HDV Fast Action Distortion in Vegas

Mauriceh9 wrote on 2/4/2008, 9:25 AM

I am using a Sony HDV cam with Vegas 8.0b and have sucessfully captured some fast action areoplane display clips which in the extreme fill 50% of the frame. The clips look fine when played from the Trimmer, but after being moved onto the Timeline they exhibit distortionion. I.E. the group of planes flying in formation are overlayed by a shadow(s) like image offset from the main image and faded. I was actually filming with the planes coming towards me and as they passed overhead the speed of movement of the planes relative to the frame was increased as my camera panning was constrained by how far I was able to bend over backwards without falling on my butt. At this final point the movement of the planes relative to the frames was fairly high as they went out of shot. It is around this point in the clip that the distortion starts and is at its worse as as the planes go out of shot, with each frame showing the original image overlayed by 2 shadow images of the planes. Interestingly the background clouds do not appear to exhibit the same shadow distortion.

This isn't just a problem with the preview quality, because the distortion is carried through to the final rendered video.

My project settings are HDV 1080-50i (1440x1080, 25.000 fps) to match the HDV clips I've captured. It's strange that the images showing up in the preview window are different depending on whether being sent from the Trimmer or the Timeline. It's as if there is some sort of format conversion taking place when clips are put on the Timeline.

Be interested to know if anyone else has experienced a similar problem, or knows a setting that I'm not aware of that would cure the distortion.

Comments

DJPadre wrote on 2/4/2008, 1:19 PM

never ahd this issue with the fast moving stuff i do.. admitadly weddings, fashion and monster trucks arent as fast as jet planes, but i believe (and always have beleived) that what is in the vegas preview is NOT the actual format of the footage within the timeline. I always believed and am yet to have confirmation, that the prew window itself is a DV intra frame codec, be it sony or standard DV, as I HAVE noticed certain things "not quite right" on the vegas preview window.
I DO know its not a normal video overlay, as you can in fact capture the vegas timeline while itsel playing while, but try to capture this same file as screen dump (ie entire PC screen) while the video plays back in WM or VLC and the screen is black.

Another thing to consider is whether or not youre using filters on the clip in the timeline, and what yo umay be seeing is the recreation of the GOP structure which has flaked out due to the fast motion.

Have yo utried converitng the file to cineform and seeing the results ?

Shergar wrote on 2/4/2008, 1:49 PM

Are you sure this is not an interlace issue, or maybe even just excessive motion blur? Check your project settings. Try switching to/from progressive and check if the different deinterlace options give a better result.

farss wrote on 2/4/2008, 2:11 PM

I think you've nailed it. The trimmer preview only shows one field. Depending on the quality setting the T/L Preview will show 1 or both fields. Playing back the rendered output will be the same if rendering to HDV. If downscaling then make certain you have a de-interlace method defined in the project properties.

Bob.

rmack350 wrote on 2/4/2008, 2:47 PM

Vegas Preview window is definitely not DV. Pop some generated media on there and take a look. Or compare generated bars with bars rendered to DV.

I've always thought it was a plain uncompressed frame. Can you give me an example to look at that illustrates what you're seeing.

Rob Mack

Mauriceh9 wrote on 2/5/2008, 4:44 AM

Thanks for replies.

farss-
If the Timmer preview is only showing one field then it would suggest that the Timeline preview is showing what I've actually captured from the HDV cam to the m2t file i.e. both fields. This would suggest that that the capture process is at fault and one of the fields is being corrupted. I've re-looked at the original footage on my TV in composite mode and even played in slow motion it looks fine. I guess if there were a problem with the cam keeping up with the fast action then it would show up on the TV.

This could mean that I'm having a problem with the Vegas capture program. If that is the case I guess it could be lack of PC power, although given that I'm using a twin core 2.2 GHz fast hard drive laptop this ought not to be the case. Vegas recommends a 2.8GHz processor for HDV, but doesn't say anything about dual core requirements. Perhaps the capture process can't make use of the dual cores!

I think I need to confirm beyond doubt exactly what I've got in the original captured file. Can anyone recommend a way of playing back an m2t file outside of Vegas with both fields showing up, because the only other method I have is Windows Media Player, and that wont do it?

Shergar-
As this film is destined for DVD it is not going to be de-interlaced, so I'm not sure quite how changing the de-interlacing method in the project settings is going to help. Anyway I've tried it with no change to the result.

DJPadre-
I don't have anyway to convert to Cineform format, is there a free codec I could acquire to use within Vegas?

Thanks in advance for any help

Maurice

DJPadre wrote on 2/5/2008, 6:20 AM

cineform comes with vegas

jsut render to avi intermediate and use one of the presets.
Theyre set to "good" but i change mine to best

farss wrote on 2/5/2008, 6:32 AM

1) When you play the tape out to your TV you are sending 60i video to a 60i display device. The two fields that makeup a frame are displayed in the correct temporal sequence i.e. 60 fields per second.

When you look at the exact same footage from the trimmer you only see one field. When you view the footage from the T/L you see both fields merged into the one frame, there is no temporal separation. So if between field 1 and field 2 the plane moved half the frame size then you will indeed see two copies of the plane, half a frame apart.

If you look at the bottom of the preview window you'll a whole lot of information, take note of that as it tells you what is going on. If you change preview quality you'll see the info at the bottom of the preview window change from 30p to 30i. Try changing it to Preview Auto. I bet your 'ghost' plane vanishes and you'll see the info change to 30i.

2) As you're downscaling HD to SD and it's interlaced specifying a de-interlace method makes a HUGE difference in the quality of the downconvert. In interlaced video half the resolution is in each field. With no de-interlace method specified Vegas makes a mash of things leading to serious zagged edges on fast moving objects (like planes). As you're dealing with fast moving object you should set the de-interlace method to Interpolate. For slow moving I use Blend. When downconverting you really also need to use Best to force Vegas to use bicubic interpolation as well.

Before you worry about Cineform codecs and other complication try the above :)
Oh and if you're in PAL land then replace 30 with 25 and 60 with 50 in my explaination.

Bob.

Mauriceh9 wrote on 2/5/2008, 6:47 AM

Since my reply post earlier on today I got hold of a free copy of the VideoLAN player to play m2t files and was able to confirm that the problem is with the capture of my fast action clips. Not sure whether this is because of the fact that my PC is only 2.2GHz dual core rather than the minimum recommended spec of 2.8GHz single core. Seems a bit strange because you'd have thought it would either work OK or drop a frame. Anybody know whether there's anything I can do in the capture program to get over this problem?

I do have the option to capture at standard definition, which would presumably work OK. Might give it a try.

DJPadre-
Thanks for the steer on Cineform.

Maurice

farss wrote on 2/5/2008, 1:25 PM

How did you decide that???

Capturing works or not regardless of how fast the action is. It's a digital transfer, it has no idea of the content.

NickHope wrote on 2/5/2008, 8:22 PM

Doesn't sound like a capture problem to me either but you could try the excellent HDVSplit and see what happens. I had a couple of crashes in the past with it's preview turned on so you might want to turn that off to start with.

Mauriceh9 wrote on 2/6/2008, 9:17 AM

farss-

<<How did you decide that???

<<Capturing works or not regardless of how fast the action is. It's a digital transfer, it has no idea of the content.

Possibly a lack of knowledge on my part re HDV. I know that SD is simply a file transfer, so it matters not what's in the frame. However, I thought that HDV required some sort of conversion to m2t as part of the capture process. Also that an HDV file is not simply a a sequence of individually compressed frames, but rather something akin to mpg2 with GOP type structure. I therefore reasoned that there maybe more work to do in the conversion if there is a lot of movement from one frame to the next. But, with perhaps my limited understanding I've got it wrong. Always keen to learn new things.

Anyway I tried recapturing the problem clip in SD and got exactly the same result as with HDV. So whether my reasoning was right or wrong re the HDV capture hardware demand, the problem appeared not to be about capture. So having read your previous post re interlacing I began to wonder whether that was indeed the root of the problem somehow. I tried your suggestions with no improvement. I then began to wonder whether it was simply a case of the system not dealing very well with the display of interlaced video on an LCD screen, which only became apparent with extremes in speed of movement . As part of my search for an answer I had read that LCD was not a good match for interlaced video, and of course I've witnessed that in TV stores. So I created a DVD and played it through my CRT TV, and low and behold the problem was not in evidence.

My old desktop system setup used to include a TV so when previewing I could always see what the finished article would look like. However, having moved to a laptop I no longer have the TV access wired in. This exercise has made me realise that I have taken a bit of a step backwards in functionality.

Thanks to one and all for your help in solving the problem.

Maurice