24pa frame stutters - q from an editor

S

shill66

Member
Hello,
I'm editing a movie that I didn't shoot (hence I had no quality control over camera settings), and am entering confusing and unknown territory... any advice would be appreciated. Here's my situation:

The movie was shot on a Panasonic AGDVX100 in 24pa. All the footage was imported (by me) into Premiere Pro 1.5 as 24pa (project settings). I've completed the picture cut, and have rendered to AVI, which was brought into Encore to create a DVD.

When I play back the DVD, SOME of the scenes are jerky/stuttering, while the rest is smooth and fine.

Now, one thing I've already learned for next time is to output to elementary streams rather than an AVI, to bring into Encore. Okay, no problem, lesson learned. Haven't tried that yet.

My obvious question is how can I troubleshoot this problem? I can't know for sure that the camera settings were correct at ALL times during the shoot. If some footage was accidentally shot at 24p or 29.97 instead of 24pa, would I get this sort of result, remembering all was imported as 24pa? Or am I overlooking something else that I should already know but don't?

(I have a separate question about strobing on bright areas, and how do I eliminate it. But although that's a much smaller concern, it might be related.)
 
Instead of having Encore do the transcoding, use Premier to export it as a .m2v specifically for a 24 frame work flow (reset the GOP as required). This should make a big difference in the jerky/stuttering areas (unless the camera movement is too fast for the frame rate). Also gives you the advantage of being able to better optimize the bit budget.
 
on the strobing topic, one of the "problems" of premiere pro is that when working with 24p footage it adds that strobing effect to footage that is over exposed or rather NTSC unsafe (under 100IRE or digital equivalent 235 i believe) It has an easy fix and it will also ensure that your footage will be NTSC safe and wont bleed on certain television. Simply apply the levels filter or the color cerrection filter thats it you dont have to adjust any settings. for some reason those filters automatically puts it in safe margins and you will just have to render it out and the strobing goes away.
 
Thanks for the advice so far. I've just started my 9 hour render to .m2v and will see how it improves the situation. Later I'll apply the levels filter to fix the overexposed area strobing (at the moment I need a rough cut ready for tomorrow).

I've also realized that certain scenes were brought into After Effects and MAY not have been rendered the right way for 24p. I know how to do it, so I'll just re-render those and see if I'm right. But I still don't know if this is going to fix all my problems...
 
Well I'm not sure exactly HOW the clips got into "stutter" mode, but I know WHY they stutter, and I'm fixing them by re-importing the video, unlinking the old file and linking the new.

The rough cut screening (producers only) went well. Afterwards, our run time was cut from 1h44m to 1h40m, and we hope to trim it a bit more still.

Now I have an audio question to ask elsewhere...

http://www.unknown-movie.com
 
I have the exact same problems with my 24PA footage in Premiere Pr 1.5/Encore. I shot it, so I KNOW it's all 24PA footage. Some scenes all of a sudden, now stutter when burned to DVD or viewed in Windows Media Player. It looks FINE in Premiere. But when you're DVD stutters, you CAN'T blame it on just the Windows Media Player anymore! Those same scenes DIDN'T stutter in earlier cut versions.
 
NBCshooter said:
I have the exact same problems with my 24PA footage in Premiere Pr 1.5/Encore. I shot it, so I KNOW it's all 24PA footage. Some scenes all of a sudden, now stutter when burned to DVD or viewed in Windows Media Player. It looks FINE in Premiere. But when you're DVD stutters, you CAN'T blame it on just the Windows Media Player anymore! Those same scenes DIDN'T stutter in earlier cut versions.
Click to expand...

If the DVD stutters, then it is more than just a Media player issue. There are two methods used by progressive scan playback equipment (DVD players) to handle the task of deinterlacing any source. One involves cadence detection the other relies upon the flags within the GOP.

The first method (cadence) is often the better approach but requires a bit more processing (and added latency) from the deinterlacer. If the original source is a progressive one (film, progressive video) then it is a matter of using motion detection to identify the fields that made up the original frame. Then the process of creating the intermediate frames (those that are created based upon a frame or group of frames that occurred before and after) can be accomplished with less of a computational burden as the interframe motion is minimized. If the original source material is interlaced (60i) then each filed is rescanned (the old expression of line doubled) to make one progressive (60p) frame using a technique of interpolation.

If the deinterlacer within the playback device uses the GOP flag approach exclusively and if the GOP flags are corrupt (which can occur if the encoding software fails to properly set them) then you can end up with some rather exaggerated stuttering (likely worse than if it was interlaced footage to begin with).

What "could" be occurring is a pair of problems. The first is that the encoder used to create the MPEG stream failed to set the flags (repeat frame) properly and the wrong fields are being used to assemble the frame. Secondly, the DVD player is relying upon the flags and not the cadence detection scheme.

I would love to see a short clip of the problem to see if I can identify where the problem occurred. Likely, I would need to compare the original footage to the output from the MPEG encoder to be certain.

There is an answer to this, but it may be more than a single dimension issue.
 
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