High Action/Motion Video from HVR-V1U

[Alex Raskin]

Piotr, it does look the same as on HDTV, just like I pointed out :)

Any fast motion in the frame (or busy background) = blocky artifacts.

Since this only occurs during motion, the motion blur itself does mask the artifacts somewhat.

However I can see them during normal playback, and they are extremely obvious on frame-by-frame viewing in NLE.

Sony Z1 and V1 both seem to produce similar artifacts.

(On cable HD TV, similar blocky artifacts even occur during fades between the scenes. Urgh.)

This is all because of low-bandwidth mpeg-2 compression.

Supposedly, higher bandwidth (50Mb/s) devices like XDCAM HD or EX, do not exhibit such problems.

In fact, V1U also does not have any macroblocks on fast motion if you capture *live* via HDMI, since it outputs uncompressed 1920x1080 signal.

Live HDMI signal is before mpeg2 compression.

Now all we need is a laptop with Blackmagic Intensity card built-in, for mobile video capture on location
:)

[Steve Mullen]

Originally Posted by Alex Raskin

(On cable HD TV, similar blocky artifacts even occur during fades between the scenes. Urgh.)

Perhaps you have COMCAST or your cable company is getting a multicast. :)

I have a dozen HD channels on COX -- who does not rate limit and gets feeds direct from the stations -- and this simply in not the norm. But, it does occasionaly happen. I don't why.

So I'm not saying you don't see what you see, but it is not inherently true of 19.4Mbps MPEG-2.

[John Cash]

I will take the wakeboarding footage, send it through FCP and burn a disc then report back. Its true that I have been watching the footage on an HDTV ..however Im using the component inputs. So let me check what my footage looks like after rendering and burning. I do have some snowboard footage I have put out as a Quicktime movie on my PC...and NO background blur there

[Alex Raskin]

Steve, my HD broadcast provider is Cablevision in North East US. I saw exactly the same artifacts on my older DirecTV HD two years ago though, as well as over-the-air HD broadcast of FOX, ABC, and PBS, so I assumed all broadcasters are bottlenecking at the mpeg2 codec.

John, while in FCP, simply go frame-by-frame and you will see the artifacts.

You are *not* looking for the blur, but for the squares (blocks) that will appear on fast-moving parts of the image.

They look completely unnatural.

Not only do they occur on the moving parts, but sometimes also on the steady parts of the image, for a few frames following the fast motion, arbitrarily. Clearly the mpeg2 codec gets thrown off and cannot keep up with the action at 25Mbs and less.

I read some articles than JVC HD250 cam has what they call SuperEncoder that somehow encodes better, but I have no first-hand experience with that. (Note that HD250 only records 720p, while V1U outputs 1080p, making mpeg2 encoder work harder.)

I also believe that pro cams that record mpeg2 in 50Mbs streams have enough bandwidth to *not* exhibit motion artifacts - but then again, I have no personal experience working with that footage yet.

[Piotr Wozniacki]

I personally did never notice any macroblocking on my V1E (apart from what sometimes happens when a photographer's flash changes quickly the lighting conditions where I'm shooting).

The only evidence of the HDV encoder running out of bandwidth that I do encounter when shooting progressive is the dancings pixels, or marching ants occuring near sharp, contrasty edges with plenty of small detail. This has nothing to do with high action/motion, though.

[Alex Raskin]

OK, here: this was shot with V1U last week in Central Park NYC, recorded on tape (HDMI *not* used).

The setup: girl's head is between the camera and the guy.

Girl moves to the right and out of the frame, fast.

See the trail of macroblocks on her hair and to the left.

Guy's face in the background is also affected (and will be for a couple of frames even after the girl is completely out of the view.)

Tree on the left is far enough from the action and is unaffected.

I captured that frame from the NLE as bmp, and then saved as jpg to decrease file size. This did not change how the still cap looks.

So there you go.

[Piotr Wozniacki]

Yeah, this definitely is ugly. Does it last long enough to actually see it when playing at normal speed?

Again, I've never spotted anything like this on my recordings. When I find a single frame that looks as bad, I'll let you know!

[Alex Raskin]

You can hardly ever notice it at normal speed.

In my case, it lasted for a few frames altogether.

That's why people think the blockiness is not there.

FYI, this was shot at 24p, but it does not matter - the same thing occurs at 30p and 60i. Z1U did the same thing too.

Once again, V1U cam is actually great: simply capture from HDMI out live (i recommend Cineform Aspect HD as codec of choice), and voila - no macroblocks on fast motion.

I'm not affiliated with Cineform, just love their AHD codec.

[John Cash]

next week I will be installing the Blackmagic HDMI capture card. No more MPEG 2 capture for me, so I hope that will do away with this problem

[Brandon Freeman]

Weird. I've been shooting with the Z1U for a few years, now, and haven't seen these artifacts at all (and I scrub back and forth on single frames in Vegas all the time).

[Piotr Wozniacki]

Originally Posted by John Cash

next week I will be installing the Blackmagic HDMI capture card. No more MPEG 2 capture for me, so I hope that will do away with this problem

I guess you realize that only live HDMI capture will let you avoid HDV compression?

[John Cash]

So, if I record to tape and watch it on HDTV via HDMI cable its still compressed at Mpeg2? And the only way to capture via HDMI without compression would be to use a hard drive instead of tape?

[Piotr Wozniacki]

As I said, and Brandon confirmed - this is really weird. I do a lot of scrubbing of my HDV material in Vegas and have seen many things you can't notice when watching the normal speed video, but never came across such evident macroblocking.

[Piotr Wozniacki]

Originally Posted by John Cash

So, if I record to tape and watch it on HDTV via HDMI cable its still compressed at Mpeg2? And the only way to capture via HDMI without compression would be to use a hard drive instead of tape?

John, HDMI is uncompressed. But, if you first compress in order to write to tape (or disk drive such as HVR-DR60 or Firestore), you're certainly not going to get rid of the compression artefacts, should any occure during the original compression process. HDV, or more generally MPEG-2, is not a lossless codec and what is lost, cannot be recovered.

Therefore, to avoid compression artefacts, one needs to capture uncompressed (HDMI with Blackmagic is one option) before, or without ever writing to tape/hdd recording unit.

[Brandon Freeman]

Originally Posted by Piotr Wozniacki

As I said, and Brandon confirmed - this is really weird. I do a lot of scrubbing of my HDV material in Vegas and have seen many things you can't notice when watching the normal speed video, but never came across such evident macroblocking.

Correction -- I have seen macro blocking when shooting standard interlaced 60i or 50i, BUT when I shoot in CineFrame30 or CineFrame25*, the motion artifacts are gone. I had always figured that the interlacing added an extra burden for MPEG encoders, and thus don't do anything other than interviews in standard 60i.

*I understand that CF30 and CF25 are not true progressive, but it sure looks purty. :)