be rectangular across both dimensions, aliasing (jaggies) would be on diagonal lines (like zooming in to the pixel level), but frankly nothing I've seen was ever like this... to me it looks like something tried to stretch the data sideways but didn't interpolate the values needed to fill in all areas with missing information (to enlarge an image software had to literally guess at what goes in between existing pixels of color).

Now sat TV sends a shrunken image from the start AFAIK, that when captured direct (bypassing the box) is only 500 some pixels wide. Playback works similar to SVCD where the frame is resized horizontally from 480 to 720, or on an anamorphic wide screen DVD, where 720 width is expanded. Something in that original signal as captured by the Replay may be very slightly off, and what you see is a problem decoding the original that's magnified because of that file structure. Or it could be somehow frequency related - I really have no idea, but then I'm a total neophyte compared to some of the folks in the Videohelp forums.

It would be interesting to see how another program compresses the same video, or a sample of the same video anyway & compare it with DVDA. Video help.com has a few freeware encoding apps, or else you could use a trial of whatever. MediaInfo & Restream can each give you some valuable insight about the files themselves. If it helps, depending on the quality of your source you should be able to decrease bit rate to somewhere around 5 and still have an image that doesn't look too bad, Sony likes to use 8, & the max for most DVD software is at 9 - the lower the bit rate the more compression applied.