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DVD 16x9 strobing issue on moving shots

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Chris Blair
DVD 16x9 strobing issue on moving shots
on Mar 16, 2009 at 6:37:30 pm

I posted this in the compression forum too.

We do a lot of compression and a fair amount of DVD encoding and authoring. We've encountered an annoying issue on our last couple of 16x9 projects that we've never seen before.

The DVD authored projects exhibit weird alaiasing on wide panoramic shots during diagonal moves (especially shots with lots of detail). This only occurs when played from a hardware DVD player and ONLY occurs on the extreme wide shots with diagonal movement. The moves are very slow and adhere to motion picture film panning rules for focal length, panning speed etc.

The aliasing isn't visible on camera moves on medium shots or closeups, or at least it's not objectionable. This only affects about 5 or 6 shots (our of hundreds) in either video.

Both projects used a variety of footage, from HD material shot on an HVX-200, to SD material shot on an SDX-900. All was shot widescreen and in 24P mode, then captured via SDI at 720x486 and edited 16x9. The videos look great playing back from the timeline on any monitor (even crappy ones) via component, SDI, S-video, composite, etc., and look great once output via SDI to DVCPro50 tape.

The ONLY difference in our workflow is we previously used Sonic ReelDVD software for DVD authoring, and now we're using Sony DVD Architect. I cannot imagine this would make a difference as we never recompress the video once it's exported from out NLE system (VelocityQ). MPG2 exports are done with years old presets and we know the files are compliant, not to mention we've done scores of projects using these in the past without seeing this issue.

There have also been no software updates to the non-linear software since this cropped up.

The videos look fine when played on a software DVD player on a computer, even if it's scaled to fill the frame at high resolutions on an LCD monitor. So I have to think there's something going on with the 3:2 pulldown or with progressive scan to cause the issue on a hardware DVD player.

Could the 16x9 flag that instructs a DVD to letterbox for playback on a 4:3 TV be the culprit?? The aliasing isn't as bad when played on a 16x9 TV, but it's certainly there.

Thanks





Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


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Jon Geddes
Re: DVD 16x9 strobing issue on moving shots
on Mar 17, 2009 at 1:17:57 am

You didn't explicitly mention this so I am going to ask...

Did you encode the file as 24p?

It sounds like interlace issues. Either it wasn't encoded into a 24p mpeg2 file, or somehow the fields are reversed (but this wouldn't affect a properly encoded progressive mpeg file).

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Chris Blair
Re: DVD 16x9 strobing issue on moving shots
on Mar 17, 2009 at 4:55:53 am

Jon Geddes
Did you encode the file as 24p?

It sounds like interlace issues. Either it wasn't encoded into a 24p mpeg2 file, or somehow the fields are reversed (but this wouldn't affect a properly encoded progressive mpeg file).


I've already tried encoding as a progressive MPG2 and saw only a slight improvement (if any at all). I've got to think it's the 16x9 flag that instructs a DVD player to letterbox the video for a 4:3 TV. This process has to resize the video vertically to fit it in the 4:3 frame with the correct aspect ratio. The aliasing is definitely worse on 4:3 TVs. To test, I encoded the video without the 16x9 flag, burned to DVD and played on a 4:3 TV. The problem shots looked fine (of course the video was stretched vertically since it filled the 4:3 frame). So that must be the issue here.

I also played the 16x9 DVD on multiple player/TV combos and the strobing varies in intensity depending on the brand and age of the DVD player. The one we test on is old as dirt as is the TV it's hooked to. We do that on purpose because if this 10 year old player and TV will play the DVDs, ANYTHING will.

But even a 1 year old Panasonic DVD player hooked to a new Sony Luma series LCD showed a little of the aliasing, just not as bad.

The Panasonic cameras add their own 3:2 pulldown during the recording process and our NLE systems don't offer pulldown removal or anything like that upon capture, so all projects are edited as 29.97 timelines with the pulldown left intact. So when we encode, we just export normally (rather than 24P).

There's never been an issue unitl these last two projects. This is a period that covers literally hundreds of projects using thousands of shots of all varieties.

It's not a field order issue as more than just the few shots mentioned would exhibit aliasing and strobing. So I think that only leaves the letterboxing flag that fits the video to the 4:3 frame. I'll probably encode using Carbon Coder for the final output, which has a ton more options. That should significantly reduce the problem.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


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Jon Geddes
Re: DVD 16x9 strobing issue on moving shots
on Mar 17, 2009 at 6:16:47 pm

I would be interested in hearing the results of a proper 24p workflow, with no pulldown in the editing process. You should be editing in progressive mode, because in your current workflow, if you need to render something, it will do it interlaced with no pulldown applied unlike what the raw footage is.

I would take those shots into a program that can remove the pulldown, in a true 24p project, transcode them into a 24p mpeg, burn and test.

We shoot everything in HD, so naturally its all widescreen, and I've never seen the issues you are describing. Its very possible that the problem exists in the rest of the video, but its just not noticeable because of the amount of motion or it just blends in (low contrast). Did you happen to do any effects on the wide shot that it had to render?

I'm willing to bet its a problem somewhere with your workflow and not from the 16:9 flag. Either your fields are reversed on the mpeg file, or its from the lack of pulldown removal during the editing process.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Chris Blair
Re: DVD 16x9 strobing issue on moving shots
on Mar 17, 2009 at 10:33:43 pm

I'm not trying to be contentious here....I sincerely appreciate you taking the time to answer my post and give suggestions so don't take this post the wrong way!!!

We edit exclusively with the VelocityQ systems (3 of them) so we don't have any way to test the 24P workflow theory.

But we had long discussions about the whole 24P/29.97 edit workflow question via the http://www.cinematography.com forum with the Panasonic varicam rep, as well as face to face with our regional rep before we bought this camera and they consistently said there are a ton of myths floating around about that issue.

Editing with their 24P footage (with pulldown) on a 29.97 timeline is no different than editing with 16mm or 35mm film telecined to video, (which we also used to do a lot of). That came directly from 2 Panasonic folks, one of whom is generally considered an expert about their varicam cameras.

Rendering or exporting doesn't affect the fields or pulldown (as long as field order is correct, which it is). It should encode to the MPG2 file as a 29.97 file with the pulldown intact. Modern DVD's should recognize the pulldown and handle playback fine. Again...this isn't me saying this stuff...this is Panasonic folks.

When we export, we have the option of exporting with interlaced fields or with progressive frames, and we use interlaced (again...straight from Panasonic recommendations using 24P with pulldown). If it were a field order issue, motion graphics would stutter, still graphics would look fuzzy and out of whack, and all the video would generally look bad.

Just last week we ouput a 4x3 video for this same client (a revision of a 3 year old video) that was shot with the SDX-900 at 24P; edited with the exact same workflow, with very similar type shots, then output to DVD using the same presets and DVD authoring app.

We see none of the strobing/aliasing. In fact, some of the shots are from the exact same location (framing, angle etc.) and use the same camera moves. So the whole 24P workflow problem doesn't hold water there.

Not to mention that exporting the offending project to MPG2 and authoring as a DVD without the 16x9 flag eliminates the strobing. That tells me there's something going on either in the encode (it's a fairly old Ligos encoder in the VelocityQ editing systems), or in the letterboxing instructions when it's played to a 4x3 TV.

It also doesn't explain why we've never seen this issue across hundreds of projects going out to DVD over the last 5 years using the exact same 24P workflow, many 16x9.

As I said in a previous post, we're going to export using Carbon Coder and see what we get. I bet that fixes the issue.




Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


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Jon Geddes
Re: DVD 16x9 strobing issue on moving shots
on Mar 18, 2009 at 4:42:01 am

What I was implying is that, in general, a 16:9 flag does not cause the problem you are describing, otherwise all hollywood movies would have serious issues. I wouldn't be surprised if it had something to do with the encoder. What I seriously doubt is that the problem is simply from the 16:9 flag. It is however possible that the encoder has problematic algorithms when encoding 16:9 footage... again, this would be an encoder problem, and not simply a problem inherent of all dvd's encoded with a 16:9 flag.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Chris Blair
Re: DVD 16x9 strobing issue on moving shots
on Mar 18, 2009 at 12:27:39 pm

Yup...I think that's likely it. We exported a section of the video, brought it into Premiere CS3, then exported from there for DVD and it looked fine from the DVD. Also brought it into Vegas and did the same thing.

We rarely use either of those editing apps for actual projects, but that confirms it's not the footage or workflow.

Thanks for the help

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


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