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Mark Curry
720p60 Playback Issue
on Feb 2, 2008 at 5:54:35 am

Hello,
I'm editing a 720p60 piece that consists of a continuous, very smooth motion dolly (on tracks) pan. However, on QuickTime playback the video exhibits occasional stutters. These stutters are not consistent temporally (i.e. stutters aren't always in same place). These stutters appear similar to dropped frames (i.e. the video jumps ahead a small amount). However, the system is keeping up as tested by FCP's dropped frames detection, and QuickTime's Playing FPS Info window reports a consistent frame rate.

On playback from tape to an HDTV there are no stutters. Also, tape printed from FCP (this footage which is sttutery in FCP and QT) also exhibits smooth playback on the HDTV. Clearly, this is some software playback issue.

Thinking that the complex MPEG-2 data was being misinterpreted by QT, I downconverted to Apple Intermediate Codec, ProRes 4:2:2 and various low data rate SD files always with the same sttutery result. This work is intended for QuickTime SD (.h264) downconverted playback (as well as HD ProRes 4:2:2 archiving) so I cannot avoid the issue. I'm next going to try a hardware (camera) SD downconvert, but this will introduce DV compression. Otherwise, I am approaching being stumped. Help ...

Specs:
HDV 720p60
JVC GY-HD200U camera
QT 7.3.1 (and also tried QT 7.4)
Leopard 10.5.1
FCP 6.0.2
Easy Setup 720p60
iMac 2.4GHz Duo

Mark





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johnny clark
Re: 720p60 Playback Issue
on Feb 3, 2008 at 3:35:01 am

Hello Mark,
It's hard to say but it sounds like a computer issue.
When I try to play footage (720p60 HDV) on my powerbook i get all kinds of studders and jumps but not on my Tower. Just make sure your Hard Drives and Memory are up to snuff. I'll look around for likewise issues.

Johnny C


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Mark Curry
Re: 720p60 Playback Issue
on Feb 3, 2008 at 6:05:42 pm

Yes, it does seem to be a performance playback issue except for the fact that the issue persists through transcoding to low-data rate Quicktimes (dv stream, photo-jpeg, h264).

However, my next step is test on a better rig: Mac Pro, internal SATA RAID, 2nd 23" monitor in order to eliminate this playback performance troubleshooting candidate.

Also, I'm going to try doing a hardware downconvert via the camera. As round-tripping to HDV via the camera is fine, perhaps downconversion via the camera will also be fine.




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Dave Sullivan
Re: 720p60 Playback Issue
on Feb 20, 2008 at 9:58:54 am

Umm, it does indeed seem like a system performance issue. Most playback problems, but not all I might add are caused by slow media/system drives, and or slow systems.
My system is quite powerful, but from time to time my system goes on strike, causing playback to be stuttery or just downright eratic!!
I'm not aware of any 720p 60fps encoding problems, but I will look into it.

All the best

Dave




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Justin Ferar
Re: 720p60 Playback Issue
on Feb 12, 2008 at 9:01:25 pm

I'm assuming you are not using a monitor with an Black Magic or AJA device- just using the computer monitor.

I know exactly what you are talking about. That little bump. I'm 99% sure it's a graphics card display issue. When I use my Black Magic Intensity I never see. When I use the graphics card hooked up to another LCD via DVI-D I see the bump.

Just to clarify, it's not actually in the footage, just a display issue. These are the little things you run into without a standardized pro rig such as BM or AJA. That said I think it's a damn good solution without having to pay $4-$10K.



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Mark Curry
Re: 720p60 Playback Issue
on Feb 14, 2008 at 6:19:30 pm

Hi Justin,

Yes, you're asssumption is correct - direct computer monitor and yes, the file is fine; it is playback that the issue.

I am excited to hear about you're experience with this bump (accurate characterization) as I can't find anyone else with this issue. Would you be able to take a look at the footage if I provide a link?

I do think it is weird however that all transcodes (including low data rate NTSC 29.97 PhotoJPEG, DV stream, etc) and the SD downconvert via the camera's analog outputs all exhibit this bump. Also, how is one supposed to distribute this? I can't expect all playback to be dependent on an Aja or Blackmagic device. I need to be able to output this thing in a way that can be distributed.

Next, I'm booked with post houses that have Kona gear and I'll also try capture to ProRes via firewire from the camera.




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Justin Ferar
Re: 720p60 Playback Issue
on Feb 14, 2008 at 6:40:43 pm

It's all system independent so there's nothing you can do to control that. All my compressed files for web act differently depending on the browser used (if viewing via web). If I have someone view a file from their desktop, which I think is what you are doing, I get stutters and bumps as well- and I have a Octocore Mac with 8 gigs of RAM! The only way for me to avoid all these things is to play the file back from my RAID but, because it's using quicktime and the graphics card for playback, I still get the bumps. The only way to avoid this 100% is hardware playback.

Hope this helps!



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Mark Curry
Re: 720p60 Playback Issue
on Feb 14, 2008 at 7:11:34 pm

This doesn't make sense to me. I know that browsers, players, etc interpret video differently (i.e. you cannot control these factors), but this is something else.

A low data rate, simple, spatially compressed QuickTime file should play back any current, out-of-the-box or well-maintaned Mac fine (with the usual caveats: no other applications running, standard QuickTime codec, etc.). In other words, if I have a SD 75% Photo-JPEG QuickTime playing back in 'kiosk' mode (i.e. no other apps running, networking disabled, Energy Saver set to max performance, etc.) on a current Mac (with RAM upgraded) the playback should be without stutters. I've certainly run this scenario many times in public exhibition for months on end. This is not heavy lifting for existing Mac graphics cards.



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