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Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.

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Cosmin Gurau
Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 3:10:13 am
Last Edited By Cosmin Gurau on Apr 6, 2014 at 3:11:30 am

I imported in Vegas Pro 12 a 480x360 mp4 file, and was shocked at the horrible quality (lots of degrading macroblocking) that I was seeing in the preview, remembering that it didn't look half as bad when I saw it in my media player. So I simply re-encoded the file in VirtualDub, into a lossless format, and replaced the file. It looked worlds apart better.


preview of the video file imported in Vegas


preview of the video file imported in Vegas after re-encode (of the same file) through VirtualDub

details.jpg
details of the file in MediaInfo


So I thought I change my preview quality to "Good(Full)" from "Preview(Full)" and the macroblocking magically disappeared. Sure, all is fine and dandy now, but I can't handle that high quality preview all the time when I edit...

I really doubt my PC has anything to do with this macroblocking issue, I have a pretty old, yet still half decent one, an Intel Core 2 Quad @ 3.4 Ghz, 8 GB RAM, GTX 680...

Is this normal behavior? Have you guys encountered this issue? Sony always DID handle the h.264 codec weirdly... what with the Computer RGB to Studio RGB fix and all. Any knowledge would be appreciated.


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Rick Anvican
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 11:31:40 am

Hi Cosmin,
The AVC video codec is a lossy inter-frame format designed for delivery purposes, meaning that it compresses video in that in a group of pictures (GOP), the 1st frame is a full image while frames that follow are predicted based on the 1st frame, therefore requiring calculation of differences to create those predicted frames.
Vegas tends to show artefacts like macroblocking and banding in Preview|Full when using AVC because of the lower accuracy needed to calculate frames. Importing the lossless version means that Vegas does not need to recreate prediction frames because the codec you're using is likely an intra-frame codec like Lagarith, which are suitable for editing purposes as they compress with each frame being full images, so this should lighten up the load for previewing in Good|Full.

Vegas could edit AVC video but it doesn't mean that it is the most compatible format, you're more likely to encounter problems with sources using interframe codecs(e.g. AVC, MPEG2) than intraframe codecs (e.g. DV-AVI, Lagarith), hope this helps,

RickAVC


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Bob Peterson
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 12:01:30 pm

You should not expect preview quality to produce a pristine image no matter what format the source file is in. Vegas is NOT TRYING to give you a pristine image in preview. That is the point of preview mode. Preview is meant to give you the best possible framerate while you are editing the file. If you are doing things that require you to see a high quality image, you should switch to best(full) which will show you the kind of image quality that a render is capable of producing if you render at a high quality.


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Cosmin Gurau
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 12:22:46 pm

Thanks for the explanation Rick, and Bob. But I still don't understand why more heavily encoded files, like the video files from my Nikon D7000 or any full HD AVC files for that matter do not have these kind of problems...

In fact, after a bit more testing, it seems the only cases I ever notice such severe macroblocking inducing behavior is with YouTube downloaded videos, which should in theory need less computing power to decode, right? Maybe I'm not understanding something...


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Rick Anvican
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 12:45:14 pm

Like what Bob said, the preview is a tradeoff between framerate and quality, in real-time previewing you can't have both with limited resources.
Vegas should be able to read AVC files from cameras fine, editing YouTube videos would not be ideal - they're more compressed than the files from your cameras and can make Vegas glitch. You're not using codec packs, right?


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John Rofrano
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 2:25:55 pm

[Cosmin Gurau] "But I still don't understand why more heavily encoded files, like the video files from my Nikon D7000 or any full HD AVC files for that matter do not have these kind of problems..."
Because in the case of Full HD, Vegas Pro is only decoding the video. In the case of your 480x360 mp4 file, Vegas is Scaling the video in addition to decoding. For Preview quality it is probably use the "nearest neighbor" algorithm to rescale which is very fast but causes blockiness. For Good/Best/Full quality it is probably using the "bi-cubic" algorithm which requires more compute power but yields higher quality results. So it's the algorithm being used to resize the video that it making you 480x360 mp4 file look different from your Full HD files because the Full HD files don't need to be resized.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Cosmin Gurau
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 7, 2014 at 6:08:09 am

Wow, Thanks, John. It makes sense now...

Um... Yes, I do, Rick, I do use the K-Lite Codec Pack (full options)... Why?


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Rick Anvican
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 7, 2014 at 6:29:35 am
Last Edited By Rick Anvican on Apr 7, 2014 at 10:59:33 pm

We don't expect everybody's computer or workstation that runs Vegas to have the same programs and codecs installed, although it's been found that Vegas 12 is a lot more stable when dealing with codec packs, they may cause problems for some systems, like being unable to import certain formats or a broken/glitchy preview, I'm not suggesting that you should uninstall it, but this thread has some findings by other members if you're interested: http://forums.creativecow.net/thread/24/963924


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John Rofrano
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 7, 2014 at 4:50:00 pm

[Rick Anvican] "I'm not suggesting that you should uninstall it, as long as Vegas works fine for you"
Considering that Vegas is NOT working fine for you and that you are complaining about heavy macro blocking, I would absolutely uninstall the K-Lite codec pack, uninstall Vegas Pro, reboot your computer, and reinstall Vegas Pro and see if it fixes the problem. K-Lite has been knows so seriously mess with Vegas Pro functioning properly.

While the resizing that I explained may have had something to do with it, I wouldn't be surprised if K-Lite added to the poor quality because it replaces the high quality codecs that you paid Sony for, with open source codecs of questionable quality. This could definitely be contributing to your problem.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Norman Black
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 6, 2014 at 4:51:42 pm

[Cosmin Gurau] " from my Nikon D7000 or any full HD AVC files for that matter do not have these kind of problems...

In fact, after a bit more testing, it seems the only cases I ever notice such severe macroblocking inducing behavior is with YouTube downloaded videos"


Youtube/Vimeo files are low bitrate. Your D7000 and other camera files are high bitrate. Video quality always comes down to bitrate.


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Dave Haynie
Re: Shockingly, Vegas introduces HEAVY macroblocking on "Preview (Full)" quality in the case of a small res mp4 file.
on Apr 7, 2014 at 7:28:48 pm

Yup... there's low bitrate and there's low bitrate. AVC from a camcorder or DSLR isn't all that low in bitrate. A typical AVCHD camcorder will deliver 1080/60i or 1080/24p at 24Mb/s, which is higher bitrate than the maximum ATSC broadcast rate of 19.4Mb/s... AND you're AVC. A good AVC encoder will have about twice the coding efficiency of the MPEG-2 used in ATSC. I'm not sure about the Nikon, but Canon DSLR video is usually at around 31Mb/s (newer IPB models) or 44Mb/s (older IP-only models), or 91Mb/s for I-Frame Only video on the more recent cameras.

Of course, blocking is also easier to see on a small video blown up to comfortable desktop viewing size than it is for a larger video. But the principle is the same. In pretty much all of the MPEG encoders, the video broken up into those blocks that you see, called macroblocks. Each of those gets its own discrete cosine transform, which is similar to a discrete Fourier transform, it's converting spatial information to frequency information... and that's reversible and lossless (well, aside from rounding errors). Then there's the lossy part, a decimation pass that tosses out a certain amount of the higher frequency information any macroblock. Then that whole thing is losslessly compressed using Huffman or similar entropy encoding... and the process is reversed on the expansion.

When you see the macroblocks, what you're seeing is essentially too much low-pass filtering... the content of one cell no longer quite matches the content of the next cell, and your brain, with it's advanced image processing wetware and particular fascination with horizontal and vertical lines, fills in that mismatch as a line that isn't really there. I'm sure lots of folks here understand this, but I figured I'm mention it.

So there are only two options to get rid of those macroblocks in most parts of the video. One is simply increasing your rendered bitrate. With a higher bitrate, there's less filtering at each macroblock, and less chance that ajacent macroblocks no longer line up. The other thing you can do is run a slight blur over the video prior to encoding. "Blur" is another name for "low pass filtering". When you remove high frequency information at a frame-global level, you're eliminating the uneven removal of that same information in each macrocell... so you can have the higher compression without macroblocks being visible.

There's one other case in MPEG you'll see way too much macroblocking, and that's in fast motion video. That's because of the P and B frame types. An I-Frame is basically just a fancy Motion JPEG image. P and B frames use various motion prediction algorithms to essentially describe themselves in terms of the preceding (and for B, the subsequent as well) I-Frame. So what's actually stored isn't a whole frame, but that tiny set of motion vectors, and the difference between the predicted frame and that actual one. Which ideally is practically nothing... because "nothing" compresses really well. But once you have too much motion, the whole thing kind of breaks down, and you're left with a tiny fraction of the I-Frame space to record a really big difference between last and predicted frames. So you see big artifacts then things get too fast... I have a Panasonic 3-chip consumer camcorder that's even polite enough to detect this and warn you about it (my other cameras assume I know what I'm doing, and of course, a DSLR in I-Frame-only mode don't care).

-Dave


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